Thick Disks of Lenticular Galaxies

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高三宇宙奥秘英语阅读理解30题

高三宇宙奥秘英语阅读理解30题1<背景文章>Black holes are one of the most fascinating and mysterious phenomena in the universe. A black hole is formed when a massive star collapses at the end of its life. The gravitational pull of a black hole is so strong that nothing, not even light, can escape from it.The formation of a black hole begins with the collapse of a massive star. As the star runs out of fuel, it can no longer support its own weight and begins to collapse. The collapse continues until the star reaches a critical density, at which point it becomes a black hole.Black holes have several unique characteristics. One of the most notable is their event horizon, which is the boundary beyond which nothing can escape. Another characteristic is their intense gravitational field, which can distort the space and time around them.Black holes can have a significant impact on the surrounding celestial bodies. They can attract and swallow nearby stars and planets, and their gravitational pull can also affect the orbits of other celestial bodies.Scientists are still working to understand black holes better. They use a variety of tools and techniques, such as telescopes and computer simulations, to study these mysterious objects. Despite significant progressin recent years, there is still much that we don't know about black holes.1. What is a black hole formed by?A. A small star collapsing.B. A massive star collapsing.C. A planet collapsing.D. A moon collapsing.答案：B。

The Extreme Outer Regions of Disk Galaxies I. Chemical Abundances of HII Regions

Unfortunately, most HII region abundance studies carried out to date have probed only the bright, easily-observed inner regions of galactic disks, lying at or within the classical optical radius, R25 (deﬁned by the B-band 25th magnitude isophote). It is well known, however, that disk galaxies have HI disks which extend to typically ∼> 1.5–2 R25 (eg. Cayette et al 1994; Broeils 1994), and in some rare cases to ∼> 3R25 (eg. van der Kruit & Shostak 1984). These outer regions are characterized by low HI columns, high gas fractions and long dynamical timescales and thus provide an opportunity to study star formation and chemical evolution in rather unique physical environments. Indeed, the outer regions of disks have physical properties which are reminiscent of those thought to exist during the early stages of galaxy formation, as well as those in giant low surface brightness galaxies, such as Malin 1 (eg. Pickering et al 1997). Studying the mean enrichment level, the shape of the abundance gradient and the amount of intrinsic scatter at ﬁxed radius, in outer galactic disks will therefore forward our understanding of a broad range of astrophysical objects. Furthermore, since the predictions of models of chemical evolution often diverge most strongly in the outer parts of galaxies, abundance determinations extending as far in the outer disk as possible are needed to discriminate between competing theories.

Oxygen in the Galactic thin and thick disks

a rXiv:as tr o-ph/21229v12Dec22CNO in the Universe ASP Conference Series,Vol.**VOLUME***,**YEAR OF PUBLICATION**C.Charbonnel,D.Schaerer &G.Meynet,eds.Oxygen in the Galactic thin and thick disks T.Bensby,S.Feltzing,and I.Lundstr¨o m Lund Observatory,Box 43,SE-22100Lund,Sweden Abstract.First results from a study into the abundance trends of oxy-gen in the Galactic thin and thick disks are presented.Oxygen abun-dances for 21thick disk and 42thin disk F and G dwarf stars based on very high resolution spectra (R ∼215000)and high signal-to-noise (S/N >400)of the faint forbidden oxygen line at 6300˚A have been de-termined.We ﬁnd that [O /Fe]for the thick disk stars show a turn-down,i.e.the “knee”,at [Fe/H]between −0.4and −0.3dex indicating the onset of SNe type Ia.The thin disk stars on the other hand show a shallow decrease going from [Fe /H]∼−0.7to the highest metallicities with no apparent “knee”present indicating a slower star formation history.1.Introduction The Galactic thin and thick disks are two distinct stellar populations in terms of age distributions and kinematics.The chemical trends in the two systems are also most likely diﬀerent although recent works give conﬂicting results,see e.g.Chen et al.(2000)and Fuhrmann (1998).We show that the abundance trends for oxygen are diﬀerent for the thin and thick disks.2.Observations The selection of thin and thick disk stars was based on kinematics and is fullydescribed in Bensby et al.(2003a,in prep).We calculated Gaussian probabil-ities for each star that it belongs to the thin and thick disk respectively,using the galactic velocity components U ,V ,and W of the stars.Stars with high probabilities of belonging to either the thin or the thick disk were then selected.The sample consists of 21thick disk stars and 42thin disk stars.Spectra were obtained with the CES spectrograph on the ESO 3.6m tele-scope with a a resolution of R ∼215000and a signal-to-noise S/N >400.Telluric lines were divided out using spectra from fast rotating B stars.Further details are given in Bensby et al.(2003b,in prep).3.Abundances and resultsOxygen abundances were determined through ﬁtting of synthetic spectra to the observed spectra.The forbidden oxygen line at 6300˚A that has a blend of nickel in its right wing.At low metallicities this blend is often negligible,but12Bensby et al.becomes severe at higher metallicities.This is illustrated in Fig.1where we plot synthetic and observed spectra for three stars at diﬀerent metallicities.Fe and Ni abundances have been determined from our FEROS spectra(R∼48000)by measuring equivalent widths of approximately140Fe i,30Fe ii,and50Ni i lines for each star(Bensby et al.2003a in prep.)Figure1.The forbidden oxygen line at6300˚A for three stars withdiﬀerent metallicities;HIP103458(thick disk),HIP96124(thick disk),and HIP78955(thin disk).The observed spectra are plotted with solidcircles.Three diﬀerent synthetic spectra are shown for each star:onlythe forbidden oxygen line(dashed line),only the blending nickel line(dotted line),combination of the two(solid line).The two plots in Fig.2presents our results.These are ourﬁndings:1.The thin and thick disk stars clearly show diﬀerent abundance trends.This is a strong indication of their disparate origin and diﬀerent epochs of formation.2.A turn-down for[O/Fe]at[Fe/H]∼−0.35for the thick disk stars,from being roughlyﬂat,continuing down to solar values.This feature is most likelya signature of the onset of SNIa.3.The thin disk stars show a shallow decrease when going from the lowest metallicities to solar values,not showing a knee.This implies that the star for-mation rate in the thin disk was quite low compared to that in the thick disk.4.At super-solar metallicities the trend found at sub-solar metallicities contin-ues linearly for the thin disk stars.In contrast Nissen and Edvardsson(1992) found[O/Fe]to level out at these metallicities.However,they did not take the Ni i blend in the[O i]line into account,which becomes important at these metal-licities,see Fig.1.This result has implications for diﬀerent models of supernova yields,and will be investigated further.Oxygen in the Galactic thin and thick disks3Figure2.Abundance trends for oxygen.Thick disk stars are markedbyﬁlled circles and thin disk stars by empty circles.All stars have also been observed with the FEROS spectrograph and abun-dances for other elements have been determined(Na,Mg,Al,Si,Ca,Sc,Ti, V,Cr,Mn,Fe,Co,Ni,Zn,Y,Ba,Eu).For theα-elements weﬁnd the same signature from the onset of SNIa in the thick disk which appears to be absent in the thin disk,see Feltzing et al.(2002)and Bensby et al.(2003a,in prep),in good agreement with the trends weﬁnd for oxygen.A few stars merits,due to their positions in Fig.2,further comments:two thick disk stars at[Fe/H]∼−0.3and one thin disk star at[Fe/H]∼−0.6.The latter may be due to the fact that the thick disk also contain stars with“cold”kinematics.Theﬁrst two are a bit harder to understand but their kinematics might have been heated through close encounters or they might have been kicked-out from a double or multiple stellar system.ReferencesBensby,T.,Feltzing,S.,&Lundst¨o m,I.2003a and2003b,both in preparation Chen,Y.Q.,Nissen,P.E.,Zhao,G.et al.2000,A&AS,141,491Feltzing,S.,Bensby,T.,&Lundst¨o m,I.2002,A&A,in press(astro-ph/0211589) Fuhrmann,K.1998,A&A,338,161Nissen,P.E.,&Edvardsson,B.1992,A&A,261,255。

宇航员英语试题及答案

宇航员英语试题及答案一、选择题（每题2分，共20分）1. What is the term for a person who travels in space?A) AstronautB) NavigatorC) PilotD) Engineer2. The International Space Station (ISS) orbits the Earth approximately how many times a day?A) 15B) 24C) 30D) 453. Which of the following is NOT a stage of a rocket launch?A) IgnitionB) Lift-offC) AscentD) Descent4. What does NASA stand for?A) National Aeronautics and Space AdministrationB) North American Space AssociationC) National Association for Space AdvancementD) None of the above5. Who was the first person to walk on the moon?A) Neil ArmstrongB) Buzz AldrinC) Yuri GagarinD) Alan Shepard二、填空题（每题1分，共10分）6. The first human-made object to reach the surface of the moon was ________.7. The term "zero gravity" is often used to describe thestate of ________ in space.8. An astronaut's job can be described as ________ and________.9. The sun is a ________ star, and it is the center of our solar system.10. The first woman to walk in space was ________.三、简答题（每题5分，共30分）11. Explain the purpose of a spacesuit.12. What is the significance of the Hubble Space Telescope?13. Describe the process of docking a spacecraft with the ISS.14. What are the challenges faced by astronauts during long-duration spaceflights?四、阅读理解（每题2分，共20分）Read the following passage and answer the questions.The Mars Rover is a robotic vehicle designed to explore the surface of Mars. It is equipped with various scientific instruments to gather data about the planet's geology, climate, and potential for past life. The first successful Mars Rover was Sojourner, which landed on Mars in 1997. Sincethen, several other rovers have been sent, each with more advanced capabilities.15. What is the primary function of the Mars Rover?A) To communicate with EarthB) To explore the surface of MarsC) To study Mars' atmosphereD) To transport astronauts16. When did the first Mars Rover land on Mars?A) 1997B) 2000C) 2005D) 201017. What kind of data does the Mars Rover collect?A) Only geological dataB) Only climatic dataC) Geological, climatic, and potential life dataD) Data on Mars' potential for future human colonization18. How many Mars Rovers have been sent to Mars since the first one?A) OneB) TwoC) ThreeD) Several19. What is the name of the first successful Mars Rover?A) CuriosityB) OpportunityC) SpiritD) Sojourner20. What does the passage imply about the capabilities of later Mars Rovers compared to the first one?A) They are the sameB) They are less advancedC) They are more advancedD) There is no information provided五、写作题（共20分）21. Write an essay about the future of space exploration and how it might benefit humanity. (200-250 words)答案：一、1. A2. A3. D4. A5. A二、6. Luna 27. weightlessness8. scientific research, exploration9. G-type main-sequence10. Svetlana Savitskaya三、11. A spacesuit is designed to protect astronauts from theharsh conditions of space, such as extreme temperatures, vacuum, and radiation. It provides life support, maintains pressure and oxygen levels, and allows for mobility during spacewalks.12. The Hubble Space Telescope has been instrumental in expanding our understanding of the universe. It has provided high-resolution images of distant galaxies, nebulae, and stars, contributing to significant discoveries in astrophysics.13. Docking a spacecraft with the ISS involves a carefully choreographed sequence of maneuvers, including approaching the station, aligning with it, and securing the connection using a docking mechanism.14. Long-duration spaceflight presents challenges such as bone density loss, muscle atrophy, psychological effects, and exposure to radiation.四、15. B16. A17. C18。

高一年级英语天文知识单选题40题

高一年级英语天文知识单选题40题1. Which planet is known as the "Red Planet" because of its reddish appearance?A. EarthB. MarsC. JupiterD. Venus答案：B。

解析：在太阳系中，火星（Mars）因为其表面呈现出红色的外观而被称为“Red Planet（红色星球）”。

地球（Earth）是我们居住的蓝色星球；木星（Jupiter）是一个巨大的气态行星，外观不是红色；金星 Venus）表面被浓厚的大气层覆盖，不是以红色外观著称。

2. Which planet has the most moons in the solar system?A. EarthB. MarsC. JupiterD. Mercury答案：C。

解析：木星（Jupiter）是太阳系中拥有最多卫星（moons）的行星。

地球（Earth）只有一颗卫星；火星（Mars）有两颗卫星；水星 Mercury）没有卫星。

3. The planet with the shortest orbit around the Sun is _.A. MercuryB. VenusC. EarthD. Mars答案：A。

解析：水星（Mercury）是距离太阳最近的行星，它的公转轨道是最短的。

金星 Venus）、地球 Earth）、火星 Mars）距离太阳比水星远，它们的公转轨道都比水星长。

4. Which planet has a thick atmosphere mainly composed of carbon dioxide?A. EarthB. MarsC. VenusD. Jupiter答案：C。

解析：金星（Venus）有一层非常厚的大气层，其主要成分是二氧化碳 carbon dioxide）。

地球 Earth）的大气层主要由氮气和氧气等组成；火星（Mars）大气层很稀薄，主要成分虽然有二氧化碳但比例和金星不同；木星（Jupiter）的大气层主要由氢和氦等组成。

The Globular Cluster System of NGC 1316 (Fornax A)

a r X i v :a s t r o -p h /0103501v 1 29 M a r 2001Astronomy &Astrophysics manuscript no.(will be inserted by hand later)The Globular Cluster System of NGC 1316(Fornax A)M.G´o mez 1,2,T.Richtler 3,L.Infante 1,and G.Drenkhahn 41Departamento de Astronom ´ıa y Astrof ´ısica,P.Universidad Cat´o lica de Chile.Casilla 306,Santiago,Chilee-mail:mgomez@astro.puc.cl,linfante@astro.puc.cl 2Sternwarte der Universit¨a t Bonn,Auf dem H¨u gel 71,D-53121Bonn,Germany 3Departamento de F ´ısica,Universidad de Concepci´o n.Casilla 4009,Concepci´o n,Chile e-mail:tom@coma.cfm.udec.cl 4Max-Planck-Institut f¨u r Astrophysik,Postfach 1317,D-85741Garching bei M¨u nchen,Germany e-mail:georg@mpa-garching.mpg.deReceived .../Accepted ...Abstract.We have studied the Globular Cluster System of the merger galaxy NGC 1316in Fornax,using CCD BV I photometry.A clear bimodality is not detected from the broadband colours.However,dividing the sample into red (presumably metal-rich)and blue (metal-poor)subpopulations at B −I =1.75,we ﬁnd that they follow strikingly diﬀerent angular distributions.The red clusters show a strong correlation with the galaxy elongation,but the blue ones are circularly distributed.No systematic diﬀerence is seen in their radial proﬁle and both are equally concentrated.We derive an astonishingly low Speciﬁc Frequency for NGC 1316of only S N =0.9,which conﬁrms with a larger ﬁeld a previous ﬁnding by Grillmair et al.(1999).Assuming a “normal”S N of ∼4for early-type galaxies,we use stellar population synthesis models to estimate in 2Gyr the age of this galaxy,if an intermediate-age population were to explain the low S N we observe.This value agrees with the luminosity-weighted mean age of NGC 1316derived by Kuntschner &Davies (1998)and Mackie &Fabbiano (1998).By ﬁtting t 5functions to the Globular Cluster Luminosity Function (GCLF),we derived the following turnover magnitudes:B =24.69±0.15,V =23.87±0.20and I =22.72±0.14.They conﬁrm that NGC 1316,in spite of its outlying location,is at the same distance as the core of the Fornax cluster.Key words.galaxies:distances and redshifts –galaxies:elliptical and lenticular,cD –galaxies:individual:NGC 1316–galaxies:interactions1.IntroductionThe analysis of globular cluster systems (GCSs)in ellipti-cal galaxies can have diﬀerent motivations.One of them is to investigate the variety of GCS morphologies in relation to their host galaxy properties in order to gain insight into the formation of cluster systems (see Ashman &Zepf 1997and Harris 2000for reviews).On the other hand,GCSs have been successfully em-ployed as distance indicators (Whitmore et al.1995,Harris 2000).This is particularly interesting if the host galaxy is simultaneously host for a type Ia supernova whose ab-solute luminosity can accordingly be determined,as has been the case for SN 1992A in NGC 1380(Della Valle et al.1998)and SN 1994D in NGC 4526(Drenkhahn &Richtler 1999).However,it can happen that both aspects are equally interesting as with the target of the present contribution,NGC 1316.2M.G´o mez et al.:The Globular Cluster System of NGC1316(Fornax A)during a merger event.But despite the strong evidence for a previous merger in NGC1316,the only indication for cluster formation is that Grillmair et al.(1999,here-after Gr99),could not see a turnover in the GCLF at the expected magnitude.They interpreted thisﬁnding as an indication for an enhanced formation of many less massive clusters,perhaps in connection with the merger.However, their HST study was restricted to the innermost region of the galaxy.In contrast to other galaxy mergers,where,presum-ably caused by the high star-formation rate(Larsen& Richtler1999,2000),the speciﬁc frequency of GCs in-creases,Gr99found an unusually small total number of clusters relative to the luminosity of NGC1316(M V∼−22.8,adopting a distance modulus to Fornax ofµ= 31.35,Richtler et al.2000).There is also evidence from stellar population synthesis of integrated spectra that NGC1316hosts younger popu-lations(Kuntschner&Davies1998,Kuntschner2000)and thus the question arises,whether the surprisingly low spe-ciﬁc frequency is caused by a high luminosity rather than by a small number of clusters.Goudfrooij et al.(2000, hereafter Go00)obtained spectra of27globular clusters and reported that the3brightest clusters have an age of about3Gyr,indicating a high star-formation activity 3Gyr ago,presumably caused by the merger event.Theseﬁndings and the hope for a good distance via the GCLF were the main motivation to do the present study of the GCS of NGC1316in a larger area than that of the HST study.As we will show,this galaxy resembles in many aspects the“old”merger galaxy NGC5018,whose GCS has been investigated by Hilker&Kissler-Patig(1996).The paper is organized as follows:in Sect.2we dis-cuss the observations,the reduction procedure and the selection of cluster candidates.The photometric and mor-phological properties of the GCS are discussed in Sect.3. Sect.4contains ourﬁndings concerning the Speciﬁc Frequency.We conclude this work with a general discus-sion in Sect.5.2.Observations and ReductionThe B,V and I images were obtained at the3.6m tele-scope at La Silla during the nights29th and30th of December,1997(dark moon),using the ESO Faint Object Spectrograph and Camera,EFOSC2.Theﬁeld of view was 5.′6×5.′6with a scale of0.′′32/pixel.During theﬁrst night, short-and long-exposures in eachﬁlter were centred on the galaxy.In the second night,a backgroundﬁeld located about5′away from the centre of NGC1316was observed, overlapping by1′the observations of theﬁrst night.In addition,severalﬁelds containing standard stars from the Landolt catalog(Landolt1992)were acquired in eachﬁl-ter,as well as some short exposures of NGC1316.Fig.1 shows the combined frames from both nights and Table1 summarises the observations.Table1.Summary of the observations.Dec.29,1997B4×6001.′′1Dec.29,1997V5×3001.′′0Dec.29,1997I6×3001.′′0Dec.30,1997B4×6001.′′3Dec.30,1997V3×6001.′′3Dec.30,1997I3×6001.′′2M.G´o mez et al.:The Globular Cluster System of NGC1316(Fornax A)3 Table2.General parameters of the target galaxy,from de Vaucouleurs et al.(1991)and Poulain(1988).NGC131603h22m41.s6−37◦06′10′′240.◦16−56.◦69(R’)SAB(s)08.53±0.080.861793±12ﬁlter A j1A j2rms of theﬁtture radii between22.′′9and86.′′6are: ∆V =0.013,∆B−V =0.007and ∆V−I =0.006mag,well below therms of theﬁt(see Table3).We then deﬁned5local stan-dard stars in theﬁeld of NGC1316to set the photometryof both nights in a consistent way.2.3.Selection criteriaSeveral criteria have been applied to select cluster can-didates,according to colours,magnitude,photometric er-rors,stellarity index and projected position around thegalaxy.We assume that the clusters are similar to theMilky Way clusters.Adopting an absolute turnover mag-nitude(TOM)of V=−7.60for the galactic clusters(Drenkhahn&Richtler1999,Ferrarese et al.2000)andµ=31.35(Richtler et al.2000),the TOM of NGC1316isexpected to be V∼23.7mag,and the brightest clustersabout V∼20.Although no reddening corrections are normally ap-plied when looking towards Fornax(Burstein&Heiles1982),we cannot restrict the colours of the clusters inNGC1316to match exactly the galactic ones.One pointis the smaller sample of galactic clusters.Besides,we mustallow for signiﬁcant photometric errors of faint cluster can-didates.Fig.2shows a colour-magnitude diagram for allobjects detected simultaneously in B,V and I in bothnights(before the selection),together with the cut-oﬀval-ues adopted as criterium for this colour.As can be seen,the majority of objects have colours around V−I=1.0.Objects bluer than0.5mag are very probably foregroundstars.A fraction of the data points redder than V−I=1.6are background galaxies.We also tested in our images the robustness of the“stellarity index”computed by SExtractor.This indexranges from0.0(galaxy)to1.0(star)and varies for thesame object by about0.2when classifying under diﬀerentseeing conditions,except for the brightest objects,whichare clearly classiﬁed.By visual inspection of the images,we are quite conﬁdent that bright galaxies are always givenindices near to zero.However,this classiﬁcation becomesprogressively more diﬃcult with fainter sources.4M.G´o mez et al.:The Globular Cluster System of NGC 1316(Fornax A)−0.50.51 1.522.5V−I161820222426V Fig.2.A colour-magnitude diagram for all objects de-tected in B ,V and I in both nights before the selection criteria (911points).The dashedlines indicates the selection criterium in the V −I colour (see Sect.2.3.)V0.00.20.40.60.81.0s t e l l a r i t y i n d e xFig.3.The stellarity index computed by SExtractor as function of the V magnitude.The dashed lined indicates the cut value adopted in the selection criteria to reject background galaxies.Fig.3shows the “stellarity index”for the 911objects in our sample (before the selection criteria)as a function of the magnitude.Two groups of objects having indices of ∼0.0and ∼1.0can be seen,but it is apparent that faint clusters cannot be unambiguously distinguished from background galaxies due to the uncertainty of the stellar-ity index in the case of faint sources.Very similar results were obtained with our “artiﬁcial stars”(see Sect.2.5),where indices down to 0.2were measured for faint objects that are constructed using the PSF model and,therefore,are expected to have a stellarity index of ∼1.0.Guided by our experience with artiﬁcial stars,we de-ﬁned the cut-oﬀvalue for the stellarity index to be 0.35.Remaining galaxies will be statistically subtracted be-cause the same criteria are applied to the background ﬁeld (see Sect.2.4).Finally,we rejected objects with photometric errorlarger than 0.15mag.To summarise,the following criteria were applied to our sample of 911sources detected in B ,V and I :i)V >19.5ii)0.4<B −V <1.4iii)0.3<V −I <1.8iv)stellarity index >0.35v)error(V ),error(B −V ),error(V −I )<0.15375objects met this set of criteria and are our globular cluster candidates.2.4.Background correctionAfter the selection,there might still be some contamina-tion by foreground stars and background galaxies in our sample.To subtract them statistically,one needs to ob-serve a nearby ﬁeld,where no clusters are expected,and to apply the same detection and selection criteria as with the galaxy frame.However,the analysis of our background ﬁeld still shows a concentration towards the galaxy centre,which means that only part of the ﬁeld can be considered as background.We used the radial proﬁle of the GC surface densi-ties (see Sect.3.3)to select all objects on the ﬂat part of the proﬁle,i.e.,where the number of globular cluster can-didates per area unit exhibits no gradient.Fig.11(top)shows that this occurs at r ≈300′′,where r is the distance from the optical centre.Thus,all objects with galactocen-tric distances larger than 300′′and matching the above criteria,constitute our background sample.We constructed a semi-empirical luminosity function of the background clusters with a technique described by Secker &Harris (1993),where a Gaussian is set over each data point,centred at the corresponding observed magni-tude.The sum of all Gaussians gives a good representation of the background,without introducing an artiﬁcial undu-lation or loss of information due to the binning process.Fig.4shows the histogram of the background objects,us-ing a bin size of 0.4mag,and the adopted semi-empirical function,which we use as background in the calculation of the luminosity function (see Sect.3.4)and the speciﬁc frequency.Admittedly,the numbers are small.The dip at V =23may be simply a result of bad statistics.On the other hand,as Table 6shows,the background counts are small compared to the clusters counts.Therefore,errors of the order of the statistically expected uncertainty do not signiﬁcantly inﬂuence our results and are accounted for in the uncertainties of the total counts in Table 6.pleteness correctionTo correct statistically for completeness,one needs to de-termine which fraction of objects are actually detected by the photometry routines.These ‘artiﬁcial stars ex-periments’were performed using the task addstar inM.G´o mez et al.:The Globular Cluster System of NGC 1316(Fornax A)52021222324V05101520N Fig.4.The semi-empirical luminosity function for the background ﬁeld (dashed line).A histogram with a bin size of 0.4mag is over-plotted for comparison.DAOPHOT.In one step,100stars were added in the sci-ence frames from V =20to V =25in steps of 0.1mag,distributed randomly to preserve the aspect of the image and not to introduce crowding as an additional param-eter,but with the same coordinates in the B ,V and I frames every loop.The colours of the stars were forced to be constant B −V =0.7and V −I =1.0,close to the mean colours of the globular clusters in NGC 1316(see Sect.3.1).The object detection,photometry,classi-ﬁcation and selection criteria were applied in exactly the same way as for the globular cluster candidates.To get suﬃciently good statistics,we repeated the whole proce-dure 10times,using diﬀerent random positions in each of them and averaging the results.In all,50000stars were added.However,the completeness is not only a function of the magnitude.Due to the remaining noise after galaxy subtraction,the probability of detecting an object near the centre of the galaxy is smaller than in the outer parts.We divided our sample of artiﬁcial stars into elliptical rings,in the same way as we did in deriving the radial proﬁle (see Sect.3.3).The results of the completeness tests are summarised in Fig.5.It can be seen that the 50%limit goes deeper with increasing galactocentric distance.3.Photometric and morphological properties 3.1.Colour distributionIn this section we discuss the colours of our GC candidates.No interstellar reddening is assumed (Burstein &Heiles 1982)and therefore,only internal reddening might aﬀect the colours.The histograms in Fig.6show the colour distribution of the cluster candidates.A ﬁt of a Gaussian function with free dispersions returned the values listed in Table 4and is overplotted for comparison.As can be seen,the dispersion in the B −V and V −I histograms is completely explained by the photometric er-rors alone.This is not the case for the B −I histogram,due probably to the greater metallicity sensitivity of thisV0.00.20.40.60.81.0c o m p l e t e n e s spleteness factors in four elliptical annuli.The probability of detection strongly decreases near the centre of NGC 1316.Table 4.Fit of a Gaussian function to the colour his-tograms of the GC candidates.B −V 0.80±0.020.13±0.04V −I 0.95±0.010.17±0.02B −I 1.77±0.020.35±0.036M.G´o mez et al.:The Globular Cluster System of NGC 1316(Fornax A)0.00.51.0 1.52.0B−V0204060N0.00.51.0 1.52.0V−I0204060N0.81.31.82.3 2.8B−I010203040N Fig.6.Colour histograms of the cluster candidates.The bin size is 0.05mag in each colour.A Gaussian function has been ﬁt to the histograms (dashed line,see text).The dot-dashed line is a Gaussian with σ=0.15.The long-dashed line at B −I =1.75(lower panel)was set to divide the sample in red and blue clusters.the clusters are on average ∼0.2mag bluer than the un-derlying galaxy light.This is a property commonly found also in normal early-type galaxies,where the blue and presumably metal-poor clusters indicate the existence of−3.0−2.0−1.00.0 1.0[Fe/H]1020304050NFig.7.Metallicity histogram of the GCS of NGC 1316,from its B −I broadband colour.The galactic system (dashed line)is overplotted for comparison.The long-dashed line near [Fe /H]=−1.0divides the sample in metal-rich and metal-poor clusters,using the calibration from Couture et al (1990)and B −I =1.75(see text and Fig.6.)a faint metal-poor stellar (halo?)population,as the case of NGC 1380suggests (Kissler-Patig et.al 1997).However,the non-existence of a colour gradient is consistent with the ﬁnding that blue and red clusters have similar surface density proﬁles (Sect.3.3).Diﬀerential reddening caused by the irregular dust structure might aﬀect the width of the colour distribution,but apparently does not produce any colour gradient.3.2.Angular distributionFor all objects in our sample of clusters,a transformation from cartesian (x,y )coordinates to polar (r,θ)was done,with origin in the optical centre of NGC 1316.An oﬀset of 50◦in θwas applied to match the PA of the galaxy quoted by RC3.In this way,θ=0represents the direction of the semi-major axis (sma)of the galaxy,a ,and θ=90◦the direction of b ,the semi-minor axis.To analyse the angular distribution,we rejected ob-jects inside a radius of 150pixels (corresponding to 4.3kpc with µ=31.35),where the completeness is signiﬁcantly lower (see Fig.5)and some clusters appear over ripples and dust structures.Objects outside of 450pixels were also rejected,as one needs equally-sized sectors to do this analysis,and r =450is roughly the radius of the largest circle fully covered by our frame (see dotted line in Fig.10).Only candidates brighter than V =23.8(the 50%completeness level in the entire frame)were considered.The data were then binned in θ.Several bin sizes from 18◦to 30◦were tested,and Fig.9shows the histogram for a bin size of 22.◦5,which corresponds to dividing the sample into 16sectors.The bins were taken modulo πfor a better statistics,that is,we assume that the distribution of clusters is symmetric along the semi-mayor axis of the galaxy.Due to the substructures present in NGC 1316,andM.G´o mez et al.:The Globular Cluster System of NGC 1316(Fornax A)71.21.4 1.61.82.0 2.2 2.4log r (arcsec)1.02.03.0B −I1.02.03.0B −IFig.8.The B −I colour gradient along the projected galactic radius.Top:the cluster candidates and a least-square ﬁt(solid line).The crosses indicate the B −I colour of the galaxy.Bottom:the mean colour in several rings,with the error bars indicating the σof the mean at that ring.090180270360θ [deg]10203040N Fig.9.The angular distribution of globular clusters for a radius from 150to 450pixels (48′′to 144′′)down to V =23.8.The bin size is 22.◦5and the data were taken mod π.The histogram from 0◦to 180◦is repeated from 180◦to 360◦for a better visualisation.The dashed line indicates the best ﬁt of a double-cosine function.from the fact that it is a merger galaxy,one could expect some systematic diﬀerences in the azimuthal distribution of the clusters between both halves.Although this is not observed at any bin size,the small number of counts does not allow us to address this question clearly.The histogram shown in Fig.9demonstrates the strong correlation of the globular clusters with the galaxy light.By ﬁtting isophotes to the galaxy,we obtained ellipticities ranging from 0.27to 0.32and position angles from 49◦to53◦,between semi-major axes of 150to 450pixels (thesame used with the clusters).From the least-square ﬁt to this histogram (with ﬁxed period π),we derived PA =63◦±9◦and an ellipticity of 0.38±0.06.There are,however,some problems that cannot be eas-ily resolved with our ground-based data.As indicated,the detection of cluster candidates near the centre of the galaxy is quite poor.This is,unfortunately,the most in-teresting region to search for young clusters which might be related to a merger event.3.3.Radial proﬁleTo derive the radial surface density of GCs,we divide our sample into elliptical annuli,as shown in Fig.10.The annuli have a width of 100pixels along the major axis (a )and start from a =50pixels.Due to the small number of objects in the periphery of NGC 1316,rings beyond a =900were given a width of 300pixels.The ellipticity,position angle and centre of these rings were taken from the ﬁt of the galaxy light (see Sect.3.2)and ﬁxed for all annuli.In particular,the ellipticity e ,deﬁned as 1−(b/a ),where a and b are the semi-major and semi-minor axis respectively,was set to 0.3and the PA to 50◦.We then counted the number of globular cluster can-didates per unit area in each ring,down to V =23.8,and corrected them with the corresponding completeness function.The results are presented in Table 5.The ﬁrst column lists the mean semi-major axis of the ring.Column 2gives the raw number of clusters down to V =23.8,without correction for completeness.Column 3lists the corrected data with their errors.Column 4lists the visible area of the rings,in ⊓⊔′.Column 5gives the number of candidates per unit area.Column 6,7and 8are used to compute the Speciﬁc Frequency (see Sect.4).Fig.11shows the radial proﬁle of the clusters’surface density,before and after the subtraction of the background counts.A ﬁt of a power-law ρ(r )=A ·r α,where ρis the surface density and r the projected distance along the semi-major axis,gives αgcs =−2.04±0.20and αgal =−2.03±0.02for the clusters and the galaxy light,respectively.We are well aware that a King proﬁle may be more adequate than a power function,but our purpose is to compare our result with previous work in other GCSs in Fornax,which quote only power functions.The similarity between both slopes indicates that the GCS of NGC 1316is not more extended than the galaxy light.Moreover,αGCS =−2.04is in good agreement with other GCS of “normal”early-type galaxies in Fornax (Kissler-Patig et al.1997).We divided the system at B −I =1.75mag into blue (presumably metal-poor)and red (metal-rich)clusters,and searched for systematic diﬀerences in the morpholog-ical properties between both subgroups.Again,only clus-8M.G´o mez et al.:The Globular Cluster System of NGC1316(Fornax A)Table5.This table gives the result of the radial proﬁle of the cluster candidate surface density.Theﬁrst column lists the centre of each annulus(in pixels).Then follows the raw number counts down to V=23.8,before and after the correction for completeness.The fourth column gives the visible area of the annulus in⊓⊔′.Column5lists the mean density of GC per⊓⊔′.Columns6and7give the number of clusters down to the TOM in V,before and after the correction for completeness.The applied geometrical corrections are listed in column8.Finally,the number of the clusters in each annulus,after doubling the counts around the TOM.Note that the corrected and total number of clusters for the innermost annulus(sma=100)are NOT derived using the completeness correction.Instead,they were estimated by extrapolating the radial proﬁle towards the centre(see text in Sect.4).1002058.6±18.1 1.25146.86±14.4720200.2±37.5 1.400±7520053100.3±17.9 2.50240.09±7.1553100.7±18.0 1.201±3630068104.4±15.2 3.75127.84±4.0569109.4±15.8 1.219±324005465.4±10.7 5.00613.06±2.135668.9±11.0 1.134±225004858.2±10.0 6.2349.34±1.605162.0±10.40.997124±216003742.9±8.5 6.1596.96±1.223744.5±8.80.821108±217001922.4±6.2 5.1454.35±1.211922.8±6.30.58878±219001923.2±6.49.4402.45±0.68————12001112.7±4.67.1591.77±0.64————150045.3±3.2 2.8801.84±1.11————M.G´o mez et al.:The Globular Cluster System of NGC 1316(Fornax A)9Fig.10.The elliptical annuli used in the calculation of the globular cluster density and speciﬁc frequency.The open circles indicate the position of all GC candidates brighter than V =23.8.Objects outside the annulus deﬁned by r =150and r =450pixels (dotted line)were rejected for the analysis of the angular distribution (see Sect.3.2).Objects outside the dashed ellipse are considered as background.The scale and orientation is the same as in the Fig.1.There are two additional columns,namely the number of blue and red clusters.They were calculated in the same way and will be discussed in Sect.5.Bin sizes of 0.3,0.4and 0.5mag were tested,and the results were always in good agreement with each other.Finally,we have chosen 0.5mag as our bin size from the appearance of the ﬁt histogram,and the absence of undu-lations which are present for the other cases.We note,however,that our derived TOM is close to the limit of the observations,and the last bins are strongly aﬀected by the completeness correction.Nevertheless,the similarity of the results using diﬀerent bin sizes and cen-ters,and the robustness of the ﬁt against skipping the last bin,is encouraging.100110100G C /a r c m i n2100r (arcsec)110100G C /a r c m i n2Fig.11.Top:the radial proﬁle of the density of glob-ular cluster candidates.The dashed line indicates thevalue adopted for the background,corresponding to 2.0objects /⊓⊔′.Bottom:the radial proﬁle after subtrac-tion of the background counts.The crosses represent the proﬁle of the galaxy light,arbitrarily shifted.1.61.82.02.2 2.4log r (arcsec)−0.50.00.51.01.52.0l o g (G C /a r c m i n2)Fig.12.The radial proﬁle of the GC surface density for the red (triangles)and blue population (squares).No sys-tematic diﬀerence is seen and both are equally concen-trated.Fig.14shows the three luminosity functions in B ,V ,I .For ﬁtting the LF we chose t 5functions,which are of the form:t 5(m )=85πσt1+(m −m 0)210M.G´o mez et al.:The Globular Cluster System of NGC1316(Fornax A)Table6.The counts(in bins of0.5mag)used in the determination of the GCLF.Given are the V-magnitudes(or B,I,respectively)of the bin centers.Then follow the raw counts of the four elliptical annuli N i(see text)together with the corresponding completeness factors f i.The background counts are then listed as deﬁned in Sect.2.4.The completeness factors of the fourth annulus have been used for the background as well.The total number of clusters is the sum of the four annuli minus the background,normalised to the same area(see text).Also given is the number of clusters for the blue and the red population separately,where the separating colour was B−I=1.75.19.500.7110.981 1.002 1.000.04.0±2.01.0±1.03.0±1.720.010.7110.983 1.001 1.000.06.4±2.72.4±1.74.0±2.020.510.6700.984 1.002 1.000.26.9±3.13.9±2.63.0±1.721.020.6260.983 1.003 1.00 1.012.6±5.01.4±3.311.2±3.821.520.5830.94120.9970.99 2.518.8±7.07.8±4.611.3±5.222.020.5650.84140.97110.98 4.622.2±8.814.4±6.98.0±5.422.570.40110.68320.95140.95 4.269.8±12.536.6±9.033.3±8.623.030.35180.54390.93140.90 1.794.2±12.944.3±8.749.9±9.523.520.1480.28520.71190.79 3.7127.2±19.965.5±15.661.7±12.124.000.0720.20320.2280.25 3.8145.1±38.848.8±24.896.5±28.124.500.0000.0040.0310.030.5———B N B1f1N B2f2N B3f3N B4f4N B bkg.N B total N B blue N B red18.500.7110.980 1.002 1.000.03.0±1.70.0±0.03.0±1.719.000.7110.984 1.001 1.000.06.0±2.51.0±1.05.0±2.219.530.6710.983 1.000 1.000.08.5±3.34.0±2.34.5±2.320.000.6350.983 1.005 1.000.511.7±4.13.2±2.58.5±3.320.540.5840.94110.9950.99 2.819.8±7.49.5±4.910.3±5.521.020.5660.84160.97100.98 3.826.7±8.59.3±5.417.4±6.621.540.4090.68350.95170.95 5.163.1±12.133.0±9.030.1±8.022.050.35180.54370.93120.90 1.994.9±13.539.0±9.255.9±9.822.510.1490.28460.71150.79 2.3115.0±17.962.0±13.953.4±10.923.010.0700.20380.22150.25 4.3199.4±45.4130.6±36.468.8±24.623.500.0210.0030.0300.03 1.4———。

Non-linear generation of warps by spiral waves in galactic disks

2
F. Masset & M. Tagger: Excitation of warps by spiral waves in galaxies by non-linear coupling
linear coupling is weak at such small relative amplitudes. However in the above-mentioned works it was found that the presence of resonances could make the coupling much more eﬃcient if the wave frequencies are such that their resonances (i.e. the corotation of one wave and a Lindblad resonance of another one) coincide. At this radius the non-linear terms become comparable with the linear ones, so that the waves can very eﬃciently exchange energy and angular momentum. Indeed in Sellwood’s (1985) simulations, as discussed by Tagger et al. (1987) and Sygnet et al. (1988), an “inner” spiral or bar wave, as it reaches its corotation radius, transfers the energy and angular momentum extracted from the inner parts of the disk to an “outer” one whose ILR lies at the same radius, and which will transfer them further out, and ultimately deposit them at its OLR. In this process the energy and momentum are thus transferred much farther radially than they would have been by a single wave, limited in its radial extent by the peaked rotation proﬁle. We will show here that a similar mechanism, now involving one spiral and two warp waves is not only possible (by the “selection rules” associated with their parity and wavenumbers), but also very eﬃcient if the same coincidence of resonances occurs. This allows the spiral wave, as it reaches its OLR (and from linear theory deposits the energy and momentum extracted from the inner regions of the disk) to transfer them to the warps which will carry them further out. Unlike Tagger et al. (1987) and Sygnet et al. (1988), we will throughout this paper restrict our analysis to gaseous rather than stellar disks, described from hydrodynamics rather than from the Vlasov equation. The reason is that our interest here lies mainly in the excitation of the warps, which propagate essentially in the gas (indeed the outer warp is observed in HI, and the corrugation is most likely (Florido et al. 1991) due to the motion of the gaseous component of the galactic disk). On the other hand, the spiral wave propagates in the stellar as well as the gaseous disk. The diﬀerence is important only in the immediate vicinity of Lindblad resonances, where the spiral wave is absorbed; as a consequence, its group velocity vanishes at the resonances. Since the group velocity of the waves will appear as an important parameter, we will choose to keep the analytic coupling coeﬃcient derived from the hydrodynamic analysis, but we will introduce, for the spiral density wave, the group velocity of a stellar spiral. From the physics involved this will appear as a reasonable approximation; furthermore it should only underestimate the coupling eﬃciency, since it does not include the resonant stellar motions near the resonance. On the other hand, we will show that non-linear coupling is eﬃcient only in a narrow annulus close to the OLR of the spiral, over a scale length similar to the one of Landau damping. We will thus conclude that the two processes are in direct competition, with the spiral transferring its energy and momentum, in part to the stars by Landau

Color-Magnitude Diagram Distribution of the Bulge Red Clump Stars - Evidence for the Galact

a rXiv:as tr o-ph/94426v115Apr1994COLOR-MAGNITUDE DIAGRAM DISTRIBUTION OF THE BULGE RED CLUMP STARS –EVIDENCE FOR THE GALACTIC BAR K.Z.Stanek 1Princeton University Observatory,Princeton,NJ 08544–1001e-mail I:stanek@ M.Mateo Department of Astronomy,University of Michigan,821Dennison Bldg.,Ann Arbor,MI 48109–1090and A.Udalski,M.Szyma´n ski,J.Ka l u˙z ny,M.Kubiak Warsaw University Observatory,Al.Ujazdowskie 4,00–478Warszawa,Poland ABSTRACT The color-magnitude diagrams of ∼5×105stars obtained for 13ﬁelds towards the Galactic bulge with the OGLE project reveal a well-deﬁned population of bulge red clump stars.We ﬁnd that the distributions of the extinction-adjusted apparent magnitudes of the red clump stars in ﬁelds lying at l =±5◦in galactic longitude diﬀer by 0.37±0.025mag .Assuming that the intrinsic luminosity distribution of the red clump stars is the same on both sides of the Galactic center,this implies that the distances to the red clump stars in the two ﬁelds diﬀer by a factor of 1.185±0.015.A plausible explanation of theobserved diﬀerence in the luminosity distribution is that the Galactic bulge is a triaxial structure,or bar,which is inclined to the line of sight by no more than 45◦,with the part of the bar at the positive galactic longitude being closer to us.This agrees rather well with other studies indicating the presence of the bar in the center of the Galaxy.Color-magnitude diagram data are accessible over the computer network with anonymous ftp .Subject headings:stars:HR diagram –stars:statistics –galaxy:general –galaxy:structure1.INTRODUCTIONThe Optical Gravitational Lensing Experiment(OGLE,Udalski et al.1992,1993b, 1994)is an extensive photometric search for the rare cases of gravitational microlensing of Galactic bulge stars by foreground stars,brown dwarfs and planets.It provides a huge data base(Szyma´n ski&Udalski1993),from which color-magnitude diagrams have been compiled(Udalski et al.1993a).These color-magnitude diagrams reveal an expected population of bulge stars,with its turn-oﬀpoint,red giant branch and red clump,and also an unexpected concentration of stars in the blue part of the color-magnitude diagrams, which was recently explored in detail by Paczy´n ski et al.(1994).In this paper we use the well-deﬁned population of red clump stars to investigate the presence of a triaxial structure, or bar,in the bulge of the Galaxy.A number of recent studies show unambiguously the presence of such a structure in the center of the Galaxy.Blitz&Spergel(1991)analyzed2.4µm observations of the Galactic center of Matsumoto et al.(1982)and showed convincingly that the observed asymmetry in the galactic longitude distribution of surface brightness is naturally explained by the bar with the near side in theﬁrst Galactic quadrant.They also argue that there is a small tilt of the bar with respect to the Galactic plane,consistent with the tilt proposed by Liszt& Burton(1980)from21cm emission kinematics.Binney et al.(1991)have constructed a dynamical model for the HI,CO and CS emission in the inner Galaxy,and their resulting bar has the same orientation as that suggested by Blitz&Spergel(1991)in the sense that the closer part of the bar is at positive galactic longitudes.COBE multiwavelenght observations of the Galactic center(Weiland et al.1994)conﬁrmed the existence of the longitudinal asymmetry discussed by Blitz&Spergel(1991),but Weiland et al.argue that the signature of the tilt disappears when the Galactic center emission is corrected for absorption.There is also evidence for the triaxial structure in the center of the Galaxy from star counts.Nakada et al.(1991)analyzed the distribution of IRAS Galactic bulge stars and found asymmetry in the same sense as Blitz&Spergel(1991)and Binney et al.(1991). Whitelock&Catchpole(1992)analyzed the number distribution of Miras in the bulge as a function of distance modulus and found that the half of the bulge which is at positive galactic longitude is closer to us than the other half.The observed stellar distribution could be modelled with a bar inclined at roughly45◦to the line of sight.Weinberg(1992)used AGB stars as star tracers and mapped the Galaxy inside the solar circle.He found evidence for a large stellar bar with semimajor axis of≈5kpc and inclination placing the nearer side of the bar at positive galactic longitudes.Spergel(1992)gives a detailed account of the evidence for the bulge being barred.2.THE DATAUdalski et al.(1993a)present color-magnitude diagrams(CMDs)of14ﬁelds in the direction of the Galactic bulge,which cover nearly one square degree and contain about 5×105stars.All observations were made using the1meter Swope telescope at the Las Campanas Observatory,operated by the Carnegie Institution of Washington,and a 2048×2048pixel Ford/Loral CCD detector with the pixel size0.44arcsec covering15′×15′ﬁeld of view.In this paper we discuss nineﬁelds in Baade’s Window(BW)and fourﬁelds on both sides of the Galactic center(MM5,MM7).Table1gives the coordinates of four MM ﬁelds analyzed in this paper and Figure1shows schematically the positions of all13ﬁelds in galactic coordinates.As an example,the CMD for one of the positive galactic latitude ﬁelds(MM7-A)is shown in Figure2,together with two straight lines corresponding to values of11.5and13.0for the extinction-insensitive parameter VV−I(cf.eq.1in this paper). Most of the diagram is dominated by bulge stars,with red clump stars lying approximately between the two lines shown.The part of the diagram dominated by the disk stars was recently analyzed by Paczy´n ski et al.(1994).In this paper we use well-deﬁned population of bulge red clump stars to investigate the presence of the bar in the center of the Galaxy. Red clump stars are the equivalent of the horizontal branch stars for metal rich population, i.e.relatively low mass stars burning helium in their cores.From observations and also from stellar evolution theory(Castellani,Chieﬃ&Straniero1992)we expect the bulge red clump stars to be relatively bright and have a narrow luminosity distribution with weak dependence on the metallicity.Therefore,red clump stars form a suitable population with which to investigate the structure of high-metallicity systems,like the Galactic bulge.As we observe several thousand red clump stars in eachﬁeld,we expect they can be used as a powerful tool in investigating the structure of the bulge.The part of the CMD dominated by bulge red clump stars is shown for MM5and MM7ﬁelds in Figure3,with the same two straight lines as in Figure2.It is clearly visible that the red clump stars from the MM7ﬁelds group close to the VV−I=11.5line,while red clump stars from the MM5ﬁelds have, on average,larger values of this parameter.To analyze the distribution of bulge red clump stars in a more quantitative manner,we deﬁne the extinction-insensitive VV−IparameterVV−I≡V−2.6(V−I),(1)where we use reddening law EV−I =AV/2.6,following Dean,Warren,&Cousins(1978)andWalker(1985).The parameter VV−I has been deﬁned so that if AV/EV−Iis independent oflocation then for any particular star its value is not aﬀected by the unknown extinction. It was found by Paczy´n ski et al.(1994)that the distribution of the peaks of the VV−Iparameter has deviation from the mean as small as0.03in all nine BWﬁelds,indicating that it is insensitive to the interstellar extinction,as designed.Then for all13ﬁelds we consider only the region of the CMD clearly dominated by the bulge red clump stars:15<V<19.0;1.5<V−I<2.4.(2) All stars observed in nineﬁelds in Baade’s Window,twoﬁelds in the MM5window,and two ﬁelds in the MM7window that satisﬁed the inequalities(2)were put into three separate=0.05.The result appears in Figure4,where we data sets and counted in bins of∆VV−Isee the number of stars as a function of Vfor MM7,BW and MM5.The histogram forV−Ithe red clump stars in nine BWﬁelds was scaled by dividing the total number of stars by6 as to obtain approximately equal peak number as in two MM5ﬁelds and two MM7ﬁelds. For the purpose of presentation the distributions were boxcar-smoothed with aﬁlter width of three bins.Also shown is the expected contamination of the selected CMD region by disk stars in BWﬁeld(normalized to the same area as contained by MMﬁelds),calculated using standard Bahcall&Soneira(1980)model of the galaxy.Clearly this contamination can be safely neglected.Distributions shown in Figure4are similar in shape,with red clump stars forminga pronounced peak in observed distributions.There is however a clear shift betweenthe distributions,with MM7red clump stars having on average smallest values of VV−Iparameter,with BW parameter and MM5red clump stars having largest values of VV−Istars in between.To quantify this shift in more detail,we applied the iterative bootstrap technique(for the discussion of the bootstrap method see Press et al.1992).First,we estimated the shift between the distributions by eye and we selected for all threeﬁelds the same region of distributions,which for BW7ﬁeld corresponded to11.0<V<13.5.TheV−Idistribution region of comparison was asymmetric with respect to the peak value of VV−Iwhich are contaminated by bulge red giants andso as to avoid those values of VV−Ialso,to a lesser extent,by disk stars.Then for everyﬁeld using bootstrap selected samples we estimated the mode of the distribution(Lupton1993)and obtained the shift between the distributions,which we then applied to correct the comparison region of VV−Ifor10,000Monte Carlo bootstrap selected distributions.The resulting plot of∆VV−Idata sets is shown in Figure5.Weﬁnd that the distribution of shift∆Vis veryV−I(MM5−BW)=0.15±0.02for BW and wellﬁtted by gaussian,with parameters∆VV−I(MM5−MM7)=0.37±0.025for MM7.∆VV−IThere is an additional quantity one can obtain from our data.This is the density of red clump stars for diﬀerentﬁelds.Weﬁnd that there were∼45,740red clump stars in nine BWﬁelds,∼7,280in two MM7ﬁelds and∼7,540stars in two MM5ﬁelds,satisfying inequalities(2)and falling,after shift,within the comparison region mentioned above.Thiscorresponds to a number of red clump stars perﬁeld(15′×15′)of5,080for BW,3,640for MM7,and3,770for MM5.In the following section we will discuss the implications of our observations for the structure of the Galactic bulge.3.DISCUSSIONIn previous section we have shown that the distributions of bulge red clump stars, located on both sides of the Galactic center,as a function of extinction-adjusted apparent magnitude are very similar in shape but diﬀer by substantial shift which was found to be ∆VV−I(MM5−MM7)=0.37±0.025.One possible explanation for this shift is a diﬀerence in the reddening law(see discussion following Eq.1)for diﬀerentﬁelds in the Galactic bulge.If the ratio of AV /EV−Ifor the BWﬁeld is2.6,as shown by Paczy´n ski et al.(1994),thenone needs this ratio to be about∼2.9for the MM5ﬁeld and∼2.3for the MM7ﬁeld,with exact values depending on the EV−Ivalue for BWﬁeld.Weﬁnd such a large diﬀerences rather unlikely,especially considering the small distances between theﬁelds,but we expect to address this question in more detail in the future.If we attribute the observed shift as being due to the diﬀerence in distance to the bulge red clump stars in MM5and MM7then we can obtain the ratio of distances to bothﬁelds d1/d2=1.185±0.015.If we then assume that the observed peaks in the VV−Idistributions correspond to the stars lying along major axis of the bar,we can obtain the angle of inclination of the bar to the line of sightθ≈45◦. To check how this angle corresponds to the real inclination of the bar to the line of sight, we modeled the bar with Blitz&Spergel(1991)Eq.1,taking x s=1kpc,z s=0.6kpc and changing y s from0.05to1.0kpc.We then calculated how the observed inclination changes with increasing thickness of the bar.Figure6shows the result for three values of intrinsic inclination15,30and45◦(θ=90◦corresponds to the major axis of the bar being perpendicular to the line of sight).For a bar very thin along the line of sight the inclination angle as measured corresponds directly to the true inclination angle.However,if the bar is thick then the true inclination angle is smaller than the angle measured on the basis of the mean distance to stars in theﬁelds MM5and MM7.We suspect that the tendency of the observed angle to be always greater than the intrinsic value is the generic feature of all realistic models of the bar.So,at present we can only safely state that there is substantial asymmetry in the distance to the red clump stars on both sides of the Galactic center, strongly indicating the presence of the bar in the Galactic center.Star counts can also provide very useful,direct information about space distribution of star density along the line of sight.In Figure4notice that red clump stars VV−Idistributionis relatively narrow(F W HM≈1.0mag),which gives us an upper limit for the spatial extent of bar red clump stars along the line of sight of about4kpc.To obtain more stringent limitations one needs some additional knowledge about intrinsic luminosity distribution of red clump stars.We also see that for BWﬁelds there is about40%more red clump stars than in the MMﬁelds.At the distance of Galactic center,which we assume to be8kpc,5◦corresponds to about700pc in the plane of the sky,or to about1kpc if we apply∼45◦inclination discussed above.This tells us that the bar major axis scale length is comparable to1kpc, but to obtain a better estimate for this value we need additionalﬁelds with larger values of |l|.The Galactic bar observed by COBE can still be seen at l=±15◦(Weiland et al.1994).The presence of the bar in the Galaxy seems to beﬁrmly established by various authors and methods(Blitz&Spergel1991;Binney et al.1991;Nakada et al.1991;Weinberg 1992;Whitelock&Catchpole1992;Weiland et al.1994),but there are still considerable diﬀerences as to details of the bar structure or angle of inclination to the line of sight.We have shown that the red clump stars can be very useful for investigating Galactic bar,being both numerous and relatively bright.We expect to address this problem in the future with data covering much wider range of galactic coordinates.We also note here the possibility that the Galactic bar may be associated with the deﬁciency of Galactic disk stars beyond∼3kpc from the Sun towards the Galactic bulge(Paczy´n ski et al.1994),as compared with standard models of the Galaxy.The disks of barred galaxies often show a decrease in brightness interior to the end of the bar(Kormendy1994).This eﬀect was recently observed in the near-infrared by Spillaret al.(1992)in the galaxy NGC5195.A similar decrease may exist in our Galaxy, although such a deﬁciency also occurs in inner disks of non-barred galaxies(Freeman1970; Kormendy1977).This paper and distribution of stars in the color-magnitude diagram as observedby OGLE in BW,MM5and MM7ﬁelds is available over the computer network using anonymous ftp on .Login as ftp,use your name as a password. Change directory to stanek/bar.Theﬁle read.me contains a list of the necessaryﬁles and instructions how to retrieve the data.We would like to thank B.Paczy´n ski,the PI of the OGLE project,for encouragement, many stimulating discussions and comments.We acknowledge comments from J.E.Rhoads, D.N.Spergel and N.D.Tyson,who read an earlier version of this paper,and also comments from the anonymous referee,which allowed us to improve theﬁnal version of this paper. We also acknowledge discussions with R.Lupton and J.E.Gunn.This project wassupported with the NSF grants AST9216494and AST9216830and Polish KBN grants No 2-1173-9101and BST438A/93.REFERENCESBahcall,J.N.,&Soneira,R.M.1980,ApJS,44,73Binney,J.,Gerhard,O.E.,Stark,A.A.,Bally,J.,&Uchida,K.I.,1991,MNRAS,252,210 Blitz,L.,&Spergel,D.N.,1991,ApJ,379,631Castellani,V.,Chieﬃ,A.&Straniero,O.,1992,ApJS,78,517Dean,J.F.,Warren,P.R.,&Cousins,A.W.J.,1978,MNRAS,183,569Freeman,K.C.,1970,ApJ,160,811Kormendy,J.,1977,ApJ,217,406Kormendy,J.,1994,private communicationLiszt,H.S.,&Burton,W.B.,1980,ApJ,236,779Lupton,R.,1993,Statistics in Theory and Practice,(Princeton:Princeton University Press),p.6Mihalas,D.,&Binney,J.,1981,Galactic Astronomy,(San Francisco:Freeman) Nakada,Y.,Deguchi,S.,Hashimoto,O.,Izumiura,H.,Onaka,T.,Sekiguchi,K.,& Yamamura,I.,1991,Nature,353,140Paczy´n ski,B.,Stanek,K.Z.,Udalski,A.,Szyma´n ski,M.,Ka l u˙z ny,J.,Kubiak,M.,& Mateo,M.,1994,AJ,in pressPress,W.H.,Flannery,B.P.,Teukolsky,A.S.,&Vetterling,W.T.,1992,Numerical Recipes,(Cambridge:Cambridge University Press),p.691Spergel,D.N.,1992,in The Center,Bulge,and Disk of the Milky Way,ed.L.Blitz, (Dordrecht:Kluwer Academic),p.77Spillar,E.J.,Oh,S.P.,Johnson,P.E.,&Wenz,M.,1992,AJ,103,793Szyma´n ski,M.,&Udalski,A.1993,Acta Astron.,43,91Udalski,A.,Szyma´n ski,M.,Ka l u˙z ny,J.,Kubiak,M.,&Mateo,M.,1992,Acta Astron.,42, 253Udalski,A.,Szyma´n ski,M.,Ka l u˙z ny,J.,Kubiak,M.,&Mateo,M.1993a,Acta Astron., 43,69Udalski,A.,Szyma´n ski,M.,Ka l u˙z ny,J.,Kubiak,M.,Krzemi´n ski,W.,Mateo,M.,Preston,G.W.,&Paczy´n ski,B.1993b,Acta Astron.,43,289Udalski,A.,Szyma´n ski,M.,Ka l u˙z ny,J.,Kubiak,M.,Mateo,M.,Krzemi´n ski,W.,1994, ApJL,in pressWalker,A.R.,1985,MNRAS,213,889Weiland,J.L.,et al.,1994,ApJ,425,L81Weinberg,M.D.,1992,ApJ,384,81Whitelock,P.,&Catchpole,R.,1992,in The Center,Bulge,and Disk of the Milky Way, ed.L.Blitz,(Dordrecht:Kluwer Academic),p.103FIGURE CAPTIONSFig.1.—Positions in the Galactic coordinates of13ﬁelds analyzed in this paper,for which the V−I color-magnitude diagrams were obtained by the OGLE experiment(Udalski et al.1993a,see also Table1).Fig. 2.—The V−I color-magnitude diagram for stars in the MM7-Aﬁeld of the OGLE experiment(Udalski et al.1993a).The two straight lines correspond to the value ofequal to11.5and13.0.extinction-free parameter(Eq.1)VV−IFig.3.—Region of the V−I color-magnitude diagrams dominated by bulge red clump stars for four MMﬁelds of the OGLE experiment(Udalski et al.1993a).Stars were selected to satisfy the inequalities given by Eq.2.As in Figure2,the two straight lines correspond toequal to11.5and13.0.the value of extinction-insensitive parameter VV−Idistribution for red clump stars from MM5(continuous Fig. 4.—Histograms of the VV−Iline),BW(dotted line)and MM7(short-dashed line).The histogram for the red clump stars in BW was normalized by dividing the total number of stars by6so as to obtain approximately the same peak number as in MM5and MM7.For the purpose of presentation the distributions were boxcar-smoothed with aﬁlter width of three bins.Also shown is estimated contamination from disk stars at the red clump,based on the Bahcall& Soneira(1980)model of the Galaxy(long-dashed line).shift distribution for MM7ﬁeld(continuous line)and BWﬁeld Fig.5.—Plot of the∆VV−I(dashed line)versus MM5ﬁeld.For details see text.Fig.6.—Observed angle of inclinationθobs(continuous line)as a function of bar axis ratio y s/x s.The bar was modeled using Blitz&Spergel(1991)Eq.1,withﬁxed x s=1.0kpc,z s= 0.6kpc and changing value of y s.Three values of the intrinsic inclinationθ0=15,30,45◦, shown with dashed lines,were investigated.Table1.Parameters for the four MMﬁelds ﬁeld l b CMD[◦][◦]stars。

2024年05版小学5年级上册第一次英语自测题

2024年05版小学5年级上册英语自测题考试时间：100分钟（总分:140）B卷考试人：_________题号一二三总分得分一、选择题(共计20题，共40分)1、How many legs does a crab have?A. SixB. EightC. TenD. Twelve2、选择题：What do we call the process of changing from a solid to a liquid?A. MeltingB. FreezingC. BoilingD. Evaporating3、What do we call the spiral-shaped galaxies?A. Elliptical GalaxiesB. Irregular GalaxiesC. Spiral GalaxiesD. Lenticular Galaxies4、What is the opposite of "old"?A. AncientB. NewC. RecentD. Young5、What is the name of the fairy tale character who kissed a frog?A. Snow WhiteB. CinderellaC. The Princess and the FrogD. Rapunzel6、选择题：What is the opposite of clean?A. DirtyB. NeatC. TidyD. Spotless7、选择题：What do you call an animal that only eats plants?A. CarnivoreB. HerbivoreC. OmnivoreD. Insectivore8、选择题：What do we call a person who performs magic tricks?A. MagicianB. IllusionistC. WizardD. Sorcerer9、What do you call a young snake?A. HatchlingB. PupC. KitD. Calf10、What do you use to write on paper?A. PaintB. PencilC. GlueD. Tape11、选择题：What do we call the area of land that is covered in ice?A. GlacierB. Ice capC. IcebergD. Tundra12、Which animal is known for its stripes?A. LeopardB. ZebraC. CheetahD. Tiger13、选择题：Which animal is known for its ability to change colors?A. ChameleonB. ElephantC. DogD. Cat14、Which animal is known for building dams?A. BeaverB. OtterC. RabbitD. Squirrel15、What is the main ingredient in pesto sauce?A. BasilB. ParsleyC. CilantroD. Rosemary16、选择题：What is the name of the first satellite sent into space?A. Apollo 11B. SputnikC. Voyager 1D. Hubble17、How do you say "beach" in Spanish?A. PlayaB. PlageC. StrandD. Spiaggia18、Which fruit is yellow and curved?A. AppleB. BananaC. OrangeD. Mango19、What is the name of the fairy tale character who lost her glass slipper?A. Snow WhiteB. CinderellaC. RapunzelD. Sleeping Beauty20、What do we call the act of telling the truth?A. HonestyB. IntegrityC. TransparencyD. All of the above二、听力题(共计20题，共40分)1、听力题：The teacher is ___ (kind/strict).2、听力题：My friend likes to play ____ (soccer) after school.3、听力题：The kitten is ___ with a ball. (playing)4、听力题：The _______ has beautiful flowers.5、听力题：A ______ is a large area of flat land with few trees.6、听力题：My cousin is very ____ (funny) and makes me laugh.7、听力题：A ____ has a beautiful song and cheerful chirping.8、听力填空题：I love creating videos about __________ to share with friends.9、听力题：The chemical symbol for tantalum is _____.10、听力题：The Sun's energy supports life on _______.11、听力题：The element that is a gas at room temperature and essential for life is _______.12、听力题：The capital of the Philippines is __________.13、听力题：My mom cooks ________ dinner.14、听力题：The process of changing from a liquid to a gas is called __________.I see a _____ (rabbit) in the garden.16、听力题：The flowers are ___. (blooming)17、听力题：A group of fish swimming together is called a __________.18、听力题：The ________ (garden) has many flowers.19、听力题：A mineral's crystal structure can help identify its ______.20、听力题：We play ___ (games/sports) after school.三、填空题(共计20题，共10分)1、填空题：The __________ (树) grows tall and strong in the forest.2、填空题：The tortoise moves slowly but can live for a very ________________ (长) time.3、填空题：My dad is a strong __________ (榜样) for me.4、填空题：I built a _____ (模型) of a dinosaur.5、填空题：The first manmade object to orbit the Earth was ________ (斯普特尼克).6、填空题：I enjoy playing ______ (团体运动) with my friends after school.7、填空题：My aunt loves to __________. (看书)8、填空题：We need to _______ (保持) our city clean.At the farm, there are many _______ (小鸡) pecking at the ground.10、填空题：My favorite sport is ________ (足球).11、填空题：I watched a _______ (小鸟) find food.12、填空题：The doctor, ______ (医生), checks our health every year.13、填空题：A frog's skin is smooth and ______ (湿润).14、填空题：I like to listen to _______.15、填空题：The parakeet sings _______ (悦耳) songs.16、填空题：A ____(traffic congestion) decreases urban mobility.17、填空题：The _____ (sunflower) turns towards the sun.18、填空题：The ______ (温度) can affect plant development.19、填空题：The ______ of a flower can attract different pollinators.(花的形态可以吸引不同的授粉者。

高中英语作文致力于科学热爱科学

高中英语作文致力于科学热爱科学My Love for Science and How It Makes the World BetterHi there! My name is Timmy and I'm 10 years old. I absolutely LOVE science! It's my favorite subject in school. I get so excited wheneverwe have a science lesson or experiment. To me, science is like magic, but even better because it's real!When I was really little, probably around 4 or 5 years old, I remember being completely amazed by the most simple things. Like how a seed can grow into a huge towering tree. Or how clouds can turn into rain. Or all the crazy colors you see when you shine a flashlight through a prism. Mind-blowing stuff!I was one of those kids who was always asking "why?" about everything. Why is the sky blue? Why do birds have feathers? Why do I have to go to bed at night? My poor parents probably got so tired of me bombarding them with endless questions. But I was just so curious about the world around me and desperately wanted to understand how it all works.That's why I've always loved science class so much. It gives me answers to all my "why" questions! And the more I learn, the more I want to know. Science is this amazing endless journey ofdiscovery. There's always another mystery to unravel or puzzle to solve.One of the earliest science concepts I vividly remember learning was the idea of molecules - that everything around us is made up of billions and billions of tiny building blocks called atoms that are too small to see. I mean, how cool is that?! Kind of a mind-bending fact when you really think about it. It made me look at literally everything differently, wondering what kind of molecules made up my desk, the air, a glass of water, you name it.From there, I went on to learn about other awesome science-y things like:• The life cycle of butterflies and how they go through an amazing transformation called metamorphosis• That fossils are the prehistoric remains of plants and animals that lived millions of years ago• How light travels and creates the colors we see• The three states of matter - solid, liquid and gas• Basic chemistry an d doing fun experiments like making mini volcanos with baking soda and vinegar• The planets in our solar system and how Earth is a perfect little oasis for life• The complex design and different functions of the human body...I could go on and on!To me, every new science topic I learn about is like a tiny piece of a gigantic jigsaw puzzle. And scientists are like the ultimate puzzle masters, spending their whole lives meticulously putting those pieces together to gradually uncover the bigger picture and better understand our universe. Just thinking about all the mind-blowing breakthroughs and discoveries that science has led to throughout history gives me goosebumps.Like the scientist Isaac Newton figuring out the laws of gravity after allegedly being bopped on the head by a falling apple. Or Alexander Fleming accidentally discovering penicillin, the first widely used antibiotic medication that has saved countless lives. Or the Wright brothers pioneering aviation and aerodynamics to achieve the dream of human flight. Or Marie Curie and her work in radioactivity. Or Charles Darwin and his theory of evolution by natural selection. Such revolutionary milestones that completely changed our world!And that's just scratching the surface of all the ways that science has improved our lives and expanded our knowledge.Modern societies rely on so many scientific and technological breakthroughs - like electricity, the internet, space exploration, medical treatments and surgeries, and so much more. Humans owe basically all quality of life advancements and innovations we enjoy today to the relentless efforts of scientists over many centuries.That's why I have such a deep love and respect for science and the scientists who devote their careers to constantly learning, exploring ideas and finding new discoveries. To me, they are real life superheroes! Using curiosity and intelligence instead of capes and super-strength to make the world a better place.I dream of one day becoming a scientist myself so that I can be one of the puzzle masters, conducting experiments and uncovering more secrets of how our world works. It would be simply amazing to have a career where I get paid to always be learning and satisfying my endless curiosity!There are still SO many unanswered questions and mysteries in science waiting to be solved. Like what exactly is dark matter and dark energy that makes up a huge portion of our universe? Is there life elsewhere in our galaxy or the billions of other galaxies? How did life on Earth first spark into existence? What unseen dimensions or parallel realities could exist? Whatundiscovered species are waiting to be found in unexplored corners of our planet?Those types of huge mysteries ignite my imagination and fuel my determination to study as hard as I can now so that I'll be prepared for an exciting science career later on. I want to be on the frontlines, working at big laboratories, universities or space agencies to push the boundaries of human knowledge.Whether it's finding a cure for deadly diseases, developing new renewable energy sources, inventing crazy cool future technologies or making paradigm-shifting discoveries about our universe, I want to be a part of it! Using science to directly improve human life and unlock more pieces of the cosmic puzzle sounds like the most fascinating and rewarding way I could possibly spend my life.Some kids want to be astronauts, firefighters, pilots or professional athletes when they grow up. But my dream job is to be an amazing, trailblazing scientist who changes the world in big and small ways through the power of curiosity, research and discovery!I can't wait to see what new mindblowing realizations science will uncover in the future. I feel like we've only scratched the surface of truly understanding our universe and reality itself.With so many brilliant scientists working hard every day, who knows what staggering breakthroughs and next big cosmic revelations await?!That thought alone is a huge reason why I love science so much. It's an endless frontier of limitless possibilities and surprises that constantly feed my hungry little mind. There's always another question to be answered, some new mystery to investigate, or some new idea to explore and experiment with. Science is never boring!So yeah, in case you couldn't tell already, I'm basically science's biggest fan and cheerleader over here. I sincerely believe it's one of the most important driving forces for the advancement of human civilization. Every discovery has the potential to reshape our reality and open up even more tantalizing paths for inquiry. I feel incredibly lucky to live in such an exciting era of unprecedented scientific progress.Who knows, maybe one day I'll be a famous scientist that school kids read about 50 or 100 years from now! If I keep studying hard, staying curious, and dreaming big, anything is possible. With science and imagination as my fuel and guides, the future looks brighter than one of those crazy bright pulsars in deep space. I can't wait to see what amazing places my love ofscience takes me as I keep uncovering the wonders of our wild, weird and awesome universe!。

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a r X i v :a s t r o -p h /0404164v 1 7 A p r 2004Astronomy &Astrophysics manuscript no.0932February 2,2008(DOI:will be inserted by hand later)Thick Disks of Lenticular Galaxies⋆3D-photometric thin/thick disk decomposition of eight edge-on S0galaxiesM.Pohlen 1,2,M.Balcells 1,R.L¨u tticke 3,2,and R.-J.Dettmar 21Instituto de Astrof ´ısica de Canarias,E-38200La Laguna,Tenerife,Spaine-mail:pohlen,balcells@ll.iac.es 2Astronomical Institute,Ruhr-Universit¨a t Bochum,D-44780Bochum,Germany e-mail:dettmar@astro.rub.de3Department of Computer Science,FernUniversit¨a t Hagen,D-58084Hagen,Germany e-mail:Rainer.Luetticke@FernUni-Hagen.deReceived 23December,2003;accepted 04March,2004Abstract.Thick disks are faint and extended stellar components found around several disk galaxies including our Milky Way.The Milky Way thick disk,the only one studied in detail,contains mostly old disk stars (≈10Gyr),so that thick disks are likely to trace the early stages of disk evolution.Previous detections of thick disk stellar light in external galaxies have been originally made for early-type,edge-on galaxies but detailed 2D thick/thin disk decompositions have been reported for only a scant handful of mostly late-type disk galaxies.We present in this paper for the ﬁrst time explicit 3D thick/thin disk decompositions characterising the presence and properties (e.g.scalelength and scaleheight)for a sample of eight lenticular galaxies by ﬁtting 3D disk models to the data.For six out of the eight galaxies we were able to derive a consistent thin/thick disk model.The mean scaleheight of the thick disk is 3.6times larger than that of the thin disk.The scalelength of the thick disk is about twice,and its central luminosity density between 3-10%of,the thin disk value.Both thin and thick disk are truncated at similar radii.This implies that thick disks extend over fewer scalelengths than thin disks,and turning a thin disk into a thick one requires therefore vertical but little radial heating.All these structural parameters are similar to thick disk parameters for later Hubble-type galaxies previously studied.We discuss our data in respect to present models for the origin of thick disks,either as pre-or post-thin-disk structures,providing new observational constraints.Key words.Galaxies:photometry –Galaxies:bulges –Galaxies:structure –Galaxies:fundamental parameters –Galaxies:evolution –Galaxies:formation –Galaxies:individual:ESO311-012,NGC1596,NGC2310,NGC3564,NGC3957,NGC4179,NGC4521,NGC50471.IntroductionThe knowledge of the detailed distribution of stars in galaxies is of fundamental importance to address the for-mation and evolution of those systems.To a ﬁrst approx-imation,a disk galaxy can be described by a set of dis-tinct stellar entities:a disk population,a bulge compo-nent,and a stellar halo.Deep surface photometry of ex-ternal early-type galaxies (Burstein,1979a,b,c;Tsikoudi,1979,1980)and later elaborate measurements in our own Galaxy (Gilmore &Reid,1983)revealed the need for an additional component of stars.This was called ‘thick disk’(Burstein,1979c),since it exhibiting a disk-likedistribu-2M.Pohlen et al.:Thick Disks of Lenticular GalaxiesTable1.Global parameters of the observed lenticular galaxies:(1)Principal name,(2)right ascension,(3)declination, (4)RC3coded Hubble-type,and the(5)Hubble parameter T are taken from de Vaucouleurs et al.(1991).The(6)diameter in arcminutes,the(7)heliocentric radial velocities,and the B-Band absolute magnitude(10)are taken from LEDA.According to the heliocentric radial velocities corrected for the Local Group infall into the Virgo cluster(8) from LEDA,we estimated the(9)distances following the Hubble relation with the Hubble constant from the HST key project of H0=72km s−1Mpc−1(Freedman et al.,2001).massive black holes(Lacey&Ostriker,1985),energy in-put by accretion of satellite galaxies(Carney et al.,1989; Quinn,Hernquist,&Fullagar,1993;Velazquez&White, 1999;Aguerri et al.,2001),or bar bending instabilities (Raha et al.,1991).For example,Gnedin(2003)recently used N-body simulations to show that tidal heating in a cluster is suﬃcient to thicken stellar disks by a fac-tor of2-3.This kinematic heating and vertical expan-sion will lead to a signiﬁcant morphological transforma-tion of a normal spiral galaxy into a lenticular.The third model suggests that thick disks are mostly made of de-bris material from accreted satellites.Recent cosmologi-cal N-body+SPH galaxy formation models of Abadi et al. (2003)locating the thick disk formation before z≈1ﬁnd that more than half of the thick disk stars are actually tidal debris from disrupted satellites.Therefore the thick disk is not a former thin disk thickened by a minor merger. To decide which of these hypotheses could explain the thick disk phenomenon best we needﬁrst a more general and complete statistic of thick disk properties.Naturally, these are rather global ones for external galaxies whereas our particular position in the Milky Way makes it possible to determine muchﬁner details.Since the work of Tsikoudi and Burstein(Burstein, 1979a,b,c;Tsikoudi,1979,1980)it appears well known that thick disks are quite common in S0galaxies. However,none of the more recent detections,except for two galaxies in de Grijs&van der Kruit(1996)and a short remark in de Grijs&Peletier(1997),quantify-ing detailed parameters such as the ratio of thick to thin disk scaleheight or scalelength,is actually made in S0galaxies.All these galaxies are of later Hubble type.In addition,we have not found a detailed2D thin/thick disk decomposition for any S0galaxy in the literature.Subsequent numerical decompositions deal-ing with S0galaxies after the pioneering work in the early80’s treated the thick disk either as an outerﬂat-tened but exponential halo(for NGC4452and NGC4762: Hamabe&Wakamatsu,1989),or as a spheroidal bulge component(for NGC1381:de Carvalho&da Costa, 1987)(for NGC3115:Capaccioli,Held,&Nieto,1987; Silva et al.,1989).The detections of possible halo or thick disk stel-lar light in disk galaxies of later Hubble type have been made in a scant handful of mostly nearby edge-on galaxies(e.g.for ESO342-017,IC5249, NGC891,NGC4565,NGC5907,and NGC6504: van der Kruit&Searle,1981a,b;Shaw&Gilmore,1989; Morrison,Boroson,&Harding,1994;van Dokkum et al., 1994;Sackett et al.,1994;Morrison et al.,1997; N¨a slund&J¨o rs¨a ter,1997;Lequeux et al.,1998; Zheng et al.,1999;Neeser et al.,2002).Quite recently, Dalcanton&Bernstein(2002)suggest the detection of extended,ubiquitous thick disks in a large sample of late-type,edge-on galaxies by means of multi-colour imaging. However,their thick disks are solely detected by vertical colour gradients for which dust extinction complicates the interpretation.In addition,their vertical colour proﬁles, especially(R−K),typically extend out to only very few vertical disk scaleheights.At those z-heights where they attribute the red colour to an additional component the thin disk may still be dominant over a potential thick disk and even determine the measured colour.In this paper,we analyse a set of eight edge-on S0 galaxies using the classical approach for the identiﬁcation of thick disks in external galaxies:the need for an addi-tional disk component when attempting toﬁt single disk models to the light distribution in a deep image.Thereby we characterise the presence and properties(scalelengths, -heights,and central surface brightnesses)of thick disks by directly measuring their structure.M.Pohlen et al.:Thick Disks of Lenticular Galaxies 32.Sample Selection &ObservationsThe data were taken as part of the PhD study on the ra-dial structure on galactic stellar disks by Pohlen (2001).The galaxies wereselectedaccordingtothe allocatedob-serving time,observatory,and CCD-chip size meeting the following morphological selection ing images from the Digitized Sky Survey (DSS)we veriﬁed thatthey are edge-on (i >∼86◦),undisturbed,and similar to some disk-prototypical cases like NGC 4565or IC 2531to make it possible to consistently ﬁt the applied simple disk model (cf.Sect.3).Galaxies with the following characteris-tics were rejected:spiral arms (indicating towards a lower inclination),a signiﬁcantly asymmetric or disturbed disk (indicating towards strong interaction),and two-sided or signiﬁcantly one-sided warped disks.In addition,galaxies which seemed to be dominated by the light of the bulgecomponent,or appeared to be too small (D 25>∼2′′),or showed only a faint,patchy disk were also excluded.For the observed lenticulars we therefore selected galaxies with a symmetric,smooth disk and a distinct,non-dominant bulge component.It is not unexpected that half of these galaxies show a box-or peanut-shaped (b/p)bulge com-ponent,since L¨u tticke et al.(2000a)ﬁnd that >40%of all bulges are b/p shaped.Global properties of the ﬁnally observed eight S0galaxies are given in Table 1.We do not argue that this sample is fully representative of the general population of S0galaxies but it ensures the best prospects for obtaining consistent models with our 3D modelling technique for all galaxies.The images (in Johnson R or V ﬁlter)were obtained in four observing runs in 1998/1999,three at the Danish 1.54m telescope of the European Southern Observatory (ESO,Chile)and one at the 1.23m telescope on Calar Alto (CAHA,Spain).During all three runs at the ESO the 1.54m Danish telescope was equipped with DFOSC and the C1W7/CCD which is a 2k x 2k LORAL chip providing a ﬁeld size of ≈13′and a scale of ≈0.39′′pixel −1.The run at the Calar Alto 1.23m telescope was done in service mode with the Site#18b chip,a 2048x2048SITE CCD with 24µm pixel size,providing an unvignetted ﬁeld of ≈10′and a scale of ≈0.5′′pixel −1.The standard CCD reduction techniques —overscan correction;subtraction of remaining large scale gradient in combined,oversan-subtracted,masterbias image;and careful ﬂatﬁelding–were applied using the IRAF data re-duction package.Neither the DFOSC nor the Calar Alto CCD R-band images were aﬀected by fringing.The in-dividual,dithered,reduced short exposures (150s-600s)were combined to the ﬁnal deep image using IRAF’s im-combine task.These images are rotated to the major axis using the smallest angle of rotation according to their true position on the sky.Table 2summarises the detailed obser-vational parameters.During the two ESO observing runs in 1999several Landolt (1992)ﬁelds,partly enriched with additional stars provided by B.Skiﬀ(m.),were observed.The standard ﬁelds were taken at least three times a night at diﬀerent airmasses to determine the at-mospheric extinction.During the other two observing runs no standard stars were taken.The ESO run in 1998is cal-ibrated by literature values and for galaxies without cata-logued values interpolated according to the measured sky background.Only a rough zero point could be estimated for the Calar Alto run by comparing a galaxy also ob-served in another calibrated Calar Alto run.For more de-tails about the photometric calibration we refer to Pohlen (2001).3.Extraction of the Disk Parameters 3.1.3-Dimensional Disk ModelWe have developed a semi-automatic recipe to ﬁt true 3-D single-component luminosity distributions to the 2-D data of edge-on galaxies and determine the galaxy pa-rameters,such as scalelength and scaleheight in a physi-cally meaningful way.Our method is described in detail in Pohlen et al.(2000b)and Pohlen (2001)and is only brieﬂy recalled here.The disk model is based upon the fundamen-tal work of van der Kruit &Searle (1981a).They tried to ﬁnd a ﬁtting function for the three-dimensional light dis-tribution in disks of edge-on galaxies using the empirically determined exponential radial gradient,I ∝exp(R ),and adding a description for the vertical distribution,f (z ),ofthe stars.The luminosity density distribution ˆL(R,z )can be written as:ˆL(R,z )=ˆL 0exp−R z 0f 2(z )=2sech2z z 0For any details about the numerical realisation we refer to Pohlen et al.(2000b).Therefore six free parameters(i,n,ˆL0,R co ,h,z 0)ﬁt the observed surface intensity on the CCD chip to the model.This model assumes that the vertical distribution is independent of position along the4M.Pohlen et al.:Thick Disks of Lenticular GalaxiesTable2.Observing log for the individual combined images with(1)the galaxy,(2)theﬁlter,(3)the observing date, (4)the site,(5)the total coadded on-source exposure time t int,(5)mean seeing conditions during the observations,(7)the number of individual images with their t int.major axis as is known to be true in good approximation(cf.e.g.van der Kruit&Searle,1981a;Shaw&Gilmore,1990).The increase of scaleheight with galactocentric dis-tance as reported by de Grijs&Peletier(1997)can bedescribed as a combination of two disks each with con-stant scaleheight but diﬀerent scalelength(cf.Sect.3.2).Any deviation from constant scaleheights should be visiblein the vertical proﬁles overplotted by the models,which isnot the case(cf.Appendix B).The apparent small verticalshift of some models in the lowest plotted vertical proﬁleis due to the change in radial scalelength,as described inSect.3.4.The possible inﬂuence on the six free parameters of thedust distribution,which was neglected during theﬁt,isestimated in Pohlen et al.(2000b).There we have shownthat even for a worst case scenario(large optical depthτR and a radially and vertically fairly extended dust lane)our model is able to reproduce the input parameters withan error of a typical20%.We expect this eﬀect to beeven less signiﬁcant for the present sample of lenticular,dust-depleted galaxies.Deriving individual errors on allparameters is a complex task since the main source oferror is not the numericalﬁtting procedure(<1%)butthe systematic uncertainties in the process ofﬁtting arather simple,empirical model to real galaxies.An es-timation of the errors is given in Pohlen et al.(2000b)by changing the applied boundaries of the region used toﬁt the data to the model(cf.also Pohlen,2001).Theyfound diﬀerences in h and z0of about15%andˆL0variedabout a factor of two.This is in the same range foundby Knapen&van der Kruit(1991)when they comparedpublished values of scalelength measurements from diﬀer-ent studies.3.2.Thin/thick disksPohlen(2001)noted that the S0galaxies in his sample arenot well described by any combination of a single disk andanother spheroidal component,such as a de VaucouleursR1/4bulge model(de Vaucouleurs,1948).All S0galaxiesreveal a typical,continuous change of slope when one com-pares the major axis with parallel proﬁles above/below theplane.The proﬁles signiﬁcantlyﬂatten towards cuts higherabove the midplane.According to the single componentmodelˆL(R,z)all slopes should be nearly parallel.We in-fer from the images(cf.Appendix B)that all S0galax-ies show a kind of smooth outer envelope or highlyﬂat-tened spheroidal component.This deviation from a nor-mal shape cannot be explained by a bulge component.Anylarge R1/4bulge would have to be apparent on the majoraxis which is certainly dominated by an exponential(disk)component.It is worth mentioning that in the sample ofPohlen(2001)there are four galaxies,NGC3390(T=3),NGC3717(T=3),NGC4696C(T=3.4),and NGC6504(T=2)a that showed a similar behaviour but were classi-ﬁed as late-type galaxies.The outer component could be described as a‘thickdisk’according to Burstein(1979c)with aﬂatter slopethan the inner thin disk,equivalent to a larger scalelength.However,the main characteristic of a thick disk is that theobserved vertical proﬁles depart from the simple exponen-tial pared to the model,the outer parts aresystematically brighter with increasing distance to the ma-jor axis.As mentioned by de Grijs&Peletier(1997),themeasured increase of the scaleheight with radius(‘ﬂaring’)for early-type,edge-on disk galaxies can be understood ifthese galaxies have both thick disk scalelengths and scale-heights larger than for the dominant old disk.3.3.Fitting MethodTo apply our single componentﬁtting method describedin the previous section we have to assume that there is aregion in the galaxy dominated by only one of the com-ponents.If one uses exponential proﬁles it is obvious fromthe vertical and radial cuts that there are well separatedM.Pohlen et al.:Thick Disks of Lenticular Galaxies5vertical ranges(around the major axis and the outermost proﬁles)in which the light of one of the two disks dom-inates.Fitting thin and thick disk component simultane-ously would be the desired approach.However,our sin-gle component model has already six free parameters.As shown in Pohlen(2001),ﬁtting this model to observed data is a non-trivial task.The problem is the applica-tion of an idealized model itself,which obviously will not totally accurately describe the measured two-dimensional light distribution.This technique requires continuous hu-man supervision to control the inﬂuence and quality of each individual parameter.This would most probably be even more diﬃcult for a parameter set twice as large.We decided therefore to use an iterativeﬁtting routine start-ing from outside-in since the thick disk clearly dominates the outer parts.Theﬁrst step is to determine an initial estimate for the outer disk by restricting the region to be ﬁtted and using our single component model.The next step is subtracting the derived full thick disk model from the original image andﬁt an inner disk to the residual by restricting theﬁtting range to the inner parts.Then we start from the beginning by subtracting this inner disk model from the original image andﬁt again the outer disk, now to this residual image.The initially pre-deﬁnedﬁtting regions for the thin and thick disk are sometimes adapted slightly after subtracting one of the components and be-fore starting the secondﬁtting round.As it turned out this process is remarkably stable for most of the galaxies. After one iteration the disk parameters are already the same within the range of one single model.The reason for this is the domination of the thick disk at large ver-tical z-heights(>∼3.5z n0=7h n z)measured here with high S/N,and the large radial range used toﬁt the thick disk component.To restrict the number of free parameters we decided to preﬁx the inclination during theﬁtting process for this sample.For most of the galaxies the symmetric shape of the bulge and disk component indicates an exactly edge-on orientation.Only one of the S0galaxies(NGC3957) exhibits a dust-lane making it possible to estimate the inclination at i=88◦±1◦following the method by Barteldrees&Dettmar(1994).The diﬀerent density laws for the vertical dis-tribution are similar for large z and only diﬀer around the mid-plane of the luminosity distribution (cf.Fig.4in de Grijs,Peletier,&van der Kruit,1997).In Pohlen et al.(2000b)the actual choice of oneﬁtting func-tion is done individually for each galaxy depending on the measured proﬁles.However,near the plane of the galaxy the contribution of a thick disk is much smaller than that of to the thin disk component.First tests with a free choice of theﬁtting function for the vertical den-sity distribution(exp,sech,or sech2)showed in the case of ESO311-012that the iterativeﬁt became unstable for this reason.In the subsequent modelling we have chosen the intermediateﬁtting function f2(z)∝sech(2z/z0)in all cases for the thin and thick disk component.There was only one galaxy,NGC2310,for which the sech function did not yield a satisfying convergency of the iterativeﬁt-ting.However,switching to sech2signiﬁcantly improved theﬁt.Finally,only three free parameters are left for each disk(ˆL0,h,z0).We want to point out that these decompositions are thus model dependent.An isothermal thick disk con-tributes less light to the thin/thick disk combination than to an exponential one and the shape of the thin disk will also be diﬀerent.In addition,vertical scaleheights z0ob-tained with an exp model are systematically larger than in a sech model and again larger than in a sech2ﬁt. Depending on the vertical boundaries chosen for theﬁtting these diﬀerences could be more than30%.The choice for the vertical distribution inﬂuences also the best-ﬁt scale parameter ratio z k0/z n0.Shaw&Gilmore(1989)used all combinations of either sech2or exp models for NGC4565 and derived z k0/z n0in the range of4.3−5.4.In contrast with some of the previous1-D-onlyﬁtting methods we do not simply use the deviation from a simple exponential on the minor axis,or parallel proﬁles;to mea-sure thick disks we use the full2-dimensional information and are therefore able toﬁt the radial scalelength of the thick disks.3.4.Breaks in Radial ProﬁlesOne of the main diﬃculties while properlyﬁtting our model to the S0galaxies is their outer disk structure. This will be discussed in detail in Pohlen et al.(2004) and only brieﬂy addressed here.As one can see from theﬁgures in Appendix B there are clear breaks in the outer parts of the radial proﬁles.These are simi-lar to the truncations in more later-type galaxies(cf. Pohlen et al.,2002;Kregel,van der Kruit,&de Grijs, 2002;de Grijs,Kregel,&Wesson,2001; Pohlen,Dettmar,&L¨u tticke,2000a).For all galax-ies(except ESO311-012)a similar break,slightly less pronounced,is also seen in other radial cuts parallel to the major axis.Our model,according to Eq.(1),however, describes only an inﬁnitely sharp truncation R co.As shown in Pohlen(2001)this implies a tight coupling between the radial scalelength h and the cut-oﬀradius R co,when using our modelﬁtting data with the observed breaks in the proﬁles.In addition,the sharply truncated model exhibits an intrinsic bending of the proﬁle towards the outer parts(cf.Pohlen,2001).This complicates the visual quality control compared to the moreﬂat inﬁnite exponential model without any truncation.Therefore we decided to use the inﬁnite exponential model,realised within the sameﬁtting program byﬁxing R co to ten times the radial scalelength.For our thick/thinﬁtting we restricted theﬁtting region to points inside the observed break radius.However,ﬁtting an inﬁnite exponential model to the intrinsic two-slope proﬁles is also aﬀected by systematic errors(cf.Pohlen,2001;Pohlen et al., 2004).Depending on the ratio of the inner,shallow slope (h in)up to the break,to the steeper,outer slope(h out)6M.Pohlen et al.:Thick Disks of Lenticular Galaxies beyond the break radius the determined scalelength willbe systematically too small.Assuming a mean ratio ofh in/h out=4.4±1.7from a large,edge-on sample byPohlen(2001)makes it possible to quantify the expectedoﬀset.The bestﬁtting scalelength h in will be about26%larger compared to the intrinsic radial scalelength(cf.Pohlen et al.,2004).Although the exact value of the scalelength is thusmodel dependent,neither z0norµ0are inﬂuenced by thisproblem.The derived scaleheights are independent of thescalelength and therefore robust,but of course still de-pending on the chosen density law(exp,sech,or sech2) for the z-distribution.4.ResultsFor six(75%)out of the eight S0galaxies we were able to derive consistent thick/thin disk solutions(cf.Sect.4.1). The resulting bestﬁt parameters are listed in Table 3and Table4for the thick and thin disk,respec-tively.The resulting radial and vertical proﬁles overplot-ted by our bestﬁtting model are shown in Appendix B.The derived thin disk scalelength and scaleheight values are consistent with those found in studies by Kregel,van der Kruit,&de Grijs(2002)and Pohlen (2001),containing mostly galaxies of Hubble type later than Sa.The mean ratio of thick to thin scaleheight for the ﬁve galaxies with the same vertical model combinations (sech+sech)for the thick and thin disk is z k0/z n0=3.6±1.0 and for the scalelength h k/h n=1.8±0.1.Including also NGC2310weﬁnd z k0/z n0=3.4±1.0and h k/h n=1.9±0.4. We derive central surface brightnesses(uncorrected for in-clination)in the range of22.0<∼µk0<∼22.2R-mag/2′′and 21.9<∼µk0<∼22.9V-mag/2′′for our thick disks compared to19.2<∼µn0<∼19.6R-mag/2′′and19.5<∼µn0<∼20.7V-mag/2′′for the thin disks.This implies that the contri-bution of the thick disk to the central surface brightness is about10%of that of the thin disk.The thick disk cen-tral luminosity densityˆL k0ranges between3.5%and about 10%(mean:5.6%)of the thin disk value.The ratio of the total luminosities of the thick and thin disk is between about one third and one.The proﬁle on the minor axis in addition to radial cuts high above the major axis(cf.Appendix B)reveals that for four(NGC2310,NGC3564,NGC4179,NGC5047)out of the sixﬁtted galaxies there is no signiﬁcant bulge compo-nent visible at large vertical height above the disk.Even the apparently bulge dominated galaxy NGC3564is well described by a thick disk component.The remaining bulge light after subtraction of the thin/thick disk combination is comparable to that of the other galaxies.This implies that all bulges of our S0galaxies could not be well de-scribed by a traditional de Vaucouleurs R1/4bulge.In ad-dition,any bulge component would be tooﬂat to account for all the light high above the disk at large galactocentric radii.Table 5.Radial and verticalﬁtting regions for the thick/thin disk components with(1)galaxy name,(2)be-ginning and end of thick/thin disk vertical region,and(3) beginning and end of thick/thin disk radial region4.1.Fitting regionsOne of the important constraints forﬁtting empirical,sur-face photometric models to observed data is the deﬁnition of the actual regions which are marked to characterise the individual model components.Therefore we list in Table 5for each galaxy the radial and vertical ranges where our thick/thin diskﬁt was applied.In all cases we restricted the twoﬁtting regions to be distinct from each other and outside the dust lane(in the case of NGC3957)or any bar/ring like feature visible in the radial proﬁle.This is obvious for theﬁrst thick disk estimation.However,in principle one could extend theﬁtting range towards the inner/outer parts for the following thick/thin disk itera-tions,since the other component in each case has already been subtracted.In addition,we masked by hand bright stars and background galaxies,forcing the program to ig-nore these regions.parison with LiteratureBurstein(1979c)only describes the‘thick disk’component qualitatively as being more diﬀuse than that of to the inner,dominating disk,and possessing aﬂattened shape. The important observation is that the scaleheight of a ﬁtted exponential to the vertical proﬁles increases with radial distance R.He determines aﬂattening,deﬁned as the intrinsic z-thickness compared to the diameter a,of z/a=0.25−0.2atµB=25.0which is somewhere between thin disks(z/a<∼0.1)and E4ellipticals(z/a=0.6)forﬁve edge-on S0galaxies.Weﬁnd values of0.29(NGC2310)or 0.32(NGC5047)comparing minor to major axis diameter at the second outermost contour(cf.Fig.B.2,B.8).While comparing scale parameter ratios in the liter-ature one has to keep in mind that they are often ob-tained with very diﬀerentﬁtting methods and even dif-ferentﬁtting functions for the vertical distribution of thin and thick disk light.As discussed in Sect.3.3this already implies systematic diﬀerences of at least20%. Surprisingly,there are no detailed parameter studies for thick disks of S0galaxies in the literature that provide。