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Register a new userLyman Break Galaxies at z~5: Luminosity Function
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(abridged) We present results of a search for Lyman break galaxies (LBGs) at z ~ 5 in a 618 square-arcmin field including the HDF-N taken by Subaru Prime Focus Camera. Utilizing the published redshift data of the HDF-N and its flanking fields, the color selection criteria are chosen so that LBGs are picked out most efficiently and least contaminated by foreground objects. The numbers of LBG candidates detected are 310 in 23.0 < I_c < 25.5. The rest-frame UV luminosity function(LF) of LBGs at z ~ 5 is derived statistically. The fraction of contamination is estimated to be ~50% in the faintest magnitude range. The completeness of the survey is ~80% at the bright part of the sample, and ~20% in the faintest magnitude range (25.0 < I_c <= 25.5). The LF of LBG candidates at z ~ 5 does not show a significant difference from those at z ~ 3 and 4, though there might be a slight decrease in the fainter part. The UV luminosity density within the observational limit is 0.56 - 0.69 times smaller than that obtained for LBGs at z ~ 3, depending on the adopted cosmology and the integration range of the LF. The similarity of the LFs at redshifts 5 to 3 implies that most of LBGs at z ~ 5 should have faded out at z ~ 3 and LBGs at z ~ 5 are different galaxies from those seen at z ~ 3, if we take face values for ages of the LBGs at z ~ 3 obtained by the SED fitting in which a continuous star formation in an individual galaxy is assumed. However, if the star formation in LBGs is sporadic, the similarity of the LF at z ~ 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 to that estimated from the UV luminosity density within the observational limit.
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We present the results of a study of a large sample of luminous (z{AB}<26) Lyman break galaxies (LBGs) in the redshift interval 4.7<z<6.3, selected from a contiguous 0.63 square degree area covered by the UKIDSS Ultra Deep Survey (UDS) and the Subaru XMM-Newton Survey (SXDS). Utilising the large area coverage and the excellent available optical+nearIR data, we use a photometric redshift analysis to derive a new, robust, measurement of the bright end (L>L*) of the UV-selected luminosity function at high redshift. When combined with literature studies of the fainter LBG population, our new sample provides improved constraints on the luminosity function of redshift 5<z<6 LBGs over the luminosity range 0.1L*<L<10L*. A maximum likelihood analysis returns best-fitting Schechter function parameters of M*_1500=-20.73, phi*=0.0009 Mpc^-3 and alpha=-1.66 for the luminosity function at z=5, and M*_1500 = -20.04, phi*=0.0018 Mpc^-3 and alpha=-1.71 at z=6. In addition, an analysis of the angular clustering properties of our LBG sample demonstrates that luminous 5<z<6 LBGs are strongly clustered (r_0 = 8.1 Mpc), and are consistent with the occupation of dark matter halos with masses of ~10^{11.5-12.0} Msun. Moreover, by stacking the available multi-wavelength imaging data for the high-redshift LBGs it is possible to place useful constraints on their typical stellar mass. The results of this analysis suggest that luminous LBGs at 5<z<6 have an average stellar mass of ~10^10 Msun, consistent with the results of the clustering analysis assuming plausible values for the ratio of stellar to dark matter. Finally, by combining our luminosity function results with those of the stacking analysis we derive estimates of ~1x10^7 Msun Mpc^-3 and 4x10^6 Msun Mpc^-3 for the stellar mass density at z~5 and z~6 respectively.
(abridged) We report the UV luminosity function (LF) of Lyman break galaxies at z~5 derived from a deep and wide survey using the Subaru/Suprime-Cam. Target fields consist of two blank regions of the sky (the HDF-N and J0053+1234), and the total effective surveyed area is 1290 sqarcmin. Applications of carefully determined colour selection criteria in V-I and I-z yield a detection of 853 candidates with zAB<26.5 mag. The derived UVLF at z~5 shows no significant change in the number density of bright (L>=L*_z=3) LBGs from that at z~3, while there is a significant decline in the LFs faint end with increasing lookback time. This result means that the evolution of the number densities is differential with UV luminosity: the number density of UV luminous objects remains almost constant from z~5 to 3 while the number density of fainter objects gradually increases with cosmic time. This trend becomes apparent thanks to the small uncertainties in number densities both in the bright and faint parts of LFs at different epochs that are made possible by the deep and wide surveys. We discuss the origins of this differential evolution and suggest that our observational findings are consistent with the biased galaxy evolution scenario: a galaxy population hosted by massive dark haloes starts active star formation preferentially at early cosmic time, while less massive galaxies increase their number density later. We also calculated the UV luminosity density by integrating the UVLF and at z~5 found it to be 38.8% of that at z~3 for the luminosity range L>0.1 L^*_z=3. By combining our results with those from the literature, we find that the cosmic UV luminosity density marks its peak at z=2-3 and then slowly declines toward higher redshift.
We present the results of Spectral Energy Distribution(SED) fitting analysis for Lyman Break Galaxies(LBGs) at z~5 in the GOODS-N and its flanking fields (the GOODS-FF). With the publicly available IRAC images in the GOODS-N and IRAC data in the GOODS-FF, we constructed the rest-frame UV to optical SEDs for a large sample (~100) of UV-selected galaxies at z~5. Comparing the observed SEDs with model SEDs generated with a population synthesis code, we derived a best-fit set of parameters (stellar mass, age, color excess, and star formation rate) for each of sample LBGs. The derived stellar masses range from 10^8 to 10^11M_sun with a median value of 4.1x10^9M_sun. The comparison with z=2-3 LBGs shows that the stellar masses of z~5 LBGs are systematically smaller by a factor of 3-4 than those of z=2-3 LBGs in a similar rest-frame UV luminosity range. The star formation ages are relatively younger than those of the z=2-3 LBGs. We also compared the results for our sample with other studies for the z=5-6 galaxies. Although there seem to be similarities and differences in the properties, we could not conclude its significance. We also derived a stellar mass function of our sample by correcting for incompletenesses. Although the number densities in the massive end are comparable to the theoretical predictions from semi-analytic models, the number densities in the low-mass part are smaller than the model predictions. By integrating the stellar mass function down to 10^8 M_sun, the stellar mass density at z~5 is calculated to be (0.7-2.4)x10^7M_sun Mpc^-3. The stellar mass density at z~5 is dominated by massive part of the stellar mass function. Compared with other observational studies and the model predictions, the mass density of our sample is consistent with general trend of the increase of the stellar mass density with time.
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.
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