Differential Evolution of Lyman Break Galaxies from $z$=5 to 3

Large Equivalent width Lyman-alpha line emission at z=4.5: young galaxies in a young universe

The Large Area Lyman Alpha survey has found ~ 150 Lyman-alpha emitters at z=4.5. While stellar models predict a maximum Lyman-alpha equivalent width (EW) of 240 angstrom, 60% of the Lyman-alpha emitters have EWs exceeding this value. We attempt to model the observed EW distribution by combining stellar population models with an extrapolation of Lyman break galaxy luminosity function at z=4, incorporating observational selection effects and Malmquist bias. To reproduce the high EWs seen in the sample we need to postulate a stellar initial mass function (IMF) with extreme slope alpha = 0.5 (inst…

2001-11-06astro-ph

Lyman-alpha emission galaxies at a redshift of z = 5.7 in the FORS Deep Field

We present the results of a search for Lyman-alpha emission galaxies at z~ 5.7 in the FORS Deep Field. The objective of this study is to improve the faint end of the luminosity function of high-redshift Lyman-alpha emitting galaxies and to derive properties of intrinsically faint Lyman-alpha emission galaxies in the young universe. Using FORS2 at the ESO VLT and a set of special interference filters, we identified candidates for high-redshift Lyman-alpha galaxies. We then used FORS2 in spectroscopic mode to verify the identifications and to study their spectral properties. The narrow-band phot…

2006-04-12astro-ph

Lyman Continuum Extinction by Dust in H {\sc ii} Regions of Galaxies

We examine Lyman continuum extinction (LCE) in H II regions by comparing infrared fluxes of 49 H II regions in the Galaxy, M31, M33, and the LMC with estimated production rates of Lyman continuum photons. A typical fraction of Lyman continuum photons that contribute to hydrogen ionization in the H II regions of three spiral galaxies is $\la$ 50 %. The fraction may become smaller as the metallicity (or dust-to-gas ratio) increases. We examine the LCE effect on estimated star formation rates (SFR) of galaxies. The correction factor for the Galactic dust-to-gas ratio is 2-5.

2001-06-28astro-ph

Searches for galaxies at z > 4 through Lyman-limit imaging

We present preliminary results of a search for galaxies at z>4 through Lyman-limit imaging of the fields of known high-redshift radio-galaxies. Objects were selected by means of their broad-band colours, and spectroscopy of candidate objects in one of the fields has been performed through multi-slit spectroscopy at the 4.2m William Herschel Telescope. These spectra show some of the first z>4 galaxies to be identified using the Lyman break technique.

1997-10-22astro-ph

Evolution of Star-forming Galaxies seen from Lyman Break Galaxies at $z\sim5$

Properties of Lyman Break Galaxies at $z\sim5$ are presented and are compared with those at $z\sim 2-3$ LBGs to see evolution of LBGs from $z\sim5$ to $z \sim3-2$. The LBGs at $z\sim5$ are tend to have smaller stellar masses, but they may show large star formation rates and specific star formation rates.

2008-07-01astro-ph

Are high-redshift DLA galxies Lyman-break galaxies?

We use deep HST STIS and NICMOS images of three spectroscopically confirmed galaxy counterparts of high-redshift damped Ly-alpha (DLA) absorbers (one of which is a new discovery) to test the hypothesis that high-redshift DLA galaxies are Lyman-break galaxies. If this hypothesis is correct the emission properties of DLA galaxies must lie within the range of emission properties measured for Lyman-break galaxies of similar absolute magnitude. This will be true regardless of selection biases in the sample of detected DLA galaxies. We test this prediction using several emission properties: half-lig…

2002-03-21astro-ph

The Expected Detection of Dust Emission from High-Redshift Lyman Alpha Galaxies

Recent results have shown that a substantial fraction of high-redshift Lyman alpha galaxies contain considerable amounts of dust. This implies that Lyman alpha galaxies are not primordial, as has been thought in the past. However, this dust has not been directly detected in emission; rather it has been inferred based on extinction estimates from rest-frame ultraviolet (UV) and optical observations. This can be tricky, as both dust and old stars redden galactic spectra at the wavelengths used to infer dust. Measuring dust emission directly from these galaxies is thus a more accurate way to esti…

2008-11-17astro-ph

Lyman alpha Emission from High-Redshift Galaxies

We summarise the results of a deep search for Lyman alpha emission from star-forming regions associated with damped Lyman alpha absorption systems and conclude that the Lyman alpha luminosity of high redshift galaxies is generally less than 10^(42) erg/s . We also present a newly discovered case, in the field of the QSO Q2059-360, where the emission is unusually strong, possibly because the damped system is close in redshift to the QSO.

1995-02-16astro-ph

The Lyman continuum radiation escaping from galaxies

The H-alpha luminosity density of galaxies is used to calculate the local diffuse radiation field at the Lyman limit as resulting from star formation in the universe. The fraction of Lyman continuum radiation leaking out from galaxies through their neutral hydrogen is the most uncertain parameter of the calculation. A comparison of the diffuse radiation predicted from galaxies with that measured from all sources of ionization shows that the average Lyman continuum escape fraction should be lower than 1%. This number is lower than the upper limits reported so far in a few objects. It is also sh…

1997-04-15astro-ph

Lyman Break Galaxies and Luminous IR Galaxies at z ~ 1

We use deep GALEX images of CDFS in UV to define the first large sample of 420 Lyman Break Galaxies at z~1. We use a PSF fitting to estimate UV magnitudes on these deep crowded images. Deep Spitzer IRAC and MIPS provide the first detection of a large sample of Lyman Break Galaxies in the mid- to far-infrared range. We are therefore able to study and compare the UV and TIR emission of Lyman Break Galaxies. We find that about 15% of the LBG sample are strong emitters at 24 microns (Red LBGs). Most of them are Luminous IR Galaxies (LIRGs) while the rest (Blue LBGs) are undetected at the 83 microJ…

2007-01-11astro-ph

Abundances of Heavy Elements and CO Molecules in High Redshift Damped Lyman-alpha Galaxies

Damped Lyman-alpha systems seen in spectra of background quasars are generally thought to represent high redshift counterparts of present-day galaxies. We summarize observations of heavy element abundances in damped Lyman-alpha systems. The results of a systematic search for CO and C II* absorption in 17 damped Lyman-alpha systems are also presented using observations obtained with the 10m Keck telescopes. The latter provides a useful constraint on the expected strength of [C II] 158 micron emission from damped Lyman-alpha galaxies. It is hoped that these results will be useful for planning fu…

1997-11-25astro-ph

The Chemical Evolution of Damped Lyman Alpha Galaxies

Measurements of element abundances in damped Lyman alpha systems are providing new means to investigate the chemical evolution of galaxies, particularly at early times. We review progress in this area, concentrating on recent efforts to extend the range of existing surveys to both higher and lower redshifts.

1995-02-08astro-ph

Spectroscopic Confirmation of Faint Lyman Break Galaxies at Redshifts Four and Five in the Hubble Ultra Deep Field

We present the faintest spectroscopically confirmed sample of redshift four and five Lyman break galaxies to date. The sample is based on slitless grism spectra of the Hubble Ultra Deep Field region from the GRAPES (Grism ACS Program for Extragalactic Science) and PEARS (Probing Evolution and Reionization Spectroscopically) projects, using the G800L grism on the HST Advanced Camera for Surveys. We report here confirmations of 39 galaxies, pre-selected as candidate Lyman break galaxies using photometric selection criteria. We compare a "traditional" V-dropout selection to a more liberal one (wi…

2008-05-07astro-ph

Abundances at High Redshifts: the Chemical Enrichment History of Damped Lyman-alpha Galaxies

Damped Lyman-alpha absorption systems found in the spectra of high redshift quasars are believed to trace the interstellar gas in high redshift galaxies. In this paper, we study the elemental abundances of C, N, O, Al, Si, S, Cr, Mn, Fe, Ni, and Zn in a sample of 14 damped Lyman-alpha systems using high quality echelle spectra of quasars obtained with the 10m Keck telescope. These abundances are combined with similar measurements in the literature in order to investigate the chemical evolution of damped Lyman-alpha galaxies in the redshift range 0.7<z<4.4. Among the things investigated are: th…

1996-06-07astro-ph

Lyman alpha emission in high-redshift galaxies

A significant fraction of the high-redshift galaxies show strong Lyman emission lines. For redshifts z>5, most known galaxies belong to this class. However, so far not much is known about the physical structure and nature of these objects. Our aim is to analyse the Lyman alpha emission in a sample of high-redshift UV-continuum selected galaxies and to derive the physical conditions that determine the Lyman alpha profile and the line strength. VLT/FORS spectra with a resolution of R ~ 2000 of 16 galaxies in the redshift range of z = 2.7 to 5 are presented. The observed Lyman alpha profiles are …

2007-02-15astro-ph

Luminosity Dependent Evolution of Lyman Break Galaxies from redshift 5 to 3

In this contribution we briefly describe our recent results on the properties of Lyman break galaxies at z~5 obtained from deep and wide blank field surveys using Subaru telescope, and through the comparison with samples at lower redshift ranges we discuss the evolution of star-forming galaxies in the early universe.

2006-11-17astro-ph

First Investigation of the Clustering Environment of Damped Lyman Alpha Absorbers at z=4

We report the first observations of the clustering environment of damped Lyman alpha absorption systems at z=4. Color selection and photometric redshifts were used to select 44 candidate Lyman-break galaxies brighter than I_AB=25.5 from deep BRI images of the 35 sq. arcmin field containing the quasar BR 0951-04. Multislit spectroscopy of 35 candidate galaxies was performed and 8 of these candidates have been confirmed as z>3.5 Lyman-break galaxies. With only BRI photometry, the photometric redshifts are quite accurate for the spectroscopically confirmed galaxies but have a high rate of misclas…

2001-07-10astro-ph

Large Area Lyman Alpha survey: finding young galaxies at z=4.5

Strong Lyman-alpha emission is a signpost of young stars and the absence of dust and thus indicates young galaxies. To find such a population of young galaxies at z=4.5 we started the Large Area Lyman Alpha survey (LALA). This survey achieves an unprecedented combination of volume and sensitivity by using narrow-band filters on a large format (36x36 square-arcminutes) camera on the 4 meter telescope at KPNO. The volume density and star-formation contribution of the Lyman-alpha emitters at z=4.5 is comparable to that of Lyman break galaxies. With many candidates and a few spectroscopic confirma…

2001-02-08astro-ph

Damped Lyman-Alpha Galaxies

Some results from an imaging program to identify low-redshift (0.09<z<1.63) damped Lyman-alpha (DLA) galaxies are presented. The standard paradigm that was widely accepted a decade ago, that DLA galaxies are the progenitors of luminous disk galaxies, is now being seriously challenged. The indisputable conclusion from imaging studies at low redshift is that the morphological types of DLA galaxies are mixed and that they span a range in luminosities and surface brightnesses.

2000-10-31astro-ph

Measurement of the Spatial Cross-Correlation Function of Damped Lyman Alpha Systems and Lyman Break Galaxies

We present the first spectroscopic measurement of the spatial cross-correlation function between damped Lyman alpha systems (DLAs) and Lyman break galaxies (LBGs). We obtained deep u'BVRI images of nine QSO fields with 11 known z ~ 3 DLAs and spectroscopically confirmed 211 R < 25.5 photometrically selected z > 2 LBGs. We find strong evidence for an overdensity of LBGs near DLAs versus random, the results of which are similar to that of LBGs near other LBGs. A maximum likelihood cross-correlation analysis found the best fit correlation length value of r_0 = 2.9^(+1.4)_(-1.5) h^(-1)Mpc using a …

2005-11-17astro-ph

Lyman alpha emission from local starburst galaxies and high-z objects

We review the history and the current status of the understanding of the processes that regulate Lyman alpha emission from star-forming galaxies. We present some of the most recent results of our study to image local starburst galaxies in the Lyman alpha emission line using the Advanced Camera for Surveys on the Hubble Space Telescope. Particular attention is dedicated to our study of the low-metallicity, dust-poor Blue Compact Galaxy ESO338-IG04. We discuss some of our local observational results with reference to the interpretation of results of high-redshift Lyman alpha surveys and recent s…

2005-07-15astro-ph

The Lyman-alpha emission in local Star-Forming Galaxies: Scenario and Connection with Primeval Galaxies

We review the Lyan alpha emission in local star-forming galaxies. In most cases as already shown by the IUE, the emission is absent or much weaker than expected. This occurs because Lyman alpha photons can be resonantly scattered by the neutral gas and destroyed by even very low amounts of dust. However new Hubble Space Telescope observations (HST) indicate that other factors such as the velocity structure of the gas play a crucial role. Gas flows are likely to occur as powered by the kinetic energy released via stellar winds and supernova. We propose a scenario based on the hydrodynamics of s…

1998-09-08astro-ph

Discovery of z=0.0912 and z=0.2212 Damped Lyman-alpha Absorption Line Systems Toward the Quasar OI 363: Limits on the Nature of Damped Lyman-alpha Galaxies

The discovery of a z_abs = 0.0912 damped Lyman-alpha absorption-line system in the HST-FOS ultraviolet spectrum of the quasar OI 363 (0738+313) is reported. This is the lowest redshift quasar damped Lyman-alpha system known. Its neutral hydrogen column density is N(HI) = 1.5(+/- 0.2) E21 atoms/cm^2, which easily exceeds the classical criterion for damped Lyman-alpha of N(HI) greater than or equal to 2E20 atoms/cm^2. Remarkably, a z_abs = 0.2212 damped system with N(HI) = 7.9(+/- 1.4) E20 atoms/cm^2 has also been discovered in the same spectrum. In the past, the standard paradigm for damped Lym…

1998-05-07astro-ph

Lyman Alpha Emitters at Redshift z=5.7

Lyman alpha galaxies at high redshifts offer a powerful probe of both the formation of galaxies and the reionization of the intergalactic medium. Lyman alpha line emission is an efficient tool for identifying young galaxies at high redshift, because it is strong in systems with young stars and little or no dust-- properties expected in galaxies undergoing their first burst of star-formation. Lyman alpha galaxies also provide a robust test of the reionization epoch that is independent of Gunn-Peterson trough observations in quasar spectra and is better able to distinguish line center optical de…

2001-11-06astro-ph

Gas-Rich Local Dwarf Star-Forming Galaxies and their connection with the Distant Universe

I discuss the properties of gas-rich forming galaxies. I particularly emphasize the latest results on Lyman alpha emission that are relevant to the search of distant young galaxies. The interdependance of the Lyman alpha escape with the properties of the ISM in starburst galaxies is outlined. A new model from G. Tenorio-Tagle and his collaborators explaining Lyman alpha profiles in starburst galaxies from the hydrodynamics of superbubbles powered by massive stars is presented. I stress again that since Lyman alpha is primarely a diagnostic of the ISM, it is mandatory to understand how the ISM …

1998-12-17astro-ph

Correlation of Low z Lyman-alpha Absorbers with HI-selected Galaxies

In this work, observational evidence for the connection between low column density Lyman-alpha absorbers and large-scale structure traced by gas-rich galaxies is investigated. The HI Parkes All Sky Survey (HIPASS) galaxy catalogue is cross-correlated with known low redshift, low column density Lyman-alpha absorbers from the literature. The absorber-galaxy cross-correlation function shows that on scales from 1 to 10 h^-1 Mpc, absorbers are imbedded in halos with masses similar to that of galaxy groups. This statistical evidence suggests that galaxy groups could be the dominant environment of lo…

2005-04-22astro-ph

Spectroscopy of z>3 Lyman-limit Galaxies

We discuss the spectral character of Lyman-limit-selected, star-forming galaxies at z>3. The rest-frame UV spectra of these faint galaxies may show Ly-alpha in either absorption or emission, probably depending upon their local ISM content and geometry. Other UV interstellar resonance absorption lines show considerable variation in strength, likely related to differences in the galactic metal abundances. We present initial results on B-drop galaxies, generally at z~4. Our low-resolution spectrograms show no measurable flux below the redshifted Lyman limit (912 Angstroms). Thus, it is likely tha…

1998-02-11astro-ph

The N/Si Abundance Ratio in Fifteen Damped Lyman-alpha Galaxies: Implications for the Origin of Nitrogen

Galactic chemical evolution model calculations indicate that there should be considerable scatter in the observed N/O ratios at a fixed metallicity (O/H) for galaxies with very low metallicities due to the delayed release of primary N from intermediate mass stars relative to that of O from short-lived massive stars. Moreover, the scatter should increase progressively toward decreasing metallicity. Such effects have not been convincingly demonstrated by observations of H II regions in nearby metal-poor galaxies, raising doubts about the time-delay model of primary N production. Pettini et al an…

1997-10-28astro-ph

A Counts-in-Cells Analysis of Lyman-break Galaxies at z~3

We have measured the counts-in-cells fluctuations of 268 Lyman-break galaxies with spectroscopic redshifts in six 9 arcmin by 9 arcmin fields at z~3. The variance of galaxy counts in cubes of comoving side length 7.7, 11.9, 11.4 h^{-1} Mpc is σ_{gal}^2 ~ 1.3\pm0.4 for Ω_M=1, 0.2 open, 0.3 flat, implying a bias on these scales of σ_{gal} / σ_{mass} = 6.0\pm1.1, 1.9\pm0.4, 4.0\pm0.7. The bias and abundance of Lyman-break galaxies are surprisingly consistent with a simple model of structure formation which assumes only that galaxies form within dark matter halos, that Lyman-break galaxies' rest-U…

1998-04-23astro-ph

The Compared Number Density of High-Redshift Galaxies and Lyman αClouds

We use our catalog of photometric redshifts in the Hubble Deep Field (HDF) to estimate the Luminosity Function (LF) of galaxies up to z=2. Using the obtained LF and a relationship between luminosity and halo size, we calculate the expected density of galactic halo crossings for any arbitrary line of sight. This density is then compared with the known one of Lyman αlines, showing that the observed density of galaxies is enough to account for the observed absorption lines.

1997-09-15astro-ph

Undetected Sources Allow Transmission of the Lyman-alpha Line From Galaxies Prior to Reionization

The discovery of Lyman-alpha emission from galaxies at redshifts beyond z~6.5 should not be naively interpreted as implying that the intergalactic medium (IGM) had been reionized at higher redsifts. We show that a cluster of faint undetected sources around each observed galaxy generates an HII region sufficiently large to allow transmission of the galaxy's Lyman-alpha line prior to reionization. We also show that quasars may contribute a significant fraction of the ionizing photons to HII regions around galaxies with a velocity dispersion larger than ~100km/s. These contributing quasars are no…

2004-07-09astro-ph

Requirements for Investigating the Connection Between Lyman Alpha Absorption Clouds and the Large-Scale Distribution of Galaxies

We model the requirements on observational data that would allow an accurate determination of the degree of association between Lyman alpha absorbers and peaks in the redshift distribution of galaxies (large-scale structures like clusters of galaxies). We compare simulated distributions of low-redshift Lyman alpha absorption systems, constrained to be consistent with the distribution observed with HST, with the large-scale distribution of galaxies determined from pencil-beam redshift surveys. We estimate the amount of observational data required from catalogues of Lyman alpha absorbers and gal…

1995-08-16astro-ph

Deficiency of large equivalent width Lyman-alpha emission in luminous Lyman break galaxies at z~5-6?

We report a deficiency of luminous Lyman break galaxies (LBGs) with a large rest-frame equivalent width (EW_rest) of Lyman-alpha emission at z~5-6. Combining our spectroscopic sample of LBGs at z~5 and those from the literature, we found that luminous LBGs at z~5-6 generally show weak Lyman-alpha emissions, while faint LBGs show a wide range of Lyman-alpha EW_rest and tend to have strong (EW_rest >20A) Lyman-alpha emissions; i.e., there is a deficiency of strong Lyman-alpha emission in luminous LBGs. There seems to be a threshold UV luminosity for the deficiency; it is M_1400 = -21.5 \~ -21.0 …

2006-06-28astro-ph

Deep Observations of Lyman Break Galaxies

We summarise the main results of recent work on the Lyman break galaxy population which takes advantage of newly commissioned instrumentation on the VLT and Keck telescopes to push the detection of these objects to new wavelengths and more sensitive limits. We focus in particular on near-infrared observations targeted at detecting emission lines of [O II], [O III], and H-beta and on the first tentative detection of Lyman continuum emission from star forming galaxies at z = 3.

2001-01-16astro-ph

Lyman Break Galaxies at z~3 and Beyond

We report on the status of large surveys of photometrically selected star forming galaxies at z~3 and z~4, with particular emphasis on both the advantages and the limitations of selecting objects using the ``Lyman break'' technique. Current results on the luminosity functions, luminosity densities, color distribution, star formation rates, clustering properties, and the differential evolution of the population as a function of redshift are summarized.

1998-12-09astro-ph

Properties of Low-Redshift Damped Lyman Alpha Galaxies

Images of five QSO fields containing six damped Lyman alpha (DLA) systems at redshifts 0.09<z<0.53 are presented. Identifications for the DLA galaxies giving rise to the DLA systems are made. The observed and modeled characteristics of the DLA galaxies are discussed. The DLA galaxies have impact parameters ranging from < 4 kpc to \approx 34 kpc and luminosities in the range \approx 0.03L* to \approx 1.3L*. Their morphologies include amorphous low surface brightness systems, a probable dwarf spiral, and luminous spirals.

2001-08-08astro-ph

An HST Search for Lyman Continuum Emission From Galaxies at z=1.1--1.4

If enough of their Lyman limit continuum escapes, star-forming galaxies could be significant contributors to the cosmic background of ionizing photons. To investigate this possibility, we obtained the first deep imaging in the far ultraviolet of eleven bright blue galaxies at intermediate redshift (z=1.1--1.4). NO Lyman continuum emission was detected. Sensitive, model-independent, upper limits of typically 2 x 10**-19 erg/sec/cm2/Ang were obtained for the ionizing flux escaping from these normal galaxies. This corresponds to lower limits on the observed ratio of 1500 to 700Ang flux of 150 up …

2003-10-08astro-ph

A Low Upper Limit to the Lyman Continuum Emission of two galaxies at z 3

Long exposure, long-slit spectra have been obtained in the UV/optical bands for two galaxies at z=2.96 and z=3.32 to investigate the fraction of ionizing UV photons escaping from high redshifts galaxies. The two targets are among the brightest galaxies discovered by Steidel and collaborators and they have different properties in terms of Lyman-alpha emission and dust reddening. No significant Lyman continuum emission has been detected. The noise level in the spectra implies an upper limit of f_{rel,esc}\equiv 3 f(900)/f(1500)< 16% for the relative escape fraction of ionizing photons, after cor…

2002-02-15astro-ph

Comparing Galaxies and Lyman Alpha Absorbers at Low Redshift

A scenario is explored in which Lyman alpha absorbers at low redshift arise from lines of sight through extended galaxy disks, including those of dwarf and low surface brightness galaxies. A population of galaxies is simulated based upon observed distributions of galaxy properties, and the gas disks are modeled using pressure and gravity confinement. Some parameter values are ruled out by comparing simulation results with the observed galaxy luminosity function, and constraints may be made on the absorbing cross sections of galaxies. Simulation results indicate that it is difficult to match ab…

1997-09-26astro-ph

A Monte Carlo simulation of the intergalactic absorption and the detectability of the Lyman continuum from distant galaxies

We have made a Monte Carlo simulation of the intergalactic absorption in order to model the Lyman continuum absorption, which is required to estimate the escape fraction of the Lyman continuum from distant galaxies. To input into the simulation, we derive an empirical distribution function of the intergalactic absorbers which reproduces recent observational statistics of the Lyman $α$ forest, Lyman limit systems (LLSs), and damped Lyman $α$ systems (DLAs) simultaneously. In particular, we assume a common functional form of the number evolution along the redshift for all types of absorbers. The…

2008-04-18astro-ph

The Environmental Impact of Lyman-break Galaxies

We perform cosmological simulations of galaxies forming at z=3 using the hydrodynamics grid code, Enzo. By selecting the largest galaxies in the volume to correspond to Lyman-break galaxies, we construct observational spectra of the HI flux distribution around these objects, as well as column densities of CIV and OVI throughout a refined region. We successfully reproduce the most recent observations of the mean HI flux in the close vicinity of Lyman-break galaxies but see no evidence for the proximity effect in earlier observations. While our galaxies do return metals to the IGM, their quantit…

2006-04-11astro-ph

Lyman Alpha Galaxies: Primitive, Dusty or Evolved Galaxies?

We present stellar population modeling results for 10 newly discovered Lyman alpha emitting galaxies (LAEs), as well as four previously known LAEs at z ~ 4.5 in the Chandra Deep Field - South. We fit stellar population models to these objects in order to learn specifically if there exists more than one class of LAE. Past observational and theoretical evidence has shown that while many LAEs appear to be young, they may be much older, with Lyman alpha EWs enhanced due to resonant scattering of Lyman alpha photons in a clumpy interstellar medium (ISM). Our results show a large range of stellar po…

2008-10-02astro-ph

Lyman Break Galaxies and the Reionization of the Intergalactic Medium

Near-infrared observations of Lyman-break galaxies at redshifts z~3 are beginning to provide constraints on ages, star-formation histories, dust content, metallicities, and stellar masses. At present, uncertainties of more than an order of magnitude are typical for many of these parameters. It is nonetheless interesting to ask what the stellar-population models imply for the existence and luminosities of Lyman-break galaxies at higher redshift. To this end we examine the inferred star-formation rates in two well-studied samples of galaxies as a function of redshift out to z = 10 for various be…

2002-04-11astro-ph

Lyman break galaxies as young spheroids

We investigate the nature of Lyman break galaxies (LBGs) using a chemodynamical model for evolution of galaxies. Our models predict an early (the first Gyr) stage of intense star formation in the evolution of massive spheroids which could be identified to the LBGs, observed at redshift $\sim 3$ with strong ongoing star formation. In particular, we are successful in reproducing the properties of the LBG DSF 2237+116 C2 with a model describing a young $\sim L^*$ spheroid. The comparison of the predictions of our models with the observations gives support to the scenario in which LBGs are the pro…

1999-01-22astro-ph

Building the bridge between Damped Ly-alpha Absorbers and Lyman Break galaxies

In 2000, we started the program ``Building the Bridge between Damped Ly-alpha Absorbers and Lyman-Break Galaxies: Ly-alpha Selection of Galaxies'' at the European Southern Observatory's Very Large Telescope. This project is an attempt to use Ly-alpha selection of high-z galaxies to bridge the gap between absorption- and emission-selected galaxies by creating a large database of z=3 galaxies belonging to the abundant population of faint (R>25.5) galaxies probed by the Damped Ly-alpha Absorbers (DLAs). Here we present the first results of our program, namely the results from a deep Ly-alpha stud…

2002-06-26astro-ph

On the Spatial Correlations of Lyman Break Galaxies

Motivated by the observed discrepancy between the strong spatial correlations of Lyman break galaxies (LBGs) and their velocity dispersions, we consider a theoretical model in which these starbursting galaxies are associated with dark matter halos that experience appreciable infall of material. We show using numerical simulation that selecting halos that substantially increase in mass within a fixed time interval introduces a ``temporal bias'' which boosts their clustering above that of the underlying population. If time intervals consistent with the observed LBGs star formation rates of 50 so…

2003-05-19astro-ph

Pushing Back Studies of Galaxies Toward the Dark Ages: High-Redshift Lyman alpha Emission-Line Galaxies in the Field

Lyman alpha emission presents a means of identifying very high redshift galaxies, provided such objects can be reliably distinguished from foreground emission-line galaxies. Here we report on a program of imaging and spectroscopic studies being conducted with the Keck telescope, in concert with additional efforts from the ground and with HST, to study such high-redshift objects over the range from z=3 to 7. The first deep narrow-band imaging studies with Keck are used to show that strong Lyman alpha emitters, such as have been seen in high-redshift quasar fields at z>4.5, can be found in the f…

1998-01-17astro-ph

Damped Lyman alpha systems and disk galaxies: number density, column density distribution and gas density

We present a comparison between the observed properties of damped Lyman alpha systems (DLAs) and the predictions of simple models for the evolution of present day disk galaxies, including both low and high surface brightness galaxies. We focus in particular on the number density, column density distribution and gas density of DLAs, which have now been measured in relatively large samples of absorbers. From the comparison we estimate the contribution of present day disk galaxies to the population of DLAs, and how it varies with redshift. Based on the differences between the models and the obser…

2002-08-26astro-ph

Lyman-alpha absorption : links between CSS quasars and high-redshift radio galaxies

Spectroscopy of high-redshift compact steep-spectrum (CSS) quasars shows a high incidence of Ly-alpha absorption close to the quasar redshift. Associated absorption systems like these are rare in other types of radio sources, with the notable exception of high-redshift radio galaxies (HZRGs). CSS quasars and HZRGs share many properties; the hypothesis that they are intrinsically similar objects is presented and discussed.

1997-12-11astro-ph

A Luminosity Function of Lyman Alpha Emitting Galaxies at Redshift 4.5

We present a catalog of 59 z=4.5 Lyman alpha emitting galaxies spectroscopically confirmed in a campaign of Keck/DEIMOS follow-up observations to candidates selected in the Large Area Lyman Alpha (LALA) narrow-band imaging survey. We targeted 97 candidates for spectroscopic follow-up; by accounting for the variety of conditions under which we performed spectroscopy, we estimate a selection reliability of about 76%. Together with our previous sample of Keck/LRIS confirmations, the 59 sources confirmed herein bring the total catalog to 73 spectroscopically confirmed z=4.5 Lyman alpha emitting ga…

2007-07-27astro-ph

Constraints on the Unseen Galaxy Population from the Lyman-alpha Forest

Here we describe results of our attempt to determine what types of galaxies are responsible for the Lyman-alpha forest absorption systems, based on our ongoing imaging and spectroscopic survey of faint galaxies in fields of HST spectroscopic target QSOs. Our primary conclusions are that the bulk of the Lyman-alpha forest arises in more or less normal galaxies (that span the normal range of luminosity and morphology) and that any ``unseen'' low surface brightness galaxies are unlikely to contribute significantly to the luminosity density of the universe.

1998-12-15astro-ph

The Nature of Lyman Break Galaxies in Cosmological Hydrodynamic Simulations

What type of objects are being detected as $z\sim 3$ "Lyman break galaxies"? Are they predominantly the most massive galaxies at that epoch, or are many of them smaller galaxies undergoing a short-lived burst of merger-induced star formation? We attempt to address this question using high-resolution cosmological hydrodynamic simulations including star formation and feedback. Our $Λ$CDM simulation, together with Bruzual-Charlot population synthesis models, reproduces the observed number density and luminosity function of Lyman break galaxies when dust is incorporated. The inclusion of dust is c…

1999-10-12astro-ph

Lyman Break Galaxies in the NGST Era

With SIRTF and NGST in the offing, it is interesting to examine what the stellar populations of z~3 galaxies models imply for the existence and nature of Lyman-break galaxies at higher redshift. To this end, we ``turn back the clock'' on the stellar population models that have been fit to optical and infrared data of Lyman-break galaxies at z~3. The generally young ages (typically 10^8 +- 0.5 yr) of these galaxies imply that their stars were not present much beyond z=4. For smooth star-formation histories SFR(t) and Salpeter IMFs, the ionizing radiation from early star-formation in these galax…

2002-04-11astro-ph

Low Redshift Lyman Alpha absorbers and their Connection with Galaxies

We review the ongoing debate about the relationship between low redshift Lyman Alpha absorbers and luminous galaxies. In particular, we discuss the difficulty of `assigning' a particular absorber to a particular galaxy, and consider methods of circumventing this problem. We also provide a status report on an ongoing project collecting more data to address this issue, and show some results for a close together pair of QSOs providing two adjacent lines of sight through the inter-galactic medium.

2001-08-08astro-ph