We present spectroscopy of 15 star-forming BzK galaxies (sBzKs) with K(AB)<23 in the Subaru Deep Field, for which Halpha and some other emission lines are detected in 0.9 to 2.3 micron spectra with a resolution of R=500. Using Halpha luminosities, we obtain star formation rates (SFRs), and then specific SFRs (SSFRs) dividing SFRs by stellar masses, which are derived from SED fitting to BVRi'z'K photometry. It is found that sBzKs with higher stellar masses have larger SFRs. A negative correlation is seen between stellar mass and SSFR, which is consistent with the previous results for z~2 galaxies. This implies that a larger growth of stellar mass occurs in less massive galaxies. In addition, gas-phase oxygen abundances, 12+log(O/H), are derived from the ratio of NII(lambda 6584) to Halpha using the N2 index method. We have found a correlation between stellar mass and oxygen abundance in the sense that more massive sBzKs tend to be more metal rich, which is qualitatively consistent with the relation for UV-selected z~2 galaxies. However, the metallicity of the sBzKs is ~0.2 dex higher than that of UV-selected galaxies with similar stellar masses, which is significant considering the small uncertainties. The sBzKs in our sample have redder R-K colors than the UV-selected galaxies. This galaxy color-dependence in the oxygen abundance may be caused by older or dustier galaxies having higher metallicities at z~2.

We carried out extended spectroscopic confirmations of Lyα emitters (LAEs) at z = 6.5 and 5.7 in the Subaru Deep Field. Now, the total number of spectroscopically confirmed LAEs is 45 and 54 at z = 6.5 and 5.7, respectively, and at least 81% (70%) of our photometric candidates at z = 6.5 (5.7) have been spectroscopically identified as real LAEs. We made careful measurements of the Lyα luminosity, both photometrically and spectroscopically, to accurately determine the Lyα and rest-UV luminosity functions (LFs). The substantially improved evaluation of the Lyα LF at z = 6.5 shows an apparent deficit from z = 5.7 at least at the bright end, and a possible decline even at the faint end, though small uncertainties remain. The rest-UV LFs at z = 6.5 and 5.7 are in good agreement, at least at the bright end, in clear contrast to the differences seen in the Lyα LF. These results imply an increase in the neutral fraction of the intergalactic medium from z = 5.7 to 6.5. The rest-frame equivalent width (EW0) distribution at z = 6.5 seems to be systematically smaller than z = 5.7, and it shows an extended tail toward larger EW0. The bright end of the rest-UV LF can be reproduced from the observed Lyα LF and a reasonable EW0-UV luminosity relation. Integrating this rest-UV LF provides the first measurement of the contribution of LAEs to the photon budget required for reionization. The derived UV LF suggests that the fractional contribution of LAEs to the photon budget among Lyman break galaxies significantly increases toward faint magnitudes. Low-luminosity LAEs could dominate the ionizing photon budget, though this inference depends strongly on the uncertain faint-end slope of the Lyα LF. © 2011. The American Astronomical Society. All rights reserved.

We present the properties of Ly Alpha emitters (LAEs) at z = 5.7 in the Subaru Deep Field. A photometric sample of 89 LAE candidates is constructed from narrow-band (NB816) data down to NB816 = 26.0 (AB) in a continuous 725 arcmin^2 area. Spectra of 39 objects satisfying the photometric selection criteria for LAEs were obtained with Subaru and Keck II Telescopes, among which 28 were confirmed LAEs, one was a nearby galaxy, and eight were unclassified. We also obtained spectra of another 24 NB816-excess objects in the field, identifying six additional LAEs. We find that the Ly Alpha luminosity function derived from the photometric sample is reproduced well by a Schechter function with L* = (7.9+3.0-2.2) x 10^42 erg/s and phi* = (6.3+3.0-2.0) x 10^-4 Mpc^-3 for alpha = -1.5 (fixed) over the whole luminosity range of L ~= 3x10^42 - 3x10^43 erg/s. We then measure rest-frame Ly Alpha equivalent widths (EWs) for the confirmed LAEs, to find that the median among the 28 objects satisfying the photometric selection criteria is W_0^i = 233 A. We infer that 30% - 40% of LAEs at z=5.7 exceed W_0^i = 240 A. These large-EW objects probably cannot be accounted for by ordinary star-forming populations with a Salpeter IMF. We also find that LAEs with fainter far-UV luminosities have larger EWs. Finally, we derive the far-UV luminosity function of LAEs down to M_UV ~= -19.6 using the photometric sample, and compare it with that of Lyman-break galaxies (LBGs). We find that as high as about 80% of LBGs at z ~ 6 have W_0^i >= 100 A, in sharp contrast to lower-z counterparts.

We explored the clustering properties of Lyman break galaxies at z = 4 and 5 with an angular two-point correlation function on the basis of the very deep and wide Subaru Deep Field data. We confirmed the previous result that the clustering strength of LBGs depends on the UV luminosity in the sense that brighter LBGs are more strongly clustered. In addition, we found an apparent dependence of the correlation function slope on UV luminosity for LBGs at both z = 4 and 5. More luminous LBGs have a steeper correlation function. The bias parameter was found to be a scale-dependent function for bright LBGs, whereas it appears to be almost scale-independent for faint LBGs. Luminous LBGs have a higher bias at smaller angular scales, which decreases as the scale increases. To compare these observational results, we constructed numerical mock LBG catalogs based on a semianalytic model of hierarchical clustering combined with high-resolution N-body simulation, carefully mimicking the observational selection effects. The luminosity functions and the overall correlation functions for LBGs at z = 4 and 5 predicted by this mock catalog were found to be almost consistent with the observation. The observed dependence of the clustering on UV luminosity was not reproduced by the model, unless subsamples of distinct halo mass were considered. That is, LBGs belonging to more massive dark halos had steeper and larger amplitude correlation functions. With this model, we found that LBG multiplicity in massive dark halos amplifies the clustering strength at small scales, which steepens the correlation function. The hierarchical clustering model could therefore be reconciled with the observed luminosity dependence of the correlation function if there is a tight correlation between UV luminosity and halo mass. Our finding that the slope of the correlation function depends on luminosity could be an indication that massive dark halos hosted multiple bright LBGs. © 2006. The American Astronomical Society. All rights reserved.