Searches for high redshift galaxies using gravitational lensing

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High-Redshift Supernovae and the Metal-Poor Halo Stars Signatures of the First Generation o

a r X i v :a s t r o -p h /9701093v 1 15 J a n 1997High Redshift Supernovae and the Metal-Poor Halo Stars:Signatures of the First Generation of GalaxiesJordi Miralda-Escud´e 1,2,3and Martin J.Rees 1,31Institute for Advanced Study,Princeton,NJ 085402University of Pennsylvania,Dept.of Physics and Astronomy,David Rittenhouse Lab.,209S.33rd St.,Philadelphia,PA 19104(present address)3Institute of Astronomy,University of Cambridge,Cambridge CB30HA,UK ReceivedABSTRACTRecent evidence on the metal content of the high-redshift Lyαforest seen in quasar spectra suggests that an early generation of galaxies enriched the intergalactic medium(IGM)at z∼>5.We calculate the number of supernovae that need to have taken place to produce the observed metallicity.The progenitor stars of the supernovae should have emitted∼20ionizing photons for each baryon in the universe,i.e.,more than enough to ionize the IGM.We calculate that the rate of these supernovae is such that about one of them should be observable at any time per square arc minute.Theirﬂuxes are,of course, extremely faint:at z=5,the peak magnitude should be K=27with a duration of∼1year.However,these supernovae should still be the brightest objects in the universe beyond some redshift,because the earliest galaxies should form before quasars and they should have very low mass,so their luminosities should be much lower than that of a supernova.We also show that,under the assumption of a standard initial mass function, a signiﬁcant fraction of the stars in the Galactic halo should have formed in the early galaxies that reionized and enriched the IGM,and which later must have merged with our Galaxy.These stars should have a more extended radial distribution than the observed halo stars.Subject headings:Galaxy:halo-galaxies:formation-large-scale structure of universe-quasars:absorption lines-supernovae:general1.IntroductionEver since the discovery of theﬁrst high-redshift quasar(Schmidt1965),quasars have maintained their title as the objects with the highest known redshift;the present record holder is a quasar at z=4.89(Schmidt,Schneider,&Gunn1991).Nevertheless,the highest known redshifts of galaxies have followed closely behind,with bright radio galaxies having been found up to z=4.45(Lacy et al.1994;Rawlings et al.1996);more recently, galaxies with high star formation rates have been identiﬁed from interstellar absorption lines at z=2to3(Steidel et al.1996)and from the Lyαemission line at z=4.55(Hu& McMahon1996).In fact,if quasars are related to supermassive black holes that formed in the centers of high-redshift galaxies,we should expect that many galaxies already existed before theﬁrst quasars appeared.In any‘bottom-up’theory where the observed structure in the universe forms by hierarchical gravitational collapse,and the primordial densityﬂuctuations extend to suﬃciently small scales,theﬁrst galaxies to form must have had much smaller masses than the present galaxies.Theﬁrst stars should have formed in systems with velocity dispersions of∼10Km s−1or lower,corresponding to the lowest temperatures(T∼104 K)that allow cooling and dissipation of the gas by atomic processes(systems with even lower virial temperatures can cool and dissipate through molecular hydrogen,but this cooling process should be suppressed by photodissociation of the molecules after emission of a number of UV photons that is much smaller than that needed to reionize the universe; see Haiman,Rees,&Loeb1996).These systems would be very unlikely to form quasars, because even a small fraction of their baryons turning into stars should provide suﬃcient energy(via ionization,stellar winds or supernovae)to expel the remaining gas from the shallow potential well(e.g.,Couchman&Rees1986;Dekel&Silk1986).Deeper potential wells,forming at later epochs,are probably needed to form supermassive black holes ingalactic centers.Even if all the baryons were converted into stars very eﬃciently in these early dwarf galaxies,with a baryonic mass M b∼<108M⊙,their total stellar luminosity would be much smaller than in L∗galaxies at present,simply due to their small mass.Since only a small fraction of the baryons in these systems is likely to turn into stars before the gas is ejected, the total stellar mass in theﬁrst galaxies to form in the universe should be much smaller than108M⊙.This implies that a supernova in one of theseﬁrst galaxies to form will be far brighter than the galaxy itself.Thus,the brightest probes of the era when the reionization of the intergalactic medium(IGM)started should be supernovae in very small galaxies, caused by the death of the same stars responsible for theﬁrst ionizing photons.In this paper,we shall estimate the number of supernovae that should have taken place in these galaxies and should be observable at very high redshift,and their apparent magnitudes.2.Rate of High Redshift SupernovaeThe scenario where theseﬁrst small galaxies caused the reionization of the universe is strongly supported by recent evidence that the metal abundance in the Lyαforest absorption lines with N HI∼>1014cm−2is typically Z∼10−2Z⊙,from observations of CIV lines(see Tytler et al.1995,Songaila&Cowie1996and references therein).There is relatively little uncertainty in the number of UV photons that were emitted by the stars that produced a given mass of heavy elements,because the heavy elements originate from the supernovae resulting from the same stars that emit most of the ionizing photons (although the C/O ratio is more uncertain because carbon is more abundantly produced in lower mass stars).According to the most recent calculations(Madau&Shull1996 and references therein),the energy of Lyman continuum photons emitted is0.2%of the rest-mass energy of the heavy elements produced.Thus,the energy emitted in ionizingphotons per baryon is0.002m p c2¯Z=2¯Z MeV,where¯Z is the average metallicity of all baryons in the universe,so only¯Z=10−5is needed to have emitted one ionizing photon for each baryon.If¯Z=10−2Z⊙=2×10−4,then20ionizing photons must have been emitted per baryon when the heavy elements were made.Furthermore,if these were the photons responsible for reionizing the universe,then each baryon must have recombined20times on average during the reionization epoch.This is a reasonable number,because a fraction of these photons were probably absorbed in the systems where the stars were born before the gas was expelled,and those that escaped could also have been absorbed in Lyman limit systems before the universe became transparent.Thus,there is no need to invoke ejection of gas by more massive galaxies that can accrete the ionized IGM to explain a metallicity ¯Z=10−2Z⊙.We can now calculate the number of supernovae that were required for enriching the gas in the IGM to the average metallicity of Z=2×10−4that is observed in the Lyαforest at z≃3.This number should depend only on the IGM density and the supernova yields,and should be independent of any other details related to the theory for galaxy formation and the type of galaxies that ejected the enriched gas.Recent simulations of cold dark matter models show that the absorption lines in the Lyαforest can be identiﬁed with the IGM,with densityﬂuctuations caused by gravitational collapse,and that most of the baryons should be in the IGM in these models(Cen et al.1994,Hernquist et al.1996, Miralda-Escud´e et al.1996).Thus,it is reasonable to assume that the high-z supernovae enriched all the baryons in the universe to a mean at metallicity at least as high as that of the Lyαforest.Since each supernova produces an average of∼1M⊙of heavy elements(with uncertainties depending on the assumed initial mass function and supernova models; see Woosley&Weaver1995),this implies that a supernova took place at high redshiftfor each5000M⊙of baryons in the universe.We shall assume a high baryon densityΩb=0.025h−2,in agreement with the primordial deuterium abundance measured by Burles&Tytler(1996)and by Tytler,Fan,&Burles(1996).Notice that this implies that most of the baryons at the present time are dark,so many more baryons than those we observe in galaxies had to be enriched at high redshift.Assuming theΩ=1 cosmological model,the total mass of baryons in a redshift shell of width∆z around us is M b=(6c3Ωb)/(GH0)[1−(1+z)−1/2]2/(1+z)3/2∆z,where H0is the present Hubble constant.With the above rate of supernovae per baryon mass(assumed to take place within the epoch corresponding to the redshift shell∆z),and taking into account that the supernovae within the shell would be seen by us over a time interval H−10∆z/(1+z)3/2,the total supernova rate observed over all the sky isR Sup=1.8×108h−2[1−(1+z)−1/2]2yr−1.(1) or,for z∼5,about1supernova per square arc minute per year.3.Apparent MagnitudesMost of these supernovae should be Type II which,if the progenitor is a red supergiant, have a plateau of the luminosity in their lightucurves from1to80days after the explosion, with L≃3×1042erg/s(Woosley&Weaver1986).A note of caution should be made here, in that the low-metallicity progenitors of these early supernovae could be very diﬀerent from the high metallicity counterparts.As illustrated by the case of SN1987A,it is probably not possible at this stage to predict the type of supernovae we should expect from thisﬁrst generation of stars;in particular,the possibility that some supernovae might reach higher intrinsic luminosities than regular Type IIs should be kept in mind.A duration of80days would be redshifted to more than a year at redshifts z>4,where the supernovae from stars responsible for the reionization of the universe should occur.At any random timethere should therefore be one or more supernovae per square arc minute visible in the sky. Of course,many more supernovae should have occurred in more massive galaxies at later epochs(producing the metals in stars and interstellar gas at present),and possibly in small systems that ejected their gas and continued to enrich the IGM.The main diﬃculty in detecting these supernovae is obviously the extremely faintﬂux expected.Supernovae should be the brightest objects in the universe at very high redshift,but they are of course much fainter than quasars and,as the redshift increases,the bolometricﬂuxes decrease at least as rapidly as(1+z)2.One should point out,however, that when observing at aﬁxed,long wavelenth such that the supernovae are observed on the Rayleigh-Jeans part of the spectrum,theﬂux actually becomes brighter as1+z,in the limit of high redshift.To estimate the apparent magnitudes of the supernovae,we assume a blackbody spectrum,which is a suﬃciently close approximation for our purpose.In Figure1we show the apparent magnitudes in several bands for a luminosity L=3×1042erg/s,and temperatures T=25000K and T=7000K.The high temperature is reached∼1day after the explosion,when the luminosity drops to the value in the plateau part of the lightcurve;during the next few days the temperature cools,reaching a value near7000K after about a week,and then it stays constant until the luminosity starts decreasing. Immediately after the explosion,when the shock reaches the surface of the star,the luminosity and temperature can be much higher and the apparentﬂux can be brighter by a factor∼10relative to the values in Fig.1,but this phase only lasts for∼1hour.The apparent magnitudes have been calculated for theΩ=1model with H0=70Km/s/Mpc, from theﬂux at the central wavelengths of the bands,using the central wavelengths and zero-magnitudeﬂuxes given in Allen(1973).The high-redshift cutoﬀin the curves in Figure 1indicate the redshift where the supernova light would be absorbed by the Lyαforest.At high redshift,the supernovae must obviously be searched in the infrared.The faintest galaxy surveys from the ground have reached magnitudes K≃25(Cowie et al.1994).From Fig.1,type II supernovae would have similar magnitudes at z≃2.5, although searching for variable objects should require more telescope time than simple object identiﬁcation.In order toﬁnd supernovae at redshifts higher than known quasars, fainterﬂuxes by a factor of5−10need to be detected.This might be achieved with implementation of adaptive optics on large ground-based telescopes;in the longer term,the New Generation Space Telescope should certainly be capable to observe these supernovae (see Mather&Stockman1996).We emphasize again the large uncertainty in predicting the types and absolute magnitude of supernovae from these early generation of stars.One possibility to detect these supernovae before more powerful telescopes and cameras in the infrared can be built is to use the magnifying power of gravitational lensing in galaxy clusters.The deﬂection angles of the most massive clusters of galaxies are as large as b∼30′′,with critical lines of total length of several arc minutes.The cross section for magnifying a source by more than a factor A is∼πb2/A2,or0.01square arc minutes for A=10.Thus,any rich lensing cluster should have a1%chance of having a high-redshift supernova magniﬁed by a factor larger than10at any time.The highly magniﬁed images would always appear in pairs around critical lines,and would be simple to identify only from their positions and colors given a lensing model of the cluster(see Miralda-Escud´e& Fort1993).Later,variability would have to be detected to distinguish the supernova from a faint,compact galaxy.4.The Present Distribution of Population III StarsWe have suggested in this paper that,under reasonable assumptions,supernovae should be the brightest objects in the universe beyond some redshift,in particular during theearly phases of the reionization.The supernovae might therefore be theﬁrst observational evidence we shall have of this epoch,when the very faint apparent magnitudes expected are observable.The other observable signature of this epoch may be the21cm absorption or emission by the neutral intergalactic gas(Scott&Rees1994;Madau,Meiksin&Rees 1996).The UV and heavy elements abundance inferred from quasar absorption lines allow us, as we have seen,to draw quantitative conclusions about the minimum number of high-mass stars formed beyond z=5:to produce a metallicity Z=2×10−4requires one supernova for each∼5000M⊙of baryons.This inference is quite robust,being insensitive to the details of structure and galaxy formation at high redshift,which of course depend on the cosmological assumptions.However,the total mass of stars formed depends on the IMF,and is therefore much more uncertain.For a standard IMF,∼100M⊙of stars need to be formed to produce one supernova,so2%of the baryons should have been turned into stars by the time the IGM reached this level of enrichment.Notice that this is equivalent to20%of the observed baryons in galaxies today,given our adopted value ofΩb which implies that only∼10%of the baryons are in known stars and gas in galaxies.It is of course quite possible that the IMF was diﬀerent for these early stars,given the diﬀerent physical environment(a higher ambient temperature,absence of heavy elements to act as coolants and provide opacity, and no signiﬁcant magneticﬁelds).Direct clues to the slope of the high-mass IMF may come from(for instance)the relative ionization levels of H and He and heavy elements, which depend on the background radiation spectrum shortward of the Lyman limit,or from relative abundances of heavy elements relative to carbon.Conceivably,all the early stars might be of high-mass,so that no coeval low-mass stars survive;at the other extreme,the early IMF could have been much steeper than the standard one,in which case there could be many pregalactic brown dwarfs.Would any of these“Population III”stars be observable today?Let us consider the observational consequences of the simplest assumption:that the early IMF was the same as in the solar neighborhood.In that case,most of the present luminosity from the Population III would arise from red giants and stars at the tip of the main-sequence,with M∼0.8M⊙. Where should these stars be today?After theﬁrst galaxies ejected all their gas back to the IGM,the stars that had been formed should have remained in orbit near the center of the dark matter halos.The stars then behave as collisionless matter as the halos merge with larger objects,until the present galaxies are formed.We would therefore expect that these stars would at present be distributed approximately like the dark matter in galactic and cluster halos,and in addition there should be some surviving galaxies from that epoch which have not merged into much larger objects(or have survived in orbit after merging with a large halo,having escaped tidal disruption)and still have the Population III stars in their centers.The halos of stars formed in this way around galaxies might be somewhat more centrally concentrated than the dark matter,if many mergers take place with only a moderate increase of the halo mass at each merger(so that dynamical friction is eﬀective after each merger and it can bring the stars near the center of the newly formed halo before tidal disruption occurs).In fact, particles that start near the centers of halos that merge tend to end up near the center of the merger product(e.g.,Spergel&Hernquist1992).The known halo stars have a very steep density proﬁle,ρ∝r−3.5,and their total mass is M∼109M⊙(e.g.,Morrison1993).This mass is comparable to the total mass we would expect in the halo in the Population III stars,if the total mass of the halo of our Galaxy is5×1011M⊙,with a baryon fraction of10%,and if2%of the baryons formed Population III stars.Therefore,if the stellar mass function in theﬁrst galaxies was normal,a sizable fraction of the halo stars should have originated there(this is not surprising,because it isderived from the assumption that the halo stars created their own metal abundance).It seems diﬃcult that the process of dynamical friction alluded to above can result in the steep slope of the halo stars.However,the halo density proﬁle might become shallower at large radius(see Hawkins1983and Norris&Hawkins1991for current observational evidence on this possibility),and a second halo population in the outer part of the galaxy(R∼100 Kpc)might be the remnant of the Population III.These halo stars could be found in the Hubble Deep Field(HDF,Williams et al.1996).If the stellar mass of this outer halo is 109M⊙,there should be∼108stars near the main-sequence turnoﬀ,i.e.,we expect a few stars in the HDF(with area4.4arcmin2);these would have colors I−V≃1.5,I∼25at distances of100Kpc.From Fig.2in Flynn,Gould,&Bahcall,we see that there is at least one stellar object with these characteristics in the HDF.Several other observations may help to test the existence of the Population III stars. An outer stellar halo would also imply a certain number of high-velocity stars near the solar neighborhood.A stellar population may be found in the halos of external galaxies,with density proﬁles similar to the dark matter.Sackett et al.(1994)found a luminous haloin the galaxy NGC5907with M/L=500(i.e.,about ten times more light than what we expect for the Population III).Planetary nebulae could also be found in nearby halos of galaxies or galaxy groups;several of them were reported recently by by Theuns&Warren 1996)in the Fornax cluster.There is also the possibility that the IMF in the early galaxies produced a large number of brown dwarfs.In this case,a large fraction of the baryons could have been turned into brown dwarfs,and these could be detected in ongoing microlensing experiments towards the LMC(see Paczy´n ski1996).If the baryon fraction in the universe is10%,the optical depth of these brown dwarfs toward the LMC could be as high as a few times10−8.Finally,we notice that the metallicity distribution of the Population III stars is diﬃcultto predict.If only a small fraction of the neutral IGM collapsed to galaxies before the reionization,then the gas in these galaxies could reached high metallicities and formed stars, and the metallicity could have diluted in the IGM when the gas was ejected.At the same time,the metal abundance of the IGM after reionization could be highly inhomogeneous, so some galaxies formed later could have very low metallicities.Therefore,it is diﬃcult to predict even if the average metal abundance of the Population III stars should be higher, lower or similar to the more centrally concentrated halo stars,let alone the distribution of these metallicities.5.ConclusionsAs the observational techniques improve our ability to detect extremely faint sources, and higher redshift objects can be searched for to continue unravelling the history of galaxy formation,supernovae should become the brightest observable sources.These supernovae created the heavy elements that were expelled to the IGM,and their progenitor stars are the most likely sources of the photons that reionized the universe.The expected rates of these supernovae,calculating under the assumption of a high baryon density(Ωb h2=0.025), and an average metal production of¯Z=10−2Z⊙,is as high as1supernova per square arc minute per year.To detect the supernovae,theﬂux limits of the faintest sources detectable with our telescopes will probably need to be pushed by another∼2magnitudes,although theﬁrst examples might be discovered at brighterﬂuxes behind clusters of galaxies,using the lensing magniﬁcation.Any low-mass stars that were formed in theﬁrst small galaxies where these supernovae took place should be observable today.We have argued that,if the IMF in these galaxies was similar to the present one in our galactic disk,the Population III stars are likely to account for a large fraction of the stars in our galactic halo,although most of them shouldbe in an as yet undetected outer halo with a shallower density proﬁle than the known,inner stellar halo.We thank Len Cowie,Andy Gould and John Norris for stimulating discussions.JM acknowledges support by the W.M.Keck Foundation at IAS.REFERENCESAllen,C.W.1973,Astrophysical Quantities(London:Athlone Press)Burles,S.,&Tytler,S.1996,submitted to Science(astroph9603069)Cen,R.,Miralda-Escud´e,J.,Ostriker,J.P.,&Rauch,M.1994,ApJ,437,L9 Couchman,H.M.P.,&Rees,M.J.,1986,MNRAS,221,53Cowie,L.L.,Gardner,J.P.,Hu,E.M.,Songaila,A.,Hodapp,K.-W.,& Wainscoat,R.J.1994,ApJ,434,114Dekel,A.,&Silk,J.1986,ApJ,303,39Flynn,C.,Gould,A.,&Bahcall,J.N.1996,ApJ,466,L55Haiman,Z.,Rees,M.J.,&Loeb,A.1996,ApJ,submitted(astroph-9608130) Hawkins,M.S.1983,MNRAS,206,433Hernquist,L.,Katz,N.,Weinberg,D.H.,&Miralda-Escud´e,J.1996,ApJ,457,L51 Hu,E.M.,&McMahon,R.G.1996,Nature,382,231Lacy,M.,et al.1994,MNRAS,271,504Madau,P.,Meiksin,A.,&Rees,M.J.1996,ApJ,submitted(astroph9608010) Madau,P.,&Shull,J.M.1996,ApJ,457,551Mather,J.,&Stockman,H.1996,NASA Report.Miralda-Escud´e,J.,&Fort,B.1993,ApJ,417,5Miralda-Escud´e,J.,Cen,R.,Ostriker,J.P.,&Rauch,M.1996,ApJ,471,582Morrison,H.L.1993,AJ,106,578Norris,J.,&Hawkins,M.S.1991,ApJ,380,104Paczy´n ski,B.1996,ARA&A,34,XXXRawlings,S.,Lacy,M.,Blundell,K.M.,Eales,S.A.,Bunker,A.J.,&Garrington,S.T.1996,Nature,383,502Sackett,P.D.,Morrison,H.L.,Harding,P.,&Boroson,T.A.1994,Nature,370,441Schmidt,M.1965,ApJ,141,1295Schneider,D.P.,Schmidt,M.,&Gunn,J.E.1991,AJ,101,2004Scott,D.,&Rees,M.J.1990,MNRAS,247,510Songaila,A.,&Cowie,L.L.1996,AJ,in press(astro-ph9605102)Spergel,D.N.,&Hernquist,L.1992,ApJ,397,L75Steidel,C.C.,Giavalisco,M.,Pettini,M.,Dickinson,M.,&Adelberger,K.L.1996,ApJ, 462,L17Theuns,T.,&Warren,S.J.1996,submitted to MNRAS(astro-ph9609076)Tytler,D.,Fan,X.-M.,Burles,S.,Cottrell,L.,Davis,C.,Kirkman,D.,&Zuo,L.1995,in QSO Absorption Lines,ed.G.Meylan,p.289Tytler,D.,Fan,X.-M.,&Burles,S.1996,Nature,381,207Williams,R.,et al.1996,Science with the Hubble Space Telescope II,eds.P.Benvenuti,F.D.Macchetto,&E.J.Schreier(Baltimore:STScI),in pressWoosley,S.E.,&Weaver,T.A.1995,ApJS,101,181Woosley,S.E.,&Weaver,T.A.1986,ARA&A,24,205Fig.1.—Apparent magnitude of a supernova as a function of redshift in diﬀerent bands,as labeled in theﬁgure,for two diﬀerent temperatures.We assume the supernova spectrum is a blackbody with the luminosity and temperature indicated.Supernovae Type II generally have a plateau of constant luminosity in their lightcurves with the value assumed in thisﬁgure lasting for80days.A temperature of25000K is reached∼two days after the explosion, and a week later the temperature has dropped to near7000K,where it stays constant for the next two months.。

thehitchhikersguidetothegalaxy银河系漫游指南

Searching for the answers to life, the universe, and everything? Well look no further…The Hitchhikers Guide to the GalaxyBy Douglas AdamsPublished by Serious Productions© 1976A Sci-fi thrillerPage Count: 216Your Guide to SurvivalBy ATPlanning on taking a quick stop by Ursa Minor? Just don’t forget the number one rule of thumb when traveling across the galaxy: Always bring a blanket. Tips like these are shared periodically throughout The Hitchhiker’s Guide to the Galaxy, by Douglas Adams. In it, the deepest questions of the universe will at last be answered. The protagonist, Arthur Dent, is the sole survivor of planet Earth since it was destroyed for the means of making an intergalactic highway. Dent finds himself aboard a spaceship with Ford Prefect, his quirky best friend. Together they make their way across the galaxy through a series of highly improbable coincidences: stumbling upon the president of the galaxy, surviving in the vacuum of space, and finding the legendary planet of Magrathea. The novel’s plot revolves around what happens to this unlikely crew as they are the first beings in five million years to reach Magrathea. This concept of life outside of Earth and traveling through great distances of space is what will likely keep the reader reading.In the beginning this world renowned book pulls readers in through Adams unique tone including multiple hilarious scenes that will leave one laughing out loud. The book is comprised of twenty-two chapters, each short in length making the book a quick and easy read. It also has many elements that many teenagers enjoy including humor while maintaining a thought-provoking plot line.The strong suit of The Hitchhiker’s Guide to the Galaxy is definitely its extensive creativity. Within the book there is another book entitled The Hitchhiker’s Guide to the Galaxy, where one will find descriptions of creatures and places throughout the galaxy. Some of its excerpts being literally out of this world! Who could have thought of its description of the Babble Fish: “it feeds on brainwave energy received not from its carrier but from those around it. It absorbs all unconscious mental frequencies from this brainwave energy to nourish itself.” These overly complex ideas put a comic spin on the plot which is another strength. However straying from the plot to explain something can often make readers confused. This drift from the plot resulted in a very disorganized composite of certain scenes in the book. Adams may have chose to include this skipping around to lighten up the more serious parts of the book and remind the reader that it is a comic novel. In other words those looking for an uplifting and humorous book about life’s greatest mysteries will surely find The Hitchhiker’s Guide to the Galaxy very entertaining. After reading this, one can not help but ponder the very insignificance that our whole planet really has.Douglas Adams’ other books exhibit his passion for science fiction, specifically the larger world that exists outside of Earth. The Hitchhiker’s Guide to the Galaxy was adapted into a mini TV series, and a full length feature film, in 2005. Adams has a series of follow up books entitled The Restaurant at the End of the Universe, Life the Universe and Everything, So Long, and Thanks for all the Fish, and many others. These novels include many jokes originating from The Hitchhikers Guide to the Galaxy. Adams’ career of wild success spun off of this one ground breaking novel, a truly remarkable feat.Unfortunately his career came to an abrupt end when he died at the age of forty-nine in2001. His legacy lives on through this, and many other captivating books that will leave one wondering whether or not we are indeed alone in the universe.Below is given annual work summary, do not need friends can download after editor deleted Welcome to visit againXXXX annual work summaryDear every leader, colleagues:Look back end of XXXX, XXXX years of work, have the joy of success in your work, have a collaboration with colleagues, working hard, also have disappointed when encountered difficulties and setbacks. Imperceptible in tense and orderly to be over a year, a year, under the loving care and guidance of the leadership of the company, under the support and help of colleagues, through their own efforts, various aspects have made certain progress, better to complete the job. For better work, sum up experience and lessons, will now work a brief summary.To continuously strengthen learning, improve their comprehensive quality. 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Over the past year, through continuous learning and fumble, studied the gas generation, collection and methods, gradually familiar with and master the company introduced the working principle, operation method of gas machine. With the help of the department leaders and colleagues, familiar with and master the launch of the division principle, debugging method of the control system, and to wuhan Chen Guchong garbage power plant of gas machine control system transformation, learn to debug, accumulated some experience. All in all, over the past year, did some work, have also made some achievements, but the results can only represent the past, there are some problems to work, can't meet the higher requirements. In the future work, I must develop the oneself advantage, lack of correct, foster strengths and circumvent weaknesses, for greater achievements. Looking forward to XXXX years of work, I'll be more efforts, constant progress in their jobs, make greater achievements. 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The Extremely Red Objects Found Thus Far in the Caltech Faint Galaxy Redshift Survey

a rXiv:as tr o-ph/988343v13Aug1998The Extremely Red Objects Found Thus Far in the Caltech Faint Galaxy Redshift Survey 1Judith G.Cohen 2,David W.Hogg 3,4,5Roger Blandford 3,Michael A.Pahre 2,5,6&Patrick L.Shopbell 2ABSTRACT We discuss the very red objects found in the ﬁrst ﬁeld of the Caltech Faint Galaxy Redshift Survey,for which the observations and analysis are now complete.In this ﬁeld,which is 15arcmin 2and at J005325+1234there are 195objects with K s <20mag,of which 84%have redshifts.The sample includes 24spectroscopically conﬁrmed Galactic stars,136galaxies,three AGNs,and 32objects without redshifts.About 10%of the sample has (R −K )≥5mag.Four of these objects have redshifts,with 0.78≤z ≤1.23.Three of these are based on absorption features in the mid-UV,while the lowest redshift object shows the standard features near 4000˚A .Many of the objects still without redshifts have been observed spectroscopically,and no emission lines were seen in their spectra.We believe they are galaxies with z ∼1−1.5that are red due to their age and stellar content and not to some large amount of internal reddening from dust.Among the many other results from this survey of interest here is a determination of the median extinction in the mid-UV for objects with strong emission line spectra at z ∼1−1.3.The result is extinction by a factor of ∼2at 2400˚A .1.Introduction We have completed the analysis of the data for the ﬁrst ﬁeld of this survey,which is 2x 7.3arcmin 2ﬁeld at J005325+1234.The sample is selected ignoring morphology at K and consists of the 195objects with K <20mag in this ﬁeld.These were observed with the LowResolution Imaging Spectrograph(Oke et al.1995)at the Keck Observatory.Six color photometry (UBV RIK)is available for the entireﬁeld as well from Pahre et al.(1998).Redshifts were successfully obtained for163of the195objects in the sample to achievea completeness of84%.These redshifts lie in the range[0.173,1.44]and have a median of0.58(excluding24spectroscopically conﬁrmed Galactic stars).The sample includes two broad lined AGNs and one QSO.The objects are assigned to spectral classes based on the relative preponderance of emission lines versus absorption lines in their spectra.The four spectral classes used for extragalactic objects are“E”for emission line dominated spectra(33galaxies),“A”for absorption line dominated spectra(51galaxies),“C”for composite spectra(52galaxies),and“Q”for AGNs.A few starbursts were found,classiﬁed as“B”,but for the present discussion they are grouped together with the emission line galaxies.2.Rest Frame Spectral Energy DistributionsThe galaxy rest frame SEDs derived from out UBV RIK photometry are very closely correlated to the galaxy spectral types.Both are also correlated with galaxy luminosity;blue galaxies show the signature of recent star formation in their spectra and are less luminous forz<0.8than red galaxies which show no evidence for recent star formation in their spectra. Representative SEDs are shown in Figure1.The SEDs for selected galaxies(D0K183,172,108, 188and158)with z>0.9shown in Figure1a are remarkablyﬂat(blue).Figure1b shows the SEDs for all the absorption line galaxies in the z=0.58peak;they have quite steep(red)spectra.2.1.The Extremely Red Objects in Our SampleThere are24Galactic stars in this sample,mostly M dwarfs or M subdwarfs.The reddest galactic star identiﬁed spectroscopically in thisﬁeld has(R−K)=4.6mag.There are19objects in this sample with(R−K)≥5mag,which we call the very red objects,and which we believe to be galaxies rather than Galactic stars.Four of these have redshifts,most of which are somewhat uncertain.Figure2shows the rest frame SEDs for the four very red galaxies with redshifts.The second panel of Figure2shows the SEDs for three of the very red objects which do not have redshifts,calculated assuming z=1.Redder than B,these look similar to those SEDs shown in theﬁrst panel of thisﬁgure,but the objects are somewhat fainter.Most of the U and B magnitudes for these objects are upper limits,as indicated by the vertical bars going downward from the relevant points.A more complete discussion of the redshift peaks(i.e.groups and poor clusters of galaxies), luminosity function,the cosmological volume density,the constraints on mergers,the ultraviolet extinction and other issues can be found in two papers,one of which has been submitted to ApJFig.1.—The rest frame spectral energy distributions(SEDs)for selected galaxies.The abscissa is the rest frequency and the rest wavelengths corresponding to our6color photometry augmented by the two supplementary ultraviolet bands P and Q(log(ν)=15.0and15.1)are indicated.The ordinate is the logarithm of the spectral power in units of both L∗B and W.Each galaxy SED shows the rest wavelengths corresponding to the observations and dashed lines are used to indicate extrapolations.The upper horizontal scale can be used in conjunction with the K point to measure the redshift of the galaxy.Fig. 2.—The rest frame SEDs for the four extremely red galaxies for which redshifts have been determined from our survey.The second panel shows the rest frame SEDs for three of the extremely red galaxies without redshifts,calculated assuming z=1.The line in the lower left indicates how the SEDs will shift for0.5<z<1.5.(Cohen et al.1998a)while the other(Cohen et al.1998b)will be published in ApJS.3.Final CommentsWe have determined the fraction of very red objects among our sample.For counts to K<20 mag,∼10%of the sample of195objects is very red,i.e.has(R−K)≥5mag.If one excludes the known Galactic stars from the sample,this fraction does not change substantially.We have examined the spectra of many of these extremely red objects and have succeeded in determining the redshifts of four of them,although the redshifts are not as certain as one might desire.We suggest that these are galaxies with z∼1−1.5in which reddening by dust is not playing a major role.In particular they are not heavily reddened starbursts.(If they were,we should have seen some moderately reddened emission line galaxies,and there were no such beasts among our sample).Instead we believe their extremely red colors are a direct consequence of their age,stellar composition,k-corrections,etc.and that these extremely red objects are the analogs at this redshift range of local elliptical galaxies.We thus support Persson et al.(1993)and Graham&Dey(1996),who among others,have speculated that such objects are passively-evolved elliptical galaxies with z>1.More work is going to be required to get someﬁrst class redshifts for these,or similar, hopefully brighter,objects,to establish their nature in a more deﬁnitive way.The entire Keck/LRIS user community owes a huge debt to Jerry Nelson,Gerry Smith,Bev Oke,and many other people who have worked to make the Keck Telescope and LRIS a reality. We are grateful to the W.M.Keck Foundation,and particularly its late president,Howard Keck, for the vision to fund the construction of the W.M.Keck Observatory.JGC is grateful for partial support from STScI/NASA grant AR-06337.12-94A.DWH and MAP were supported in part by Hubble Fellowship grants HF-01093.01-97A and HF-01099.01-97A from STScI(which is operated by AURA under NASA contract NAS5-26555).REFERENCESCohen,J.G.,Hogg,D.W.,Pahre,M.A.,Blandford,R.,Shopbell,P.L.&Richberg,K.,1998, ApJS,submittedCohen,J.G.,Blandford,R.,Hogg,D.W.,Pahre,M.A.&Shopbell,P.L.,1998,ApJ,submitted Graham,J.R.,&Dey,A.1996,ApJ,471,720Oke,J.B.,Cohen,J.G.,Carr,M.,Cromer,J.,Dingizian,A.,Harris,F.H.,Labrecque,S., Lucinio,R.,Schaal,W.,Epps,H.,&Miller,J.1995,PASP,107,307Pahre,M.A.,et al.1998,ApJS,submittedPersson,S.E.,McCarthy,P.J.,Dressler,A.,&Matthews,K.,1993,in The Evolution of Galaxies and their Environments,eds.D.Hollenbach,H.Thronson&J.M.Shull,NASA Conference Publication3190,69。

斑马技术公司DS8108数字扫描仪产品参考指南说明书

Chapter 1: Getting Started Introduction .................................................................................................................................... 1-1 Interfaces ....................................................................................................................................... 1-2 Unpacking ...................................................................................................................................... 1-2 Setting Up the Digital Scanner ....................................................................................................... 1-3 Installing the Interface Cable .................................................................................................... 1-3 Removing the Interface Cable .................................................................................................. 1-4 Connecting Power (if required) ................................................................................................ 1-4 Configuring the Digital Scanner ............................................................................................... 1-4

Royal Greenwich Observatory

Abstract.
2 supernovae can provide a distance indicator and \standard clock" to study the cosmological parameters q0 , , 0, and H0 . This presentation and the following presentations of Kim et al. (1996), Goldhaber et al. (1996), and Pain et al. (1996) will discuss observation strategies and rates, analysis and calibration issues, the sources of measurement uncertainty, and the cosmological implications, including bounds on q0 , of these rst high-redshift supernovae from our ongoing search.
then apply for the telescope time to study them, beginning at least a few days before maximum light. To solve these problems, we developed a new search technique. Figure 1 presents a schematic outline of the strategy. Just after a new moon, we observe many tens of high-galactic-latitude elds (including known highredshift clusters when possible) on a 2.5- to 4-meter telescope. With a wide- eld camera, each image contains hundreds of galaxies at redshifts 0.3 { 0.6. Just before the following new moon, we observe the same elds again. We compare the images, thus checking tens of thousands of high redshift galaxies (including those below our detection limit) to nd the ten or so showing the new light of a supernova that was not there on the previous observation. The supernovae generally do not have time to reach maximum light, with only 2.5 to 3 weeks (or approximately 11 to 14 days in the supernova rest frame) between our after- and before-new-

The evolution of clustering and bias in the galaxy distribution

a rXiv:as tr o-ph/98528v115May1998The evolution of clustering and bias in the galaxy distribution B y J.A.Peacock Institute for Astronomy,Royal Observatory,Edinburgh EH93HJ,UK This paper reviews the measurements of galaxy correlations at high redshifts,and discusses how these may be understood in models of hierarchical gravita-tional collapse.The clustering of galaxies at redshift one is much weaker than at present,and this is consistent with the rate of growth of structure expected in an open universe.If Ω=1,this observation would imply that bias increases at high redshift,in conﬂict with observed M/L values for known high-z clusters.At redshift 3,the population of Lyman-limit galaxies displays clustering which is of similar amplitude to that seen today.This is most naturally understood if the Lyman-limit population is a set of rare recently-formed objects.Knowing both the clustering and the abundance of these objects,it is possible to deduce em-pirically the ﬂuctuation spectrum required on scales which cannot be measured today owing to gravitational nonlinearities.Of existing physical models for the ﬂuctuation spectrum,the results are most closely matched by a low-density spa-tially ﬂat universe.This conclusion is reinforced by an empirical analysis of CMB anisotropies,in which the present-day ﬂuctuation spectrum is forced to have the observed form.Open models are strongly disfavoured,leaving ΛCDM as the most successful simple model for structure formation.2J.A.Peacockcommon parameterization for the correlation function in comoving coordinates:ξ(r,z)=[r/r0]−γ(1+z)−(3−γ+ǫ),(1.2) whereǫ=0is stable clustering;ǫ=γ−3is constant comoving clustering;ǫ=γ−1isΩ=1linear-theory evolution.Although this equation is frequently encountered,it is probably not appli-cable to the real world,because most data inhabit the intermediate regime of 1<∼ξ<∼100.Peacock(1997)showed that the expected evolution in this quasilin-ear regime is signiﬁcantly more rapid:up toǫ≃3.(b)General aspects of biasOf course,there are good reasons to expect that the galaxy distribution will not follow that of the dark matter.The main empirical argument in this direction comes from the masses of rich clusters of galaxies.It has long been known that attempts to‘weigh’the universe by multiplying the overall luminosity density by cluster M/L ratios give apparent density parameters in the rangeΩ≃0.2to0.3 (e.g.Carlberg et al.1996).An alternative argument is to use the abundance of rich clusters of galaxies in order to infer the rms fractional density contrast in spheres of radius8h−1Mpc. This calculation has been carried out several diﬀerent ways,with general agree-ment on aﬁgure close to(1.3)σ8≃0.57Ω−0.56m(White,Efstathiou&Frenk1993;Eke,Cole&Frenk1996;Viana&Liddle1996). The observed apparent value ofσ8in,for example,APM galaxies(Maddox,Efs-tathiou&Sutherland1996)is about0.95(ignoring nonlinear corrections,which are small in practice,although this is not obvious in advance).This says that Ω=1needs substantial positive bias,but thatΩ<∼0.4needs anti bias.Although this cluster normalization argument depends on the assumption that the density ﬁeld obeys Gaussian statistics,the result is in reasonable agreement with what is inferred from cluster M/L ratios.What eﬀect does bias have on common statistical measures of clustering such as correlation functions?We could be perverse and assume that the mass and lightﬁelds are completely unrelated.If however we are prepared to make the more sensible assumption that the light density is a nonlinear but local function of the mass density,then there is a very nice result due to Coles(1993):the bias is a monotonic function of scale.Explicitly,if scale-dependent bias is deﬁned asb(r)≡[ξgalaxy(r)/ξmass(r)]1/2,(1.4) then b(r)varies monotonically with scale under rather general assumptions about the densityﬁeld.Furthermore,at large r,the bias will tend to a constant value which is the linear response of the galaxy-formation process.There is certainly empirical evidence that bias in the real universe does work this way.Consider Fig.1,taken from Peacock(1997).This compares dimen-sionless power spectra(∆2(k)=dσ2/d ln k)for IRAS and APM galaxies.The comparison is made in real space,so as to avoid distortions due to peculiar veloc-ities.For IRAS galaxies,the real-space power was obtained from the the projectedThe evolution of galaxy clustering and bias3Figure1.The real-space power spectra of optically-selected APM galaxies(solid circles)and IRAS galaxies(open circles),taken from Peacock(1997).IRAS galaxies show weaker clustering, consistent with their suppression in high-density regions relative to optical galaxies.The relative bias is a monotonic but slowly-varying function of scale.correlation function:Ξ(r)= ∞−∞ξ[(r2+x2)1/2]dx.(1.5)Saunders,Rowan-Robinson&Lawrence(1992)describe how this statistic can be converted to other measures of real-space correlation.For the APM galaxies, Baugh&Efstathiou(1993;1994)deprojected Limber’s equation for the angular correlation function w(θ)(discussed below).These diﬀerent methods yield rather similar power spectra,with a relative bias that is perhaps only about1.2on large scale,increasing to about1.5on small scales.The power-law portion for k>∼0.2h Mpc−1is the clear signature of nonlinear gravitational evolution,and the slow scale-dependence of bias gives encouragement that the galaxy correlations give a good measure of the shape of the underlying massﬂuctuation spectrum.2.Observations of high-redshift clustering(a)Clustering at redshift1At z=0,there is a degeneracy betweenΩand the true normalization of the spectrum.Since the evolution of clustering with redshift depends onΩ,studies at higher redshifts should be capable of breaking this degeneracy.This can be done without using a complete faint redshift survey,by using the angular clustering of aﬂux-limited survey.If the form of the redshift distribution is known,the projection eﬀects can be disentangled in order to estimate the3D clustering at the average redshift of the sample.For small angles,and where the redshift shell being studied is thicker than the scale of any clustering,the spatial and angular4J.A.Peacockcorrelation functions are related by Limber’s equation(e.g.Peebles1980): w(θ)= ∞0y4φ2(y)C(y)dy ∞−∞ξ([x2+y2θ2]1/2,z)dx,(2.1)where y is dimensionless comoving distance(transverse part of the FRW metric is[R(t)y dθ]2),and C(y)=[1−ky2]−1/2;the selection function for radius y is normalized so that y2φ(y)C(y)dy=1.Less well known,but simpler,is the Fourier analogue of this relation:π∆2θ(K)=The evolution of galaxy clustering and bias5 ever,the M/L argument is more powerful since only a single cluster is required, and a complete survey is not necessary.Two particularly good candidates at z≃0.8are described by Clowe et al.(1998);these are clusters where signiﬁcant weak gravitational-lensing distortions are seen,allowing a robust determination of the total cluster mass.The mean V-band M/L in these clusters is230Solar units,which is close to typical values in z=0clusters.However,the comoving V-band luminosity density of the universe is higher at early times than at present by about a factor(1+z)2.5(Lilly et al.1996),so this is equivalent to M/L≃1000, implying an apparent‘Ω’of close to unity.In summary,the known degree of bias today coupled with the moderate evolution in correlation function back to z=1 implies that,forΩ=1,the galaxy distribution at this time would have to consist very nearly of a‘painted-on’pattern that is not accompanied by signiﬁcant mass ﬂuctuations.Such a picture cannot be reconciled with the healthy M/L ratios that are observed in real clusters at these redshifts,and this seems to be a strong argument that we do not live in an Einstein-de Sitter universe.(b)Clustering of Lyman-limit galaxies at redshift3The most exciting recent development in observational studies of galaxy clus-tering is the detection by Steidel et al.(1997)of strong clustering in the popula-tion of Lyman-limit galaxies at z≃3.The evidence takes the form of a redshift histogram binned at∆z=0.04resolution over aﬁeld8.7′×17.6′in extent.For Ω=1and z=3,this probes the densityﬁeld using a cell with dimensionscell=15.4×7.6×15.0[h−1Mpc]3.(2.3) Conveniently,this has a volume equivalent to a sphere of radius7.5h−1Mpc,so it is easy to measure the bias directly by reference to the known value ofσ8.Since the degree of bias is large,redshift-space distortions from coherent infall are small; the cell is also large enough that the distortions of small-scale random velocities at the few hundred km s−1level are also ing the model of equation (11)of Peacock(1997)for the anisotropic redshift-space power spectrum and integrating over the exact anisotropic window function,the above simple volume argument is found to be accurate to a few per cent for reasonable power spectra:σcell≃b(z=3)σ7.5(z=3),(2.4) deﬁning the bias factor at this scale.The results of section1(see also Mo& White1996)suggest that the scale-dependence of bias should be weak.In order to estimateσcell,simulations of synthetic redshift histograms were made,using the method of Poisson-sampled lognormal realizations described by Broadhurst,Taylor&Peacock(1995):using aχ2statistic to quantify the nonuni-formity of the redshift histogram,it appears thatσcell≃0.9is required in order for theﬁeld of Steidel et al.(1997)to be typical.It is then straightforward to ob-tain the bias parameter since,for a present-day correlation functionξ(r)∝r−1.8,σ7.5(z=3)=σ8×[8/7.5]1.8/2×1/4≃0.146,(2.5) implyingb(z=3|Ω=1)≃0.9/0.146≃6.2.(2.6) Steidel et al.(1997)use a rather diﬀerent analysis which concentrates on the highest peak alone,and obtain a minimum bias of6,with a preferred value of8.6J.A.PeacockThey use the Eke et al.(1996)value ofσ8=0.52,which is on the low side of the published range of ingσ8=0.55would lower their preferred b to 7.6.Note that,with both these methods,it is much easier to rule out a low value of b than a high one;given a singleﬁeld,it is possible that a relatively‘quiet’region of space has been sampled,and that much larger spikes remain to be found elsewhere.A more detailed analysis of several furtherﬁelds by Adelberger et al. (1998)in fact yields a biasﬁgure very close to that given above,so theﬁrstﬁeld was apparently not unrepresentative.Having arrived at aﬁgure for bias ifΩ=1,it is easy to translate to other models,sinceσcell is observed,independent of cosmology.For lowΩmodels, the cell volume will increase by a factor[S2k(r)dr]/[S2k(r1)dr1];comparing with present-dayﬂuctuations on this larger scale will tend to increase the bias.How-ever,for lowΩ,two other eﬀects increase the predicted densityﬂuctuation at z=3:the cluster constraint increases the present-dayﬂuctuation by a factor Ω−0.56,and the growth between redshift3and the present will be less than a factor of4.Applying these corrections givesb(z=3|Ω=0.3)The evolution of galaxy clustering and bias7 87GB survey(Loan,Lahav&Wall1997),but these were of only bare signiﬁcance (although,in retrospect,the level of clustering in87GB is consistent with the FIRST measurement).Discussion of the87GB and FIRST results in terms of Limber’s equation has tended to focus on values ofǫin the region of0.Cress et al.(1996)concluded that the w(θ)results were consistent with the PN91 value of r0≃10h−1Mpc(although they were not very speciﬁc aboutǫ).Loan et al.(1997)measured w(1◦)≃0.005for a5-GHz limit of50mJy,and inferred r0≃12h−1Mpc forǫ=0,falling to r0≃9h−1Mpc forǫ=−1.The reason for this strong degeneracy between r0andǫis that r0parame-terizes the z=0clustering,whereas the observations refer to a typical redshift of around unity.This means that r0(z=1)can be inferred quite robustly to be about7.5h−1Mpc,without much dependence on the rate of evolution.Since the strength of clustering for optical galaxies at z=1is known to correspond to the much smaller number of r0≃2h−1Mpc(e.g.Le F`e vre et al.1996),we see that radio galaxies at this redshift have a relative bias parameter of close to 3.The explanation for this high degree of bias is probably similar to that which applies in the case of QSOs:in both cases we are dealing with AGN hosted by rare massive galaxies.3.Formation and bias of high-redshift galaxiesThe challenge now is to ask how these results can be understood in cur-rent models for cosmological structure formation.It is widely believed that the sequence of cosmological structure formation was hierarchical,originating in a density power spectrum with increasingﬂuctuations on small scales.The large-wavelength portion of this spectrum is accessible to observation today through studies of galaxy clustering in the linear and quasilinear regimes.However,non-linear evolution has eﬀectively erased any information on the initial spectrum for wavelengths below about1Mpc.The most sensitive way of measuring the spectrum on smaller scales is via the abundances of high-redshift objects;the amplitude ofﬂuctuations on scales of individual galaxies governs the redshift at which these objectsﬁrst undergo gravitational collapse.The small-scale am-plitude also inﬂuences clustering,since rare early-forming objects are strongly correlated,asﬁrst realized by Kaiser(1984).It is therefore possible to use obser-vations of the abundances and clustering of high-redshift galaxies to estimate the power spectrum on small scales,and the following section summarizes the results of this exercise,as given by Peacock et al.(1998).(a)Press-Schechter apparatusThe standard framework for interpreting the abundances of high-redshift objects in terms of structure-formation models,was outlined by Efstathiou& Rees(1988).The formalism of Press&Schechter(1974)gives a way of calculating the fraction F c of the mass in the universe which has collapsed into objects more massive than some limit M:F c(>M,z)=1−erf δc2σ(M) .(3.1)8J.A.PeacockHere,σ(M)is the rms fractional density contrast obtained byﬁltering the linear-theory densityﬁeld on the required scale.In practice,thisﬁltering is usually performed with a spherical‘top hat’ﬁlter of radius R,with a corresponding mass of4πρb R3/3,whereρb is the background density.The numberδc is the linear-theory critical overdensity,which for a‘top-hat’overdensity undergoing spherical collapse is1.686–virtually independent ofΩ.This form describes numerical simulations very well(see e.g.Ma&Bertschinger1994).The main assumption is that the densityﬁeld obeys Gaussian statistics,which is true in most inﬂationary models.Given some estimate of F c,the numberσ(R)can then be inferred.Note that for rare objects this is a pleasingly robust process:a large error in F c will give only a small error inσ(R),because the abundance is exponentially sensitive toσ.Total masses are of course ill-deﬁned,and a better quantity to use is the velocity dispersion.Virial equilibrium for a halo of mass M and proper radius r demands a circular orbital velocity ofV2c=GMΩ1/2m(1+z c)1/2f 1/6c.(3.3)Here,z c is the redshift of virialization;Ωm is the present value of the matter density parameter;f c is the density contrast at virialization of the newly-collapsed object relative to the background,which is adequately approximated byf c=178/Ω0.6m(z c),(3.4) with only a slight sensitivity to whetherΛis non-zero(Eke,Cole&Frenk1996).For isothermal-sphere haloes,the velocity dispersion isσv=V c/√The evolution of galaxy clustering and bias9 and the more recent estimate of0.025from Tytler et al.(1996),thenΩHIF c=2for the dark halo.A more recent measurement of the velocity width of the Hαemission line in one of these objects gives a dispersion of closer to100km s−1(Pettini,private communication),consistent with the median velocity width for Lyαof140km s−1 measured in similar galaxies in the HDF(Lowenthal et al.1997).Of course,these ﬁgures could underestimate the total velocity dispersion,since they are dominated by emission from the central regions only.For the present,the range of values σv=100to320km s−1will be adopted,and the sensitivity to the assumed velocity will be indicated.In practice,this uncertainty in the velocity does not produce an important uncertainty in the conclusions.(3)Red radio galaxies An especially interesting set of objects are the reddest optical identiﬁcations of1-mJy radio galaxies,for which deep absorption-line spectroscopy has proved that the red colours result from a well-evolved stellar population,with a minimum stellar age of3.5Gyr for53W091at z=1.55(Dun-10J.A.Peacocklop et al.1996;Spinrad et al.1997),and4.0Gyr for53W069at z=1.43(Dunlop 1998;Dey et al.1998).Such ages push the formation era for these galaxies back to extremely high redshifts,and it is of interest to ask what level of small-scale power is needed in order to allow this early formation.Two extremely red galaxies were found at z=1.43and1.55,over an area 1.68×10−3sr,so a minimal comoving density is from one galaxy in this redshift range:N(Ω=1)>∼10−5.87(h−1Mpc)−3.(3.9) Thisﬁgure is comparable to the density of the richest Abell clusters,and is thus in reasonable agreement with the discovery that rich high-redshift clusters appear to contain radio-quiet examples of similarly red galaxies(Dickinson1995).Since the velocity dispersions of these galaxies are not observed,they must be inferred indirectly.This is possible because of the known present-day Faber-Jackson relation for ellipticals.For53W091,the large-aperture absolute magni-tude isM V(z=1.55|Ω=1)≃−21.62−5log10h(3.10) (measured direct in the rest frame).According to Solar-metallicity spectral syn-thesis models,this would be expected to fade by about0.9mag.between z=1.55 and the present,for anΩ=1model of present age14Gyr(note that Bender et al.1996have observed a shift in the zero-point of the M−σv relation out to z=0.37of a consistent size).If we compare these numbers with theσv–M V relation for Coma(m−M=34.3for h=1)taken from Dressler(1984),this predicts velocity dispersions in the rangeσv=222to292km s−1.(3.11) This is a very reasonable range for a giant elliptical,and it adopted in the following analysis.Having established an abundance and an equivalent circular velocity for these galaxies,the treatment of them will diﬀer in one critical way from the Lyman-αand Lyman-limit galaxies.For these,the normal Press-Schechter approach as-sumes the systems under study to be newly born.For the Lyman-αand Lyman-limit galaxies,this may not be a bad approximation,since they are evolving rapidly and/or display high levels of star-formation activity.For the radio galax-ies,conversely,their inactivity suggests that they may have existed as discrete systems at redshifts much higher than z≃1.5.The strategy will therefore be to apply the Press-Schechter machinery at some unknown formation redshift,and see what range of redshift gives a consistent degree of inhomogeneity.4.The small-scaleﬂuctuation spectrum(a)The empirical spectrumFig.2shows theσ(R)data which result from the Press-Schechter analysis, for three cosmologies.Theσ(R)numbers measured at various high redshifts have been translated to z=0using the appropriate linear growth law for density perturbations.The open symbols give the results for the Lyman-limit(largest R)and Lyman-α(smallest R)systems.The approximately horizontal error bars showThe evolution of galaxy clustering and bias11Figure2.Theradius R.Thecircles)Theredshifts2,4,...The horizontal errors correspond to diﬀerent choices for the circular velocities of the dark-matter haloes that host the galaxies.The shaded region at large R gives the results inferred from galaxy clustering.The lines show CDM and MDM predictions,with a large-scale normalization ofσ8=0.55forΩ=1orσ8=1for the low-density models.the eﬀect of the quoted range of velocity dispersions for aﬁxed abundance;the vertical errors show the eﬀect of changing the abundance by a factor2atﬁxed velocity dispersion.The locus implied by the red radio galaxies sits in between. The diﬀerent points show the eﬀects of varying collapse redshift:z c=2,4,...,12 [lowest redshift gives lowestσ(R)].Clearly,collapse redshifts of6–8are favoured12J.A.Peacockfor consistency with the other data on high-redshift galaxies,independent of the-oretical preconceptions and independent of the age of these galaxies.This level of power(σ[R]≃2for R≃1h−1Mpc)is also in very close agreement with the level of power required to produce the observed structure in the Lyman alpha forest(Croft et al.1998),so there is a good case to be made that theﬂuctu-ation spectrum has now been measured in a consistent fashion down to below R≃1h−1Mpc.The shaded region at larger R shows the results deduced from clustering data (Peacock1997).It is clear anΩ=1universe requires the power spectrum at small scales to be higher than would be expected on the basis of an extrapolation from the large-scale spectrum.Depending on assumptions about the scale-dependence of bias,such a‘feature’in the linear spectrum may also be required in order to satisfy the small-scale present-day nonlinear galaxy clustering(Peacock1997). Conversely,for low-density models,the empirical small-scale spectrum appears to match reasonably smoothly onto the large-scale data.Fig.2also compares the empirical data with various physical power spectra.A CDM model(using the transfer function of Bardeen et al.1986)with shape parameterΓ=Ωh=0.25is shown as a reference for all models.This appears to have approximately the correct shape,although it overpredicts the level of small-scale power somewhat in the low-density cases.A better empirical shape is given by MDM withΩh≃0.4andΩν≃0.3.However,this model only makes physical sense in a universe with highΩ,and so it is only shown as the lowest curve in Fig.2c,reproduced from theﬁtting formula of Pogosyan&Starobinsky(1995; see also Ma1996).This curve fails to supply the required small-scale power,by about a factor3inσ;loweringΩνto0.2still leaves a very large discrepancy. This conclusion is in agreement with e.g.Mo&Miralda-Escud´e(1994),Ma& Bertschinger(1994),Ma et al.(1997)and Gardner et al.(1997).All the models in Fig.2assume n=1;in fact,consistency with the COBE results for this choice ofσ8andΩh requires a signiﬁcant tilt forﬂat low-density CDM models,n≃0.9(whereas open CDM models require n substantially above unity).Over the range of scales probed by LSS,changes in n are largely degenerate with changes inΩh,but the small-scale power is more sensitive to tilt than to Ωh.Tilting theΩ=1models is not attractive,since it increases the tendency for model predictions to lie below the data.However,a tilted low-Ωﬂat CDM model would agree moderately well with the data on all scales,with the exception of the ‘bump’around R≃30h−1Mpc.Testing the reality of this feature will therefore be an important task for future generations of redshift survey.(b)Collapse redshifts and ages for red radio galaxiesAre the collapse redshifts inferred above consistent with the age data on the red radio galaxies?First bear in mind that in a hierarchy some of the stars in a galaxy will inevitably form in sub-units before the epoch of collapse.At the time ofﬁnal collapse,the typical stellar age will be some fractionαof the age of the universe at that time:age=t(z obs)−t(z c)+αt(z c).(4.1) We can rule outα=1(i.e.all stars forming in small subunits just after the big bang).For present-day ellipticals,the tight colour-magnitude relation only allows an approximate doubling of the mass through mergers since the termination ofThe evolution of galaxy clustering and bias13Figure3.The age of a galaxy at z=1.5,as a function of its collapse redshift(assuming an instantaneous burst of star formation).The various lines showΩ=1[solid];openΩ=0.3 [dotted];ﬂatΩ=0.3[dashed].In all cases,the present age of the universe is forced to be14 Gyr.star formation(Bower at al.1992).This corresponds toα≃0.3(Peacock1991).A non-zeroαjust corresponds to scaling the collapse redshift asapparent(1+z c)∝(1−α)−2/3,(4.2) since t∝(1+z)−3/2at high redshifts for all cosmologies.For example,a galaxy which collapsed at z=6would have an apparent age corresponding to a collapse redshift of7.9forα=0.3.Converting the ages for the galaxies to an apparent collapse redshift depends on the cosmological model,but particularly on H0.Some of this uncertainty may be circumvented byﬁxing the age of the universe.After all,it is of no interest to ask about formation redshifts in a model with e.g.Ω=1,h=0.7when the whole universe then has an age of only9.5Gyr.IfΩ=1is to be tenable then either h<0.5against all the evidence or there must be an error in the stellar evolution timescale.If the stellar timescales are wrong by aﬁxed factor,then these two possibilities are degenerate.It therefore makes sense to measure galaxy ages only in units of the age of the universe–or,equivalently,to choose freely an apparent Hubble constant which gives the universe an age comparable to that inferred for globular clusters.In this spirit,Fig.3gives apparent ages as a function of eﬀective collapse redshift for models in which the age of the universe is forced to be14 Gyr(e.g.Jimenez et al.1996).This plot shows that the ages of the red radio galaxies are not permitted very much freedom.Formation redshifts in the range6to8predict an age of close to 3.0Gyr forΩ=1,or3.7Gyr for low-density models,irrespective of whetherΛis nonzero.The age-z c relation is ratherﬂat,and this gives a robust estimate of age once we have some idea of z c through the abundance arguments.It is therefore14J.A.Peacockrather satisfying that the ages inferred from matching the rest-frame UV spectra of these galaxies are close to the aboveﬁgures.(c)The global picture of galaxy formationIt is interesting to note that it has been possible to construct a consistent picture which incorporates both the large numbers of star-forming galaxies at z<∼3and the existence of old systems which must have formed at very much larger redshifts.A recent conclusion from the numbers of Lyman-limit galaxies and the star-formation rates seen at z≃1has been that the global history of star formation peaked at z≃2(Madau et al.1996).This leaves open two possibilities for the very old systems:either they are the rare precursors of this process,and form unusually early,or they are a relic of a second peak in activity at higher redshift,such as is commonly invoked for the origin of all spheroidal components. While such a bimodal history of star formation cannot be rejected,the rareness of the red radio galaxies indicates that there is no diﬃculty with the former picture. This can be demonstrated quantitatively by integrating the total amount of star formation at high redshift.According to Madau et al.,The star-formation rate at z=4is˙ρ∗≃107.3h M⊙Gyr−1Mpc−3,(4.3) declining roughly as(1+z)−4.This is probably a underestimate by a factor of at least3,as indicated by suggestions of dust in the Lyman-limit galaxies(Pettini et al.1997),and by the prediction of Pei&Fall(1995),based on high-z element abundances.If we scale by a factor3,and integrate toﬁnd the total density in stars produced at z>6,this yieldsρ∗(z f>6)≃106.2M⊙Mpc−3.(4.4) Since the red mJy galaxies have a density of10−5.87h3Mpc−3and stellar masses of order1011M⊙,there is clearly no conﬂict with the idea that these galaxies are theﬁrst stellar systems of L∗size which form en route to the general era of star and galaxy formation.(d)Predictions for biased clustering at high redshiftsAn interesting aspect of these results is that the level of power on1-Mpc scales is only moderate:σ(1h−1Mpc)≃2.At z≃3,the correspondingﬁgure would have been much lower,making systems like the Lyman-limit galaxies rather rare.For Gaussianﬂuctuations,as assumed in the Press-Schechter analysis,such systems will be expected to display spatial correlations which are strongly biased with respect to the underlying mass.The linear bias parameter depends on the rareness of theﬂuctuation and the rms of the underlyingﬁeld asb=1+ν2−1δc(4.5)(Kaiser1984;Cole&Kaiser1989;Mo&White1996),whereν=δc/σ,andσ2is the fractional mass variance at the redshift of interest.In this analysis,δc=1.686is assumed.Variations in this number of order10 per cent have been suggested by authors who have studied theﬁt of the Press-Schechter model to numerical data.These changes would merely scale b−1by a small amount;the key parameter isν,which is set entirely by the collapsed。

好奇研星象的英语作文

Curiosity has always been a driving force behind human exploration and discovery. In the realm of astronomy,this innate desire to understand the cosmos has led to remarkable advancements in our knowledge of the universe.The English essay on the curiosity about celestial phenomena can delve into various aspects of this pursuit,from the early days of stargazing to the modern era of space exploration.In ancient times,people gazed at the night sky with wonder,trying to make sense of the celestial bodies they observed.The patterns they saw in the stars led to the creation of constellations,which were used for navigation,timekeeping,and even as a means to tell stories and pass on cultural knowledge.The essay could explore the significance of these early observations and how they shaped human understanding of the cosmos.As time progressed,so did our tools for observing the heavens.The invention of the telescope in the early17th century by Hans Lippershey marked a significant leap in astronomical research.The essay could discuss the impact of this invention on our understanding of the universe,highlighting the contributions of astronomers like Galileo Galilei,who used the telescope to observe the moons of Jupiter and the phases of Venus, challenging the geocentric model of the universe.The curiosity about celestial phenomena also led to the development of various theories and laws that govern the motion of celestial bodies.The essay could delve into the work of Sir Isaac Newton,who formulated the laws of motion and universal gravitation, providing a comprehensive framework for understanding the movements of planets and stars.In the20th century,our curiosity about the stars took us beyond our own solar system. The essay could discuss the contributions of astronomers like Edwin Hubble,who discovered the expansion of the universe and the existence of other galaxies beyond the Milky Way.This revelation opened up a whole new realm of questions and curiosity about the nature and origins of the cosmos.The advent of space exploration has further fueled our curiosity about celestial phenomena.The essay could explore the significance of manned and unmanned space missions,such as the Apollo moon landings and the Voyager spacecraft,which have provided us with unprecedented insights into our solar system and beyond. Moreover,the curiosity about stars has also led to the discovery of exoplanets and the ongoing search for extraterrestrial life.The essay could discuss the implications of these discoveries for our understanding of life in the universe and the potential for future exploration.In conclusion,the curiosity about celestial phenomena has been a catalyst for human progress in astronomy.From the early days of stargazing to the modern era of space exploration,our desire to understand the cosmos has led to remarkable discoveries and advancements.The essay could emphasize the importance of maintaining this curiosity and continuing to explore the mysteries of the universe.。

Metals in Star-Forming Galaxies at High Redshift

a rXiv:as tr o-ph/56285v113J un25From Lithium to Uranium:Elemental Tracers of Early Cosmic Evo-lution Proceedings IAU Symposium No.228,2005V.Hill,P.Fran¸c ois &F.Primas,eds.c 2005International Astronomical Union DOI:00.0000/X000000000000000X Metals in Star-Forming Galaxies at High Redshift Claus Leitherer Space Telescope Science Institute,3700San Martin Dr.,Baltimore,MD 21218,USA email:leitherer@ Abstract.The chemical composition of high-redshift galaxies is an important property that gives clues to their past history and future evolution.Measuring abundances in distant galaxies with current techniques is often a challenge,and the canonical metallicity indicators can often not be applied.I discuss currently available metallicity indicators based on stellar and interstellar absorption and emission lines,and assess their limitations and systematic uncertainties.Recent studies suggest that star-forming galaxies at redshift around 3have heavy-element abundances already close to solar,in agreement with predictions from cosmological models.Keywords.galaxies:abundances,galaxies:high-redshift,galaxies:starburst,ultraviolet:galax-ies2Claus Leithererparison between the observed spectrum of MS1512–cB58(solid)and two syn-thetic models with1/4Z⊙(lower;dashed)and Z⊙(upper;dotted).The models have continuous star formation,age100Myr,and Salpeter IMF between1and100M⊙.The stellar lines are weaker in the metal-poor model(from Leitherer et al.2001).3.Techniques—Restframe Optical versus UVAbundance determinations typically fall into two categories,either relying on indica-tors in the restframe optical,or on those in the restframe UV.The restframe optical wavelength region has traditionally been used to determine galaxy abundances from nebular emission lines.At a redshift of z=3,the restframe optical is observed in the near-infrared(IR)H and K bands.Spectroscopic observations of LBGs in the near-IR have become technically feasible(e.g.,Pettini et al.2001)but abundance analyses are still challenging.Only the strongest lines such as,e.g.,Hα,Hβ,[N II]λ6584,or[O III]λ5007are detectable at suﬃcient S/N.Even when good-quality spectra are available,the atmospheric windows usually restrict the wavelengths to a narrow range,which precludes commonly used techniques such as the classical R23strong-line method(McGaugh1991). The need for alternative variants of the classical strong-line method led Pettini&Pagel (2004)to readdress the usefulness of the N2and O3N2ratios.The former is deﬁned as the ratio[N II]λ6584over Hαand was recently discussed by Denicol´o et al.(2002);the latter includes the oxygen line for the ratio([O III]λ5007/Hβ)/([N II]λ6584/Hα)and was originally introduced by Alloin et al.(1979).After calibrating the two abundance indicators with a local H II region sample,Pettini&Pagelﬁnd that O3N2and N2predict O/H to within0.25dex and0.4dex at the2σconﬁdence level,respectively.The observed frame optical wavelength region corresponds to the restframe UV of LBGs.The UV contains few nebular emission lines in star-forming galaxies(Leitherer 1997)and has rarely been used for chemical composition studies in local galaxies of this type.Fig.1compares the UV spectrum of the LBG MS1512–cB58with theoretical spectra(Leitherer et al.2001).Three groups of lines can be distinguished:(i)Interstellar absorption lines,most of which are strong and heavily saturated.Only in very few cases can unsaturated absorption lines in LBGs be used for an abundance analysis.(ii)Broad stellar-wind lines with emission and blueshifted absorption.These lines are the telltales of massive OB stars whose stellar winds are metallicity dependent.(iii)Weak photospheric absorption lines which can only be seen in high-quality spectra.Abundance studies from stellar lines in restframe UV spectra must rely either on suitable template stars or on extensive non-LTE radiation-hydrodynamic models which are only beginning to become available(Rix et al.2004).Metals in High-z Galaxies3 4.The Chemical Composition of LBGsAn initial,rough estimate of the heavy-element abundances can be obtained from the equivalent widths of the strong UV absorption lines.Heckman et al.(1998)pointed out the close correlation of the Si IVλ1400and C IVλ1550equivalent widths with O/H in a sample of local star-forming galaxies.This correlation seems surprising,as these stellar-wind lines are deeply saturated.The reason for the metallicity dependence is the behavior of stellar winds in diﬀerent chemical environments.At lower abundance,the winds are weaker and have lower velocity,and the lines become weaker and narrower.As a result,the equivalent widths are smaller at lower O/H.If the same correlation holds at high redshift,the observed equivalent widths in LBGs suggest[O/H]≃–0.5(Leitherer 1999).A similar,somewhat weaker correlation exists between O/H and the equivalent widths of the strongest interstellar lines.This is even more unexpected because the equivalent widths of saturated lines have essentially no dependence on the column density N ion:W∝b[ln(N ion/b)]0.5.Therefore the correlation must be caused by the b factor, and therefore by velocity.More metal-rich galaxies are thought to host more powerful starbursts with correspondingly larger mechanical energy release by stellar winds and supernovae.The energy input leads to increased macroscopic turbulence and higher gas velocities at higher O/H(Heckman et al.1998).If the same applies to star-forming galaxies in the high-redshift universe,their measured equivalent widths again indicate an oxygen abundance of about1/3the solar value.Pettini et al.(2001)determined oxygen abundances inﬁve LBGs from emission lines in restframe optical spectra.The redshift range of the sample dictated the use of the R23 method.The galaxies turned out to be rather metal-rich,with O/H somewhat below the solar value.This is roughly in agreement with restframe UV results,and an order of magnitude above the metallicities found in damped Lyman-αabsorbers(DLA)which are found at the same redshift.Because of the double-valued nature of the R23method, the possibility exists but is deemed less likely that the sample has oxygen abundances of only1/10the solar value.The lensed LBG MS1512–cB58and its bright restframe UV spectrum can be studied at suﬃciently high S/N and resolution to detect and resolve faint,unsaturated interstellar absorption lines.Pettini et al.(2002)measured numerous transitions from H to Zn cov-ering several ionization stages.Abundances of several key elements could be derived.The α-elements O,Mg,Si,P,and S all have abundances of about40%solar,indicating that the interstellar medium is highly enriched in the chemical elements produced by type II supernovae.In contrast,N and the Fe-peak elements Mn,Fe,and Ni are all less abundant than expected by factors of several.In standard chemical evolution models,most of the nitrogen is produced by intermediate-mass stars,whereas type Ia supernovae contribute most of the Fe-peak elements.Since the evolutionary time scales of intermediate-and low-mass stars are signiﬁcantly longer than those of massive stars producing theα-elements, the release of N and the Fe-group elements into the interstellar medium is delayed by ∼109yr.MS1512–cB58may be an example of a star-forming galaxy in its early stage of chemical enrichment,consistent with its cosmological age of only about15%of the age of the universe.Mehlert et al.(2002)provided similar arguments to explain variation of the C IVλ1550line relative to Si IVλ1400in a small sample of LBGs.C IV appears to decrease in strength relative to Si IV from lower to higher redshift,which may reﬂect the time delay of the carbon release by intermediate-mass stars.The interstellar lines in LBGs have blueshifts with velocities of up to several hun-dred km s−1indicating large-scale outﬂows.The associated galactic mass-loss rates of ∼102M⊙yr−1are comparable to the rates of star formation.The newly formed heavy4Claus LeithererFigure2.Left pair of panels:comparison of the observed spectrum of MS1512–cB58(thick) with fully synthetic spectra(thin)forﬁve diﬀerent metallicities,from twice solar to1/20solar. First panel:region around1425˚A;second:region of the Fe III blend near1978˚A.Each pair of panels is labeled with the metallicity of the synthetic spectrum shown.Right pair of panels: same as left pair,but for Q1307–BM1163(from Rix et al.2004).elements are removed from their birth sites by stellar winds and supernovae and are trans-ported into the halo and possibly into the intergalactic medium(Pettini et al.2002). Detailed studies of weak interstellar lines such as that done for MS1512–cB58remain a technical challenge,even for high-throughput spectrographs at the largest telescopes. Furthermore,the results for Fe-peak elements carry some uncertainty because of the a priori unknown depletion corrections.Abundance analyses using stellar lines are not aﬀected by depletion uncertainties.However,the existence of non-standard element ratios precludes the use of locally observed template spectra for spectral synthesis.Therefore our group(F.Bresolin,R.Kudritzki,C.Leitherer,M.Pettini,S.Rix)has embarked on a project to model the spectra of hot stars and link them with a spectral synthesis code to predict the emergent UV spectrum of a composite stellar population as a function of metallicity.We generated a grid of hydrodynamic non-LTE atmospheres with the WM-basic code(Pauldrach et al.2001)and calculated the corresponding UV line spectra.The resulting library was incorporated into the Starburst99code(Leitherer et al.1999)which then allowed us to compute a suite of model spectra for appropriate stellar population parameters.As aﬁrst application,we used several faint stellar blends around1425˚A and 1978˚A as a metallicity indicator(Rix et al.2004).The1425˚A feature is a blend of Si III, C III,and Fe V,and the1978˚A absorption is mainly Fe III.The synthesized spectra for ﬁve metallicities are compared to the observed restframe UV spectra of MS1512–cB58 and Q1307–BM1163in Fig.2.The model having40%solar metal abundance provides the bestﬁt to the data,in agreement with the results from other methods.A variety of independent techniques lead to consistent results for the chemical com-position of LBGs.While each method by itself is subject to non-negligible uncertainties,Metals in High-z Galaxies5Figure3.Metallicity-luminosity relationship.Data for local spiral and irregular galaxies are from Garnett(2002).The z=2objects are overluminous for their(O/H)abundances,derived using the N2calibration of Pettini&Pagel(2004)but lie closer to the relationship for the local galaxies than z=3LBGs(from Shapley et al.2004).the overall agreement of the results gives conﬁdence in the derived abundances.LBGs at z≃3have heavy-element abundances of about1/3the solar value.5.Cosmological PerspectiveStar-forming galaxies at z≃3,at an epoch when the universe’s age was only15% the present value,display a high level of chemical enrichment.What does their chemical composition tell us about their relation to other galaxies at lower redshift and to other structures found at z=3?Galaxies at somewhat lower redshift have only recently become accessible for detailed study due to the combined challenges of instrumentation and the galactic spectral prop-erties.Shapley et al.(2004)obtained K-band spectroscopy of seven UV-selected star-forming galaxies at redshifts between2and2.5.The N2method calibrated by Pettini &Pagel(2004)was used as an abundance diagnostic.When compared to the original higher-z LBGs,the z≃2sample is more metal-rich.This can be seen in Fig.3,where O/H of the z=2galaxies is compared with that of LBGs at z≃3and of local star-forming galaxies over a range of blue luminosities.The latter were analyzed with the R23method.The z=2sample has almost solar chemical composition but is still less metal-rich than local late-type galaxies with comparable luminosities.As a caveat,the comparison rests on the assumption that the N2and R23calibrations have no signiﬁcant oﬀset.The diﬀerence between the average redshift of the LBG sample and of the z=2 galaxies translates into a mean age diﬀerence of about1Gyr.Both the chemical proper-ties and the masses of the z=2galaxies and LBGs are consistent with standard passive evolution models.Kewley&Kobulnicky(2005)followed the metallicity evolution of star-forming galaxies with comparable luminosities from z=0to3.5.O/H was determined from restframe optical emission lines using the strong-line method in four homogeneous galaxy samples. The samples were taken from the CfA2survey,from the GOODSﬁeld,from Shapley et al.(2004),and from the LBG sample,covering z≈0,0.7,2.1−2.5,and2.5−3.5, respectively.The average oxygen abundance in the local universe,as deﬁned by the CfA2 sample is about solar.O/H decreases with redshift to approximately1/3solar at z=3.6Claus LeithererIt is instructive to compare the heavy-element abundances of LBGs to those of DLAs and to the Lyman-forest at the same redshift(Pettini2004).DLA systems have metallic-ities of about1/15Z⊙and are thought to be the cross sections of the outer regions and halos of(proto)-galaxies seen along the sightlines of quasars.Although the properties of LBGs and DLAs do not immediately support a close relation between the two classes of objects,at least some link seems likely.If so,the observed outﬂows in LBGs may provide the metal enrichment of the halos.The Lyman-forest is predicted by cold dark matter models to result from structure formation in the presence of an ionizing background. The Lyman-forest had long been thought to be truly primordial,but metal enrichment of1/100–1/1000Z⊙has recently been detected(Aguirre et al.2004).This relatively high metal abundance early in the evolution of the universe could have been produced by aﬁrst generation of Population III stars.Such stars can account for the amount of metals,and at the same time could have provided copious ionizing photons,as metal and photon production are closely correlated.Alternatively,star-forming galaxies at high redshift could be the production sites of the metals seen in the intergalactic medium if superwinds are capable of removing the newly formed metals from galactic disks. AcknowledgementsI would like to thank Max Pettini for a careful reading of the manuscript and for providing invaluable comments.ReferencesAguirre,A.,Schaye,J.,Kim,T.,Theuns,T.,Rauch,M.,&Sargent,W.2004,ApJ,602,38 Alloin,D.,Collin-Souﬀrin,S.,Joly,M.,&Vigroux L.1979,A&A,78,200Denicol´o,G.,Terlevich,R.,&Terlevich,E.2002,MNRAS,330,69Garnett,D.R.2002,ApJ,581,1019Giavalisco,M.2002,ARAA,40,579Heckman,T.M.,Robert,C.,Leitherer,C.,Garnett,D.,&van de Rydt,F.1998,ApJ,503,646 Kewley,L.,&Kobulnicky,H.A.2005,in R.de Grijs&R.M.Gonz´a lez Delgado(eds.),Star-bursts:From30Doradus to Lyman Break Galaxies,(Dordrecht:Springer),p.307 Kulkarni,V.P.,Fall,S.M.,Lauroesch,J.T.,York,D.G.,Welty,D.E.,Khare,P.,&Truran, J.W.2005,ApJ,618,68Leitherer,C.1997,in:W.H.Waller,M.N.Fanelli,J.E.Hollis,&A.C.Danks(eds.),The Ultraviolet Universe at Low and High Redshift:,(Woodbury:AIP),p.119Leitherer,C.1999,in:J.Walsh&M.Rosa(eds.),Chemical Evolution from Zero to High Redshift, (Berlin:Springer),p.204Leitherer,C.,Le˜a o,J.R.S.,Heckman,T.M.,Lennon,D.J.,Pettini,M.,&Robert,C.2001, ApJ,550,724Leitherer,C.,et al.1999,ApJS,123,3McGaugh,S.1991,ApJ,380,140Mehlert,D.,et al.2002,A&A,393,809Pauldrach,A.W.A.,Hoﬀmann,T.L.,&Lennon,M.2001,A&A,375,161Pettini,M.2004,in:C.Esteban,R.J.Garc´ıa L´o pez,A.Herrero,&F.S´a nchez(eds.),Cosmo-chemistry,XIII Canary Islands Winter School,(Cambridge:CUP),p.257Pettini,M.,Rix,S.A.,Steidel,C.C.,Adelberger,K.L.,Hunt,M.P.,&Shapley,A.E.2002, ApJ,569,742Pettini,M.,Shapley,A.E.,Steidel,C.C.,Cuby,J.,Dickinson,M.,Moorwood,A.F.M., Adelberger,K.L.,&Giavalisco,M.2001,ApJ,554,981Rix,S.A.,Pettini,M.,Leitherer,C.,Bresolin,F.,Kudritzki,R.,&Steidel,C.C.2004,ApJ, 615,98Shapley,A.E.,Erb,D.K.,Pettini,M.,Steidel,C.C.,&Adelberger,K.L.2004,ApJ,612,108 Steidel,C.C.,Adelberger,K.L.,Giavalisco,M.,Dickinson,M.&Pettini,M.1999,ApJ,519,1。

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a rXiv:as tr o-ph/38543v129Aug23SEARCHES FOR HIGH REDSHIFT GALAXIES USING GRA VITATIONAL LENSING J.Richard 1,R.Pello 1,J.-P.Kneib 1,2,D.Schaerer 1,3,M.R.Santos 2,R.Ellis 21O.M.P .,Laboratoire d’Astrophysique,UMR 5572,14Avenue E.Belin,31400Toulouse,France 2California Institute of Technology,105-24Caltech,Pasadena,CA 91125,USA 3Geneva Observatory,51Ch.des Maillettes,CH-1290Sauverny,Switzerland jrichard@ast.obs-mip.fr Abstract We present different methods used to identify high redshift (z >5)objects in the high-magniﬁcation regions of lensing galaxy clusters,taking advantage of very well constrained lensing models.The research procedures are explained and discussed.The detection of emission lines in the optical/NIR spectra,such as Lyman-alpha,allows us to determine the redshift of these sources.Thanks to the lensing magniﬁcation,it is possible to identify and to study more distant or intrinsically fainter objects with respect to standard ﬁeld surveys.Keywords:galaxies:formation,evolution,high-redshift,luminosity function,clusters :lensing —cosmology:observations Introduction The main purpose of looking at high redshift (z >5)objects is to get con-straints about the nature and the formation epoch of the ﬁrst sources in the Universe.The advent of 8-10m class telescopes,such as VLT and Keck,hasopened up this ﬁeld of study.Moreover,the use of clusters of galaxies as grav-itational telescopes can help a lot for this.Strong lensing effect in clusters has already enabled the detection of one of the most distant galaxies known up to now (Hu et al.2002),thanks to the gravitational magniﬁcation and despite the decrease in effective area of the survey.We present here two methods aimed at the detection of lyman-alpha sources behind galaxy clusters :ﬁrst a spectroscopic search along the critical lines of clusters,and then a photometric selection technique for very low metallicity starbursts (the so-called Population III objects,Loeb &Barkana 2001),using ultra-deep near infrared imaging.2Critical lines surveyUsing the LRIS spectrograph at Keck,we searched for Lyαemitters at red-shift2.5to6.8in the most magniﬁed parts of a sample of lensing clusters,selected for having well-constrained mass models.We scanned the regionslocated near the critical lines(Figure1),deﬁned as the lines of inﬁnite mag-niﬁcation for a given redshift,using a175"-long slit.Half of the area covered(4.2arcmin2)is at least magniﬁed by a factor of10at z=5.We systematically looked for every single emission line in the spectra,andwe conﬁrmed Lyαcandidates using HST images available for these clusters,optical photometry,and further spectroscopy at higher resolution,using ESI atKeck that can easily resolve the[OII]doublet,thus preventing this contamina-tion.We identiﬁed12Lyαcandidates,three of them lying in the redshift range∼4.6−5.6.One is a double image at z∼5.6which was analysed with more details by Ellis et.al(2001).The two-dimensionnal LRIS spectra,showingLyαemission lines,are presented inﬁgure1.Thanks to the strong lensing magniﬁcation,these results can give us con-straints on the luminosity function of emitters at4.6<z<5.6with Lyαluminosity1040<L<1042erg/s,which is a depth that was not reached by other surveys of Lyαemitters or Lyman Break Galaxies.This will be pre-sented in Santos et al.(2003,ApJ submitted).Figure1.On the left:zoom on the center part of the galaxy cluster Abell2218.The critical lines for z=5are shown as dashed lines,and the two regions scanned by the survey as rectangles. On the right:composite spectra of the three Lyαemitters(circled)found at z∼5−6.Searches for high redshift galaxiesusing gravitational lensing3 Looking for Population III objectsRecent models by D.Schaerer(2002,2003)for the Spectral Energy Distri-butions(SED)of Population III objects show that they may be currently ob-servable using8-10m telescopes,at the limits of conventional spectroscopy. The identiﬁcation of such objects should be possible thanks to their very strong emission lines,mainly Lyαand HeIIλ1640.In order toﬁnd these objects,the colors predicted by the same models can allow us to deﬁne a color-color region in the near-infrared diagram(J-H)vs(H-K’),where we can pick up candidates (Fig.2).By doing simulations with existing models,we found that we should not be contaminated by stars or z<8galaxies,even in the case of important redenning.As aﬁrst test of these selection criteria,we did very deep imaging(limiting magnitudes of J=25,H=24.5,K’=24,Vega system),with ISAAC on VLT,of two lensing clusters,taking advantage of the lensing magniﬁcation to help us detecting these faint objects.Preliminary resultsWe selected several(∼10)candidates per cluster,satisfying our selection criteria in the near-IR,and being undetected on available optical images.These objects have the expected magnitudes and SEDs of8<z<10Population III objects(Figure2),and are magniﬁed by2to4magnitudes thanks to the strong lensing effect.We used a modiﬁed version of the photometric software hyperz(Bolzonella et al.2000)toﬁnd the redshift distribution probability of our candidates with the spectra models quoted above.Figure2.Left:location,on the NIR color-color diagram(J-H)vs(H-K’),of the candidates found with the typical photometric errors(Vega system).The selection region for Population III objects is delimited by a solid line.Right:example of SED,combining infrared and optical photometry,for one of the candidates.Photometric redshift gives z∼9.As a preliminary result,we can try to compare the number of Population III objects per redshift that was expected to be detected in ourﬁeld with the upper4limit corresponding to our candidates,using a simple model of dark-matter halos distribution(Press&Schechter,1974),and4different models of IMF for PopIII galaxies(Figure3).Furthermore,we can estimate the efﬁciency of using strong lensing in thisﬁeld by plotting the expected number counts in a blankﬁeld of same size and depth.Weﬁnd that lensing is more efﬁcient at high redshifts(z>8),and that the number of candidates we found is consistent with some of the models we used.ConclusionsThe use of gravitational lensing is efﬁcient to detect more distant or intrinsi-cally fainter galaxies lying behind galaxy clusters:we can have constraints on luminosity functions at fainter scales,and the expected number of primordial objects in a clusterﬁeld is boosted at high redhsifts.Even if the candidates we found with our selection criteria are very faint,we should try to perform spectroscopy of the best ones with present day facilities. The detection of these sources is one of the major science cases for the next generation NIR instruments,like EMIR/GTC,KMOS/VLT or KIRMOS/Keck.Figure3.Number counts of PopIII objects per interval of0.1in z,expected to have K’<24in the ISAAC fov.The different curves correspond to different IMF models.The values obtained with gravitational lensing(solid curves)are boosted by a factor of10at z∼8−10regarding the one expected for a blankﬁeld(dashed curves).Overplotted is the upper limit of our survey. ReferencesBolzonella,M.,Miralles,J.M.,Pello,R.,2000,A&A,363,476Ellis,R.,Santos,M.R.,Kneib,J.-P.,Kuijken,K.,2001,ApJ,560,L119Hu,E.,et al.2002a,ApJ,568,L75Loeb,A.&Barkana,R.,2001,ARA&A,39,19Press,W.H.&Schechter,P.,1974,ApJ,187,425Santos,M.R.,Ellis,R.,Kneib,J.-P.,Richard,J.,Kuijken,K.,ApJ submittedSchaerer,D.2002,A&A,382,28Schaerer,D.2003,A&A,397,527Schaerer,D.&Pello R.,2001,astroph/0107274。