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Register a new userLyman Break Galaxies at $zsim5$: Rest-Frame UV Spectra
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Masataka Ando
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We report initial results for spectroscopic observations of candidates of Lyman Break Galaxies (LBGs) at $zsim5$ in a region centered on the Hubble Deep Field-North by using the Faint Object Camera and Spectrograph attached to the Subaru Telescope. Eight objects with $I_Cleq25.0$ mag, including one AGN, are confirmed to be at $4.5<z<5.2$. The rest-frame UV spectra of seven LBGs commonly show no or weak Lyalpha emission line (rest-frame equivalent width of 0-10AA) and relatively strong low-ionization interstellar metal absorption lines of SiII $lambda$1260, OI+SiII $lambda$1303, and CII $lambda$1334 (mean rest-frame equivalent widths of them are $-1.2 sim -5.1 $AA). These properties are significantly different from those of the mean rest-frame UV spectrum of LBGs at $zsim3$, but are quite similar to those of subgroups of LBGs at $zsim3$ with no or weak Lyalpha emission. The weakness of Lyalpha emission and strong low-ionization interstellar metal absorption lines may indicate that these LBGs at $zsim5$ are chemically evolved to some degree and have a dusty environment. Since the fraction of such LBGs at $zsim5$ in our sample is larger than that at $zsim3$, we may witness some sign of evolution of LBGs from $zsim5$ to $zsim3$, though the present sample size is very small. It is also possible, however, that the brighter LBGs tend to show no or weak Lyalpha emission, because our spectroscopic sample is bright (brighter than $L^{ast}$) among LBGs at $zsim5$. More observations are required to establish spectroscopic nature of LBGs at $zsim5$.
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We present results of optical spectroscopic observations of candidates of Lyman Break Galaxies (LBGs) at $z sim 5$ in the region including the GOODS-N and the J0053+1234 region by using GMOS-N and GMOS-S, respectively. Among 25 candidates, five objects are identified to be at $z sim 5$ (two of them were already identified by an earlier study) and one object very close to the color-selection window turned out to be a foreground galaxy. With this spectroscopically identified sample and those from previous studies, we derived the lower limits on the number density of bright ($M_{UV}<-22.0$ mag) LBGs at $z sim 5$. These lower limits are comparable to or slightly smaller than the number densities of UV luminosity functions (UVLFs) that show the smaller number density among $z sim 5$ UVLFs in literature. However, by considering that there remain many LBG candidates without spectroscopic observations, the number density of bright LBGs is expected to increase by a factor of two or more. The evidence for the deficiency of UV luminous LBGs with large Ly$alpha$ equivalent widths was reinforced. We discuss possible causes for the deficiency and prefer the interpretation of dust absorption.
We present the results of spectroscopy of Lyman Break Galaxies (LBGs) at z~5 in the J0053+1234 field with the Faint Object Camera and Spectrograph on the Subaru telescope. Among 5 bright candidates with z < 25.0 mag, 2 objects are confirmed to be at z~5 from their Ly alpha emission and the continuum depression shortward of Ly alpha. The EWs of Ly alpha emission of the 2 LBGs are not so strong to be detected as Ly alpha emitters, and one of them shows strong low-ionized interstellar (LIS) metal absorption lines. Two faint objects with z geq 25.0 mag are also confirmed to be at z~5, and their spectra show strong Ly alpha emission in contrast to the bright ones. These results suggest a deficiency of strong Ly alpha emission in bright LBGs at z~5, which has been discussed in our previous paper. Combined with our previous spectra of LBGs at z~5 obtained around the Hubble Deep Field-North (HDF-N), we made a composite spectrum of UV luminous (M_1400 leq -21.5 mag) LBGs at z~5. The resultant spectrum shows a weak Ly alpha emission and strong LIS absorptions which suggests that the bright LBGs at z~5 have chemically evolved at least to ~0.1 solar metallicity. For a part of our sample in the HDF-N region, we obtained near-to-mid infrared data, which constraint stellar masses of these objects. With the stellar mass and the metallicity estimated from LIS absorptions, the metallicities of the LBGs at z~5 tend to be lower than those of the galaxies with the same stellar mass at z lesssim 2, although the uncertainty is very large.
We present the results of Spectral Energy Distribution (SED) fitting analysis for Lyman Break Galaxies (LBGs) at $zsim5$ in the GOODS-N and its flanking fields. From the SED fitting for $sim100$ objects, we found that the stellar masses range from $10^{8}$ to $10^{11}M_{odot}$ with a median value of $4times10^{9}M_{odot}$. By using the large sample of galaxies at $zsim5$, we construct the stellar mass function (SMF) with incompleteness corrections. By integrating down to $10^{8}M_{odot}$, the cosmic stellar mass density at $zsim5$ is calculated to be $7times10^{6}M_{odot}textrm{Mpc}^{-3}$.
This work explores from a statistical point of view the rest-frame Far-ultraviolet (FUV) to Far-infrared (FIR) emission of a population of Lyman break galaxies (LBGs) at $zsim3$ that cannot be individually detected from current FIR observations. We perform a stacking analysis over a sample of $sim$17000 LBGs at redshift $2.5<z<3.5$ in the COSMOS field. The sample is binned as a function of UV luminosity ($L_{mathrm{FUV}}$), UV continuum slope ($beta_{mathrm{UV}}$), and stellar mass (M$_{*}$), and then, stacked at optical ($BVriz$ bands), near-infrared ($YJHKs$ bands), IRAC (3.6, 4.5, 5.6 and 8.0 $mu$m), MIPS (24$mu$m), PACS (100 and 160~$mu$m), SPIRE (250, 350, and 500~$mu$m), and AzTEC (1.1mm) observations. We obtain thirty rest-frame FUV-to-FIR spectral energy distribution (SEDs) of LBGs at $zsim3$, and analyse them with CIGALE SED-fitting analysis code. We are able to derive fully consistent physical parameters (M$_{*}$, $beta_{mathrm{UV}}$, $L_{mathrm{FUV}}$, $L_{mathrm{IR}}$, A$_{FUV}$, SFR, and slope of the dust attenuation law), and build a semi-empirical library of thirty rest-frame FUV-to-FIR stacked LBG SEDs as a function of $L_{mathrm{FUV}}$, $beta_{mathrm{UV}}$, and M$_{*}$. We used the so-called IR-excess ($IRX equiv L_{mathrm{IR}} / L_{mathrm{FUV}}$) to investigate the dust attenuation as a function of $beta_{mathrm{UV}}$ and M$_{*}$. Additionally, the SED-fitting analysis results provide a diversity of dust attenuation curve along the LBG sample, and their slope are well correlated with M$_{*}$. Stepper dust attenuations curves than Calzettis are favoured in low stellar mass LBGs ($log(M_{*} [M_{odot}]) < 10.25$), while grayer ones are favoured in high stellar mass LBGs ($log(M_{*} [M_{odot}]) > 10.25$).
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 $zsim3$ 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.
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