Rest-frame UV Luminosity Function Research Articles

Dust properties of Lyman-break galaxies in cosmological simulations

Recent observations have indicated the existence of dust in high-redshift galaxies, however, the dust properties in them are still unknown. Here we present theoretical constraints on dust properties in Lyman break galaxies (LBGs) at z=3 by post-processing a cosmological smoothed particle hydrodynamics simulation with radiative transfer calculations. We calculate the dust extinction in 2800 dark matter halos using the metallicity information of individual gas particles in our simulation. We use only bright galaxies with rest-frame UV magnitude M_1700 < -20 mag, and study the dust size, dust-to-metal mass ratio, and dust composition. From the comparison of calculated color excess between B and V-band (i.e., E(B-V)) and the observations, we constrain the typical dust size, and show that the best-fitting dust grain size is ~ 0.05 micron, which is consistent with the results of theoretical dust models for Type-II supernova. Our simulation with the dust extinction effect can naturally reproduce the observed rest-frame UV luminosity function of LBGs at z=3 without assuming an ad hoc constant extinction value. In addition, in order to reproduce the observed mean E(B-V), we find that the dust-to-metal mass ratio needs to be similar to that of the local galaxies, and that the graphite dust is dominant or at least occupy half of dust mass.

THE LBT BOÖTES FIELD SURVEY. I. THE REST-FRAME ULTRAVIOLET AND NEAR-INFRARED LUMINOSITY FUNCTIONS AND CLUSTERING OF BRIGHT LYMAN BREAK GALAXIES ATZ∼ 3

We present a deep LBT/LBC U-band imaging survey (9 deg2) covering the NOAO Bootes field. A total of 14,485 Lyman Break Galaxies (LBGs) at z~3 are selected, which are used to measure the rest-frame UV luminosity function (LF). The large sample size and survey area reduce the LF uncertainties due to Poisson statistics and cosmic variance by >3 compared to previous studies. At the bright end, the LF shows excess power compared to the best-fit Schechter function, which can be attributed to the contribution of $z\sim3$ quasars. We compute the rest-frame near-infrared LF and stellar mass function (SMF) of z~3 LBGs based on the R-band and IRAC [4.5 micro m]-band flux relation. We investigate the evolution of the UV LFs and SMFs between z~7 and z~3, which supports a rising star formation history in the LBGs. We study the spatial correlation function of two bright LBG samples and estimate their average host halo mass. We find a tight relation between the host halo mass and the galaxy star formation rate (SFR),which follows the trend predicted by the baryonic accretion rate onto the halo, suggesting that the star formation in LBGs is fueled by baryonic accretion through the cosmic web. By comparing the SFRs with the total baryonic accretion rates, we find that cosmic star formation efficiency is about 5%-20% and it does not evolve significantly with redshift, halo mass, or galaxy luminosity.

Two epochs of globular cluster formation from deep field luminosity functions: implications for reionization and the Milky Way satellites

The ages of globular clusters in our own Milky Way are known with precision of about \pm 1 Gyr, hence their formation at redshifts z>~3 and their role in hierarchical cosmology and the reionization of the intergalactic medium remain relatively undetermined. Here we analyze the effect of globular cluster formation on the observed rest-frame UV luminosity functions (LFs) and UV continuum slopes of high redshift galaxies in the Hubble Ultra Deep Fields. We find that the majority of present day globular clusters have formed during two distinct epochs: at redshifts z ~ 2-3 and at redshifts z>~6. The birth of proto-GC systems produce the steep, faint-end slopes of the galaxy LFs, and because the brightness of proto-GCs fades 5 Myrs after their formation, their blue colors are in excellent agreement with observations. Our results suggest that: i) the bulk of the old globular cluster population with estimated ages >~12 Gyr (about 50% of the total population), formed in the relatively massive dwarf galaxies at redshifts z>~6; ii) proto-GC formation was an important mode of star formation in those dwarf galaxies, and likely dominated the reionization process. Another consequence of this scenario is that some of the most massive Milky Way satellites may be faint and yet undiscovered because tidal stripping of a dominant GC population precedes significant stripping of the dark matter halos of these satellites. This scenario may alleviate some remaining tensions between CDM simulations and observations.

IMPACT OF H2-BASED STAR FORMATION MODEL ON THEz⩾ 6 LUMINOSITY FUNCTION AND THE IONIZING PHOTON BUDGET FOR REIONIZATION

We present the results of a numerical study examining the effect of H_2-based star formation (SF) model on the rest-frame UV luminosity function and star formation rate function (SFRF) of z>=6 galaxies, and the implications for reionization. Using cosmological hydrodynamical simulations outfitted with an H_2-SF model, we find good agreement with our previous results (non-H_2 SF model) and observations at Muv<=-18. However at Muv>-18, we find that the LF deviates from both our previous work and current observational extrapolations, producing significantly fewer low-luminosity galaxies and exhibiting additional turnover at the faint end. We constrain the redshift evolution of this turnover point using a modified Schechter function that includes additional terms to quantify the turnover magnitude (Muv^t) and subsequent slope (Beta). We find that Muv^t evolves from Muv^t=-17.33 (at z=8) to -15.38 (z=6), while Beta becomes shallower by \Delta Beta=0.22 during the same epoch. This occurs in an Muv range which will be observable by JWST. By integrating the SFRF, we determine that even though H_2-SF model significantly reduces the number density of low luminosity galaxies at Muv>-18, it does not suppress the total SFR density enough to affect the capability of SF to maintain reionization.

EVOLUTION OF THE QUASAR LUMINOSITY FUNCTION OVER 3 &lt;z&lt; 5 IN THE COSMOS SURVEY FIELD

We investigate the high-redshift quasar luminosity function (QLF) down to an apparent magnitude of I(AB) = 25 in the Cosmic Evolution Survey (COSMOS). Careful analysis of the extensive COSMOS photometry and imaging data allows us to identify and remove stellar and low-redshift contaminants, enabling a selection that is nearly complete for type-1 quasars at the redshifts of interest. We find 155 likely quasars at z > 3.1, 39 of which have prior spectroscopic confirmation. We present our sample in detail and use these confirmed and likely quasars to compute the rest-frame UV QLF in the redshift bins 3.1 < z < 3.5 and 3.5 < z < 5. The space density of faint quasars decreases by roughly a factor of four from z \sim 3.2 to z \sim 4, with faint-end slopes of {\beta} \sim -1.7 at both redshifts. The decline in space density of faint optical quasars at z > 3 is similar to what has been found for more luminous optical and X-ray quasars. We compare the rest-frame UV luminosity functions found here with the X-ray luminosity function at z > 3, and find that they evolve similarly between z \sim 3.2 and z \sim 4; however, the different normalizations imply that roughly 75% of X-ray bright active galactic nuclei (AGN) at z \sim 3 - 4 are optically obscured. This fraction is higher than found at lower redshift and may imply that the obscured, type-2 fraction continues to increase with redshift at least to z \sim 4. Finally, the implications of the results derived here for the contribution of quasars to cosmic reionization are discussed.

Lyman-α Emitters and Lyman-Break Galaxies at z = 3–6 in Cosmological SPH Simulations

Abstract We study the properties of Lyman-$\alpha $ emitters (LAEs) and Lyman-break galaxies (LBGs) at $z$$=$ 3–6 using cosmological SPH simulations. We investigate two simple scenarios for explaining the observed Ly$\alpha $ and rest-frame UV luminosity functions (LFs) of LAEs: (i) the “escape fraction” scenario, in which the effective escape fraction (including the IGM attenuation) of Ly$\alpha $ photons is $f_{{\rm Ly}\alpha}$$\approx$ 0.1 (0.15) at $z$$=$ 3 (6), and (ii) the “stochastic” scenario, in which the fraction of LAEs that are turned on at $z$$=$ 3 (6) is ${C_{\rm stoc}}$$\approx$ 0.07 (0.2) after correcting for the IGM attenuation. Our comparisons with a number of different observations suggest that the stochastic scenario is preferred over the escape fraction scenario. We find that the mean values of stellar mass, metallicity and black hole mass hosted by LAEs are all smaller in the stochastic scenario than in the escape fraction scenario. In our simulations, the galaxy stellar mass function evolves rapidly, as expected in hierarchical structure formation. However, its evolution is largely compensated by a beginning decline in the specific star formation rate, resulting in little evolution of the rest-frame UV LF from $z$$=$ 6 to 3. The rest-frame UV LF of both LAEs and LBGs at $z$$=$ 3 and 6 can be described well by the stochastic scenario provided the extinction is moderate, $E$($B$$-$$V$) $\approx$ 0.15, for both populations, although our simulation might be overpredicting the number of bright LBGs at $z$$=$ 6. We also discuss the correlation function and bias of LAEs. The Ly$\alpha $ LFs at $z$$=$ 6 in a field-of-view of 0.2 deg$^2$ show a significantly larger scatter owing to cosmic variance relative to that in a $1\ $deg$^2$ field, and the scatter seen in the current observational estimates of the Ly$\alpha $ LF can be accounted for by cosmic variance.

LYMAN BREAK GALAXIES ATz≈ 1.8-2.8:GALEX/NUV IMAGING OF THE SUBARU DEEP FIELD

Abridged: A photometric sample of ~7100 V<25.3 Lyman break galaxies (LBGs) has been selected by combining Subaru/Suprime-Cam BVRci'z' data with deep GALEX/NUV imaging of the Subaru Deep Field. Follow-up spectroscopy confirmed 24 LBGs at 1.5<z<2.7. Among the optical spectra, 12 have Ly-alpha emission with rest-frame equivalent widths of ~5-60AA. The success rate for identifying LBGs as NUV-dropouts at 1.5<z<2.7 is 86%. The rest-frame UV (1700AA) luminosity function (LF) is constructed from the photometric sample with corrections for stellar contamination and z<1.5 interlopers. The LF is 1.7+/-0.1 times higher than those of z~2 BXs and z~3 LBGs. Three explanations were considered, and it is argued that significantly underestimating low-z contamination or effective comoving volume is unlikely: the former would be inconsistent with the spectroscopic sample at 93% confidence, and the second explanation would not resolve the discrepancy. The third scenario is that different photometric selection of the samples yields non-identical galaxy populations, such that some BX galaxies are LBGs and vice versa. This argument is supported by a higher surface density of LBGs at all magnitudes while the redshift distribution of the two populations is nearly identical. This study, when combined with other star-formation rate (SFR) density UV measurements from LBG surveys, indicates that there is a rise in the SFR density: a factor of 3-6 (3-10) increase from z~5 (z~6) to z~2, followed by a decrease to z~0. This result, along with past sub-mm studies that find a peak at z~2 in their redshift distribution, suggest that z~2 is the epoch of peak star-formation. Additional spectroscopy is required to characterize the complete shape of the z~2 LBG UV LF via measurements of contamination and accurate distances.

Tracing the re-ionization-epoch intergalactic medium with metal absorption lines

IGM metal absorption lines observed in z>6 spectra offer the opportunity to probe early feedback processes, the nature of enriching sources, and the topology of reionization. We run high-resolution cosmological simulations including galactic outflows to study the observability and physical properties of 5 ions (C II, C IV, O I, Si II, Si IV) in absorption between z=8->5. We apply three cases for ionization conditions: Fully neutral, fully reionized, and a patchy model based on the flux from the nearest galaxy. We find that our simulations broadly fit available z~5-6 IGM metal-line data, although all observations cannot be accommodated with a single ionization condition. Variations in O I absorbers among sight lines seen by Becker et al. (2006) suggest significant neutral IGM patches down to z~6. Strong C IV absorbers at z~6 may be the result of ionization by their parent galaxy. Our outflows have typical speeds of ~200 km/s and mass loading factors of ~6. Such high mass loading is critical for enriching the IGM to the observed levels while curtailing star formation to match the observed z~6 rest-frame UV luminosity function. The volume filling factor of metals increases during this epoch, but only reaches ~1% for Z>10^(-3) Zsolar by z=5. C IV is an ideal tracer of IGM metals at z~5-6, with dropping global ionization fractions to either higher or lower redshifts. This results in a strongly increasing global Omega(C IV) from z=8->5, in contrast to its relative constancy from z=5->2. Our simulations do not support widespread early IGM enrichment from e.g. Pop III stars. High-z absorbers arise from metals on their first outward journey from galaxies, at distances less than 50 kpc. The galaxies responsible for early IGM enrichment have typical M*=10^(7.0-8.5) Msolar.

A Lyman Break Galaxy Candidate at z ~ 9

We report the discovery of a z ~ 9 Lyman break galaxy candidate, selected from the NICMOS Parallel Imaging Survey as a J-dropout with J110 − H160 = 1.7. Spitzer/IRAC photometry reveals that the galaxy has a blue H160 − 3.6 μm color and a spectral break between 3.6 and 4.5 μm. We interpret this break as the Balmer break and derive a best-fit photometric redshift of z ~ 9. We use Monte Carlo simulations to test the significance of this photometric redshift, and we show that there is a 96% probability of z ≥ 7. We estimate that the lower limit to the comoving number density of such galaxies at z ~ 9 is phi > 3.8 × 10^−6 Mpc^−3. If the high redshift of this galaxy is confirmed, this will indicate that the luminous end of the rest-frame UV luminosity function has not evolved substantially from z ~ 9 to z ~ 3. Still, some small degeneracy remains between this z ~ 9 model and models at z ~ 2–3; deep optical imaging (reaching IAB ~ 29) can rule out the lower z models.

Evolution of the rest-frame UV LF from z ~ 8 to z ~ 4

AbstractWe have assembled large samples of galaxies at redshift z ~ 4, 5 and 6 (totalling &gt;4300 objects, &gt;1000 objects, &gt;500 objects, respectively) from all the deep HST ACS and NICMOS data taken to date (over 2000 orbits of data). From these we have derived rest-frame UV luminosity functions, luminosity densities, and star formation rates in a very robust and consistent way to very faint luminosities (0.01L* to 0.04L*). The faint-end slopes α of these luminosity functions are remarkably uniform and steep (α ~ −1.7), indicating very little evolution from z ~ 6 to z ~ 4. The characteristic luminosity L* brightens considerably (by ~1 mag) over this period, but the overall change in the luminosity function is such as to lead to little change in the luminosity density and star formation rate over this time. We also have detected galaxies at z ~ 7 − 8 and set strong limits at z ~ 10 directly from deep HST NICMOS observations. Spitzer observations of these z ~ 7 galaxies have been used to estimate masses and ages, suggesting substantial formation at z ~ 10 or earlier. These results show that this hierachical build-up continues into the reionization epoch.

The Physical and Photometric Properties of High‐Redshift Galaxies in Cosmological Hydrodynamic Simulations

We study the physical and photometric properties of galaxies at z=4 in cosmological hydrodynamic simulations of a lambda-CDM universe. We focus on galaxies satisfying the GOODS B-dropout criteria. Our goals are: (1) to study the nature of high-redshift galaxies; (2) to test the simulations against published measurements of high-redshift galaxies; (3) to find relations between photometric measurements by HST/ACS (0.4 -- 1 micron) and Spitzer/IRAC (3.6 -- 8 micron) and the intrinsic physical properties of GOODS B-dropouts such as stellar mass, stellar age, dust reddening, and star-formation rate; and (4) to assess how representative the GOODS survey is at this epoch. Our simulations predict that high-redshift galaxies show strong correlations in star formation rate versus stellar mass, and weaker correlations versus environment and age, such that GOODS galaxies are predicted to be the most massive, most rapidly star-forming galaxies at that epoch, living preferentially in dense regions. The simulated rest-frame UV luminosity function (LF) and integrated luminosity density are in broad agreement with observations at z~4. The predicted rest-frame optical (observed 3.6 micron) LF is similar to the rest-frame UV LF, shifted roughly one magnitude brighter. We predict that GOODS detects less than 50% of the total stellar mass density formed in galaxies more massive than 10^8.7 M_sun by z=4, mainly because of brightness limits in the HST/ACS bands. The most rapidly star forming galaxies in our simulations have rates exceeding 1000 M_sun yr^-1, similar to observed sub-mm galaxies. The star formation rates of these galaxies show at most a mild excess (2--3x) over the rates that would be expected for their stellar mass. Whether these bright galaxies would be observable as LBGs depends on the uncertain effects of dust reddening.

Lyman Break Galaxies at z ∼ 5: Luminosity Function

Abstract We present the results of a search for Lyman break galaxies (LBGs) at $z \sim 5$ in a 618 square-arcmin field including the Hubble Deep Field-North (HDF-N) taken by the Subaru Prime Focus Camera. Utilizing the published redshift data of the HDF-N and its flanking fields, the color selection criteria were chosen so that LBGs could be picked out most efficiently and least contaminated by foreground objects. The numbers of detected LBG candidates were 96 in $23.0 \leq I_c \; (\mathrm{mag}) \leq 24.5$ and 310 in $23.0 \leq I_c \leq 25.5$. There is a hint of a deficiency of bright blue galaxies, although it is not as clear as has been suggested for LBGs at $z \sim 3$ to 4. With 305 LBG candidates in a 575 square-arcmin field, the rest-frame UV luminosity function of LBGs at $4.4 \lesssim z \lesssim 5.3$ was derived statistically by considering both the contamination by objects at the intermediate redshift and the incompleteness of the survey. The fraction of the contamination was estimated to be $\sim 50 \%$ in the faintest magnitude range. The completeness of the survey was $\sim 80\%$ at the bright part of the sample, and $\sim 20\%$ in the faintest magnitude range ($25.0 &amp;lt; I_c \leq 25.5$). The luminosity function of LBG candidates at $z \sim 5$ did not show a significant difference from those of LBGs at $z \sim 3$ and 4, though there might be a slight decrease in the fainter part. The UV luminosity density within the observational limit was 0.56–0.69 times smaller than that obtained for LBGs at $z \sim 3$, depending on the adopted cosmology and the integration range of the luminosity function. This decrease in the UV luminosity at $z \sim 5$ compared to that at $z \sim 3$ is due to the smaller number density of faint galaxies at $z \sim 5$. The similarity of the luminosity functions at redshifts 5 to 3 implies that most of the LBGs at $z \sim 5$ should have faded out at $z \sim 3$, and that the LBGs at $z \sim 5$ are different galaxies from those seen at $z \sim 3$, if we take the face values for the ages of the LBGs at $z \sim 3$ obtained by a SED fitting in which a continuous star formation in an individual galaxy was assumed. However, if the star formation in LBGs is sporadic, the similarity of the luminosity function at $z \sim 3$ and 5 would be explained. Such sporadic star formation has been suggested by hydrodynamical simulations and semi-analytic models with collisional starbursts, and the trend of the cosmic star formation history predicted by these studies resembles that estimated from an integration of the UV luminosity density within the observational limit.

Chemical abundances in a UV-selected sample of galaxies

We discuss the chemical properties of a sample of UV-selected intermediate-redshift (0≲z≲0.4) galaxies in the context of their physical nature and star-formation history. This work represents an extension of our previous studies of the rest-frame UV-luminosity function (Treyer et al.) and the star-formation properties of the same sample (Sullivan et al.). We revisit the optical spectra of these galaxies and perform further emission-line measurements restricting the analysis to those spectra with the full set of emission lines required to derive chemical abundances. Our final sample consists of 68 galaxies with heavy-element abundance ratios and both UV and CCD B-band photometry. Diagnostics based on emission-line ratios show that all but one of the galaxies in our sample are powered by hot, young stars rather than by an AGN. Oxygen-to-hydrogen (O/H) and nitrogen-to-oxygen (N/O) abundance ratios are compared with those of various local and intermediate-redshift samples. Our UV-selected galaxies span a wide range of oxygen abundances, from ∼0.1 to 1 Z⊙, intermediate between low-mass H II galaxies and massive starburst nuclei. For a given oxygen abundance, most have strikingly low N/O values. Moreover, UV-selected and H II galaxies systematically deviate from the usual metallicity–luminosity relation in the sense of being more luminous by 2–3 mag. Adopting the ‘delayed-release’ chemical evolution model, we propose our UV-selected sources are observed at a special stage in their evolution, following a powerful starburst that enriched their ISM in oxygen and temporarily lowered their mass-to-light ratios. We discuss briefly the implications of our conclusions on the nature of similarly selected high-redshift galaxies.