摘要:

I review recent observational and theoretical progress in our understanding of the cosmic evolution of luminous sources. Largely due to a combination of deepHSTimaging, Keck spectroscopy, andCOBEfar-IR background measurements, new constraints have emerged on the emission history of the galaxy population as a whole. Barring large systematic effects, the global ultraviolet, optical, near- and far-IR photometric properties of galaxies as a function of cosmic time cannot be reproduced by a simple stellar evolution model defined by a constant (comoving) star-formation density and a universal (Salpeter) IMF, and require instead a substantial increase in the stellar birthrate with lookback time. While the bulk of the stars present today appears to have formed relatively recently, the existence of a decline in the star-formation density abovez≈2remains uncertain. The history of the transition from the cosmic ‘dark age’ to a ionized universe populated with luminous sources can constrain the star formation activity at high redshifts. If stellar sources are responsible for photoionizing the intergalactic medium atz≈5,the rate of star formation at this epoch must be comparable or greater than the one inferred from optical observations of galaxies atz≈3.A population of dusty, Type II AGNs atz≲2could make a significant contribution to the FIR background if the accretion efficiency is ∼10&percent;. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58615

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We review published deep surveys in the submillimeter (sub-mm) regime from the new Sub-millimetre Common User Bolometer Array (SCUBA, [1]) on the 15-m James Clerk Maxwell Telescope (JCMT), Mauna Kea, Hawaii. Summarising the number counts of faint sub-mm sources determined from the different surveys we show that the deepest counts from our completed SCUBA Lens Survey, down to 0.5 mJy at 850 &mgr;m, fully account for the far-infrared background (FIRB) detected byCOBE. We conclude that a population of distant, dust-enshrouded ultraluminous infrared galaxies dominate the FIRB emission around 1 mm. We go on to discuss the nature of this population, starting with the identification of their optical counterparts, where we highlight the important role of deep VLA radio observations in this process. Taking advantage of the extensive archivalHubble Space Telescope (HST)observations of our fields, we then investigate the morphological nature of the sub-mm galaxy population and show that a large fraction exhibit disturbed or interacting morphologies. By employing existing broadband photometry, we derive crude redshift limits for a complete sample of faint sub-mm galaxies indicating that the majority lie atz<5,with at most 20&percent; at higher redshifts. We compare these limits to the initial spectroscopic results from various sub-mm samples. Finally we discuss the nature of the sub-mm population, its relationship to other classes of high-redshift galaxies and its future role in our understanding of the formation of massive galaxies. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58616

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Starbursts are an important component of the present-day universe, being the site of ∼25&percent; of the high-mass star-formation. They also serve as local analogs of the processes that were important in the origin and early evolution of galaxies and in the heating and chemical enrichment of the inter-galactic medium. In this contribution I review starbursts from this cosmological perspective, stressing observations at ultraviolet, infrared, and X-ray wavelengths. These data show that: 1) Local starbursts are quite similar in their UV photometric and structural properties to the UV-selected ‘Lyman-break’ galaxies at high-redshift 2) Dust dramatically affects our view of starbursts 3) More massive galaxies host more metal-rich starbursts, which are in turn more heavily extincted by dust 4) More luminous starbursts are more heavily extincted by dust 5) The strong UV interstellar absorption lines directly trace outflows of metal-rich gas, and 6) X-ray observations show that these ‘superwinds’ are strongly mass-loaded flows that carry out gas at a rate comparable to the rate of star formation at inferred velocities that are close to the escape velocity from a massive galaxy. These results suggest that the Lyman-break galaxies are typically significantly reddened and extincted by dust (average factor of 3 to 10 in the UV), may have moderately high metallicities (0.1 to 1 times solar?), are probably building galaxies with stellar surface-mass-densities similar to present-day bulges and ellipticals, and may be suffering substantial losses of metal-enriched gas that can ‘pollute’ the inter-galactic medium. The sub-mm sources detected at high-z are most likely the high-luminosity tail of the Lyman-break population, and probably represent the most metal-rich (dustiest) starbursts occurring in the most massive halos. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58617

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Understanding the nature and future evolution of star-forming galaxies found at2<z<5requires a thorough knowledge of the star formation process locally. The KPNO International Spectroscopic Survey (KISS) is a wide-field survey for extragalactic emission-line objects being carried out with the Burrell Schmidt at Kitt Peak. We have discovered approximately 1100 emission-line galaxies (ELGs) in a survey area of 68 sq. degrees (16.6 galaxies per square degree). These ELGs were identified via their H&agr; flux and have been used to measure the star formation rate (SFR) density of the local universe. We find a SFR density approximately equal to that found by Gallego &etal; (1995). We note, however, that our survey is incomplete for galaxies withEW(H&agr;)<25&hthinsp;Åimplying that thetotallocal SFR density is higher than this value. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58618

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

It is now possible to study the chemical properties of distant galaxies through emission line diagnostics which have long been used in local HIIregions. Initial results from a sample of compact, narrow emission line galaxies atz=0.2toz=0.5show a range of metallicities from metal-poor like the SMC to super solar. The oxygen abundances correlate strongly with optical luminosity just like local galaxies. This suggests that the chemical production and retention in individual galaxies is determined predominantly by local characteristics, such as the integrated star formation activity and the depth of the gravitational potential rather than the cosmic star formation history. The ratios of specific elements like nitrogen-to-oxygen can constrain the evolutionary descendants of hi-z galaxies. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58649

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Faint radio sources provide important information about global star formation history. We make use of the correlation between radio and far infrared (FIR) flux to study the faint star forming galaxies producing the FIR and radio extragalactic background emission. Combining this with the typical radio spectral indices of these sources and their number counts, we estimate their mean redshift to be roughly between 1 and 2. In a second calculation, we use a simple model of the redshift distribution of faint radio sources, in combination with the number count information, to calculate the peak star formation rate density, which we can do without knowledge of the luminosity function. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58619

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Determination of the epoch dependent star-formation rate of field galaxies is one of the principal goals of modern observational cosmology. Deep radio surveys, sensitive to starbursts out toz∼1–2,may hold the key to understanding the evolution of the starburst phenomenon unhindered by the effects of dust. Using deep, high resolution radio observations of the Hubble Deep Field, we show that the&mgr;Jyradio emission from field galaxies atz∼0.4–1is primarily starburst in origin. In addition, we have discovered a population of optically faint, possibly obscured systems that are candidate high-zprotogalaxies. At least one of these radio sources is identified with a sub-mm detection. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58650

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Foreground emission and scattered light from interplanetary dust (IPD) particles and emission from Galactic stellar sources are the greatest obstacles for determining the cosmic infrared background (CIB) from diffuse sky measurements in the ∼1 to 5 &mgr;m range. We describe a new method for deriving the CIB at near infrared wavelengths which reduces the uncertainties associated with the removal of the Galactic stellar emission component from the sky maps. The method produces positive residuals at 3.5 and 4.9 &mgr;m, of which only the 3.5 &mgr;m residual is nearly isotropic. We consider our result as a tentative detection of the CIB at this wavelength. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58621

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

We detail a technique for estimating the UV extinction and luminosity of UV selected galaxies using UV quantities alone. The technique is based on a tight correlation between the ratios of far infrared (FIR) to UV flux ratios and UV color for a sample of local starbursts. A simple empirical fit to this correlation can be used to estimate UV extinction as a function of color. This method is applied to a sample of Lyman-break systems selected from the HDF and havingz≈3.The resultant UV emissivity is at least nine times higher than the original Madau &etal; [1] estimate. This technique can be readily applied to other rest-frame UV surveys. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58622

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

In its parallel pointings, NICMOS has given us a unique window on the evolving Universe. We have analyzed the deep parallel NICMOS grism observations, covering more than 60 square arcminutes and down to continuumH1.6=22in the deepest fields. With this slitless grism spectroscopy, NICMOS reveals 33 new line-emitting galaxies. In most cases, the single emission line is likely to be H&agr; at0.7<z<1.9,and their volume density is comparable to that of the brighter galaxies selected by the Lyman break method. Our first Keck LRIS spectrum of one of these galaxies confirms this identification. The inferred star formation rates for the emission-line galaxies are 2–480M./year. We present the details of the grism survey and our analysis so far. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.58652

出版商:AIP    

年代:1999

数据来源: AIP