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تسجيل مستخدم جديدLyman Break Galaxies at z~5: Rest-frame UV Spectra II
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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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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 objec
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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. E
ight 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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lor 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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