摘要:

We show that most gravitational lenses lie on the passively evolving fundamental plane for early-type galaxies. For burst star formation models (1 Gyr of star formation, then quiescence) in low&OHgr;0cosmologies, the stellar populations of the lens galaxies must have formed atzf≳2.Typical lens galaxies contain modest amounts of patchy extinction, with a median differential extinction for the optical (radio) selected lenses of&Dgr;E(B−V)=0.04(0.07)&hthinsp;mag.The dust can be used to determine both extinction laws and lens redshifts. For example, thezl=0.96elliptical lens inMG0414+0534has anRV=1.7±0.1mean extinction law. Arc and ring images of the quasar and AGN source host galaxies are commonly seen in NICMOS H band observations. The hosts are typically blue,L≲L*galaxies. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58598

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

A theoretical formulation for a two-point correlation function of high-redshift objects is investigated. While all the cosmological observations are carried out on a light-cone, the null hypersurface of an observer atz=0,the clustering statistics has been properly defined only on the constant-time hypersurface. We develop the theoretical formulation for the two-point correlation function on the light-cone, and derive a simple approximate expression relevant to the discussion of clustering of high-redshift objects. As an example, we present a prediction of the two-point correlation function for the SDSS quasar catalogue. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58599

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We calculate the expected number of multiply-imaged galaxies in the Hubble Deep Field (HDF), using photometric redshift information for galaxies withmI<27that were detected in all four HDF passbands. A comparison of these expectations with the observed number of strongly lensed galaxies constrains the current value of&OHgr;m−&OHgr;&Lgr;,where&OHgr;mis the mean mass density of the universe and&OHgr;&Lgr;is the normalized cosmological constant. Based on current estimates of the HDF luminosity function and associated uncertainties in individual parameters, our 95&percent; confidence lower limit on&OHgr;m−&OHgr;&Lgr;ranges between −0.44, if there are no strongly lensed galaxies in the HDF, and −0.73, if there are two strongly lensed galaxies in the HDF. If the only lensed galaxy in the HDF is the one presently viable candidate, then, in a flat universe(&OHgr;m+&OHgr;&Lgr;=1),&OHgr;&Lgr;<0.79(95&percent; C.L.). These limits are compatible with estimates based on high-redshift supernovae and with previous limits based on gravitational lensing. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58600

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We review recent results of Sunyaev-Zel’dovich-effect (SZE) observations toward galaxy clusters. Using cm-wave receivers mounted on the OVRO and BIMA mm-wave arrays, we have obtained high signal-to-noise images of the effect for more than 25 clusters. Over 90&percent; of these clusters are scheduled to be observed withAXAFduring the first year of its observations. We present current estimates of cosmological parametersH0and&OHgr;mbased on the SZE in galaxy clusters. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58646

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Theoretical considerations and observational data support the idea that mergers were more frequent in the past. At redshiftsz=2to 5, violent interactions and mergers may be implicated by observations of Lyman-break galaxies, sub-mm starbursts, and active galactic nuclei. Most stars in cluster ellipticals probably formed at such redshifts, as did most of the halo and globular clusters of the Milky Way; these events may all be connected with mergers. But whatkindof galaxies merged at high redshifts, and are present-epoch mergers useful guides to these early collisions? I will approach these questions by describing ideas for the formation of the Milky Way, elliptical galaxies, and systems of globular clusters. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58601

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We review recent clues from deep HST images on the formation and evolution of galaxies, and the role that mergers have played in this process. First, we first review the evidence from deep ground-based and HST studies for an epoch dependent merger rate, which was higher in the past by∼(1+z)mwithm≃1.5−3out toz≲1−2.Next, we review clues from deep HST broad-band images to the role of (minor) mergers. The galaxy counts as a function of restframe type show that E/SO’s and Sabc’s are only marginally evolving, but show that Sd/Irr’s are the dominant population forB≲27&hthinsp;mag,or1≲z≲2.The scale-lengths of all galaxy types decrease steadily towards the faintest flux limits. A significant fraction of the faint blue irregulars have close companions and/or tidal features indicating merging atz≳1.5–2,implying an epoch of merger-induced star-formation forz∼1.5–2,which also coincides with the peak in the star-formation rate [44]. This suggests a Universe atz≳1.5dominated by hierarchical merging of star-forming (irregular) “sub-galactic” sized objects. We then summarize the clues that HST medium-band searches have played in finding these “sub-galactic” building blocks, as well as searches with similar techniques from the ground. Next, we review high resolution PC images, as well as other data, on the faint radio galaxy 53W002 atz=2.390,and suggest how and when merging would have taken place in this object to produce its most likely counterpart today—a giant elliptical galaxy. Last, we present recent HST/NICMOS images of microJansky radio sources without clear optical counterparts in the HDF/Flanking Fields, and suggest how the process of (early) major mergers could have resulted in a non-negligible fraction of the radio-selected star-formation rate to be optically enshrouded by dust. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58602

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Explaining the nature of the Lyman Break Galaxies (LBGs) recently discovered [1,2] at redshiftz∼3,is an exciting challenge for the paradigm of hierarchical structure formation. These galaxies are forming stars at a rate comparable to locally rare “starburst” galaxies [3], but are as luminous and numerous as local bright galaxies. In addition, the brightest LBGs have small emission line-widths [4], indicating viral masses of∼1−5×1010&hthinsp;M⊙,however LBGs exhibit strong clustering, similar to the properties expected of the most massive(∼1012M⊙)dark matter halos [5–8] at this redshift. We explore a possible solution to these apparent paradoxes: that LBGs are a population of collision-driven starburst galaxies which are abundant due to an increased collision rate at high redshift [2,9]. We use high-resolution cosmologicalN-body simulations and a hierarchical halo finder to estimate the galaxy collision rate as a function of time in a popular cosmological model (&Lgr;CDM). We find that appropriate collisions are frequent enough, and the ensuing bursts are plausibly bright enough, to account for most of the LBGs. Although many of the simulated collisions have relatively small masses(∼1010M⊙),they tend to cluster about large-mass halos. They therefore exhibit strong clustering, similar to that observed [1,11,8] and stronger than that of halos. The collision-induced starburst scenario [2,9] thus appears to explain the key observed properties of the high-zgalaxies. This picture can be further tested observationally, and distinguished from other scenarios, by more detailed studies of the evolution of the number density of LBGs with redshift and the dependence of their clustering on scale and environment. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58603

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Using an HST imaging survey, we have devised a morphological classification scheme for ULIRGs. We have used the results to uncover evidence for a multiple-merger origin for a significant fraction of the ULIRG population. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58604

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We present a new method of utilizing the color and asymmetry values for galaxies in the Hubble Deep Field to determine both their morphological features and physical parameters. By using a color-asymmetry diagram, we show that various types of star-forming galaxies (e.g. irregular versus interacting, peculiar galaxies) can be distinguished in local samples. We apply the same methods to the F814W images of the Hubble Deep Field, and show preliminary results indicating that galaxy mergers and interactions are the dominate process responsible for creating asymmetries in the HDF galaxies. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58605

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

It has been just over a decade since quasars first opened thez>4universe for detailed study. These distant beacons have cast a revealing light on the conditions present in the universe’s first billion years, on topics ranging from the formation of massive structures to the properties of intergalactic gas. This paper reviews the techniques used to discover distant quasars, the current state of the field (which is based on but a few dozen objects), and some predictions for what awaits us in the next ten years. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58606

出版商:AIP    

年代:1999

数据来源: AIP