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Quasars (QSOs) hosting supermassive black holes are believed to reside in massive halos harboring galaxy overdensities. However, many observations revealed average or low galaxy densities around $z\gtrsim6$ QSOs. This could be partly because they measured galaxy densities in only tens of arcmin$^2$ around QSOs and might have overlooked potential larger scale galaxy overdensities. Some previous studies also observed only Lyman break galaxies (LBGs, massive older galaxies) and missed low mass young galaxies like Ly$��$ emitters (LAEs) around QSOs. Here we present observations of LAE and LBG candidates in $\sim700$ arcmin$^2$ around a $z=6.61$ luminous QSO using Subaru Telescope Suprime-Cam with narrow/broadbands. We compare their sky distributions, number densities and angular correlation functions with those of LAEs/LBGs detected in the same manner and comparable data quality in our control blank field. In the QSO field, LAEs and LBGs are clustering in 4-20 comoving Mpc angular scales, but LAEs show mostly underdensity over the field while LBGs are forming $30\times60$ comoving Mpc$^2$ large scale structure containing 3-$7��$ high density clumps. The highest density clump includes a bright (23.78 mag in the narrowband) extended ($\gtrsim 16$ kpc) Ly$��$ blob candidate, indicative of a dense environment. The QSO could be part of the structure but is not located exactly at any of the high density peaks. Near the QSO, LAEs show underdensity while LBGs average to $4��$ excess densities compared to the control field. If these environments reflect halo mass, the QSO may not be in the most massive halo, but still in a moderately massive one., 35 pages, 15 figures, 2 tables, accepted for publication in The Astrophysical Journal

We detect 20 $z=7.0$ Ly$��$ emitter (LAE) candidates to $L({\rm Ly}��) \geq 2 \times 10^{42}$ erg s$^{-1}$ or $0.3$ $L^*_{z=7}$ and in $6.1\times 10^5$ Mpc$^3$ volume in the Subaru Deep Field and the Subaru/XMM-Newton Deep Survey field by 82 and 37 hours of Subaru Suprime-Cam narrowband NB973 and reddest optical $y$-band imaging. We compare their Ly$��$ and UV luminosity functions (LFs) and densities and Ly$��$ equivalent widths (EWs) to those of $z=5.7$, 6.6 and 7.3 LAEs from previous Suprime-Cam surveys. The Ly$��$ LF (density) rapidly declines by a factor of $\times$1.5 (1.9) in $L({\rm Ly}��)$ at $z=5.7-6.6$ (160 Myr), $\times$1.5 (1.6) at $z=6.6-7.0$ (60 Myr) at the faint end and $\times$2.0 (3.8) at $z=7.0-7.3$ (40 Myr). Also, in addition to the systematic decrease in EW at $z=5.7-6.6$ previously found, 2/3 of the $z=7.0$ LAEs detected in the UV continuum exhibit lower EWs than the $z=6.6$ ones. Moreover, while the UV LF and density do not evolve at $z=5.7-6.6$, they modestly decline at $z=6.6-7.0$, implying galaxy evolution contributing to the decline of the Ly$��$ LF. Comparison of the $z=7.0$ Ly$��$ LF to the one predicted by an LAE evolution model further reveals that galaxy evolution alone cannot explain all the decline of Ly$��$ LF. If we attribute the discrepancy to Ly$��$ attenuation by neutral hydrogen, the intergalactic medium transmission of Ly$��$ photons at $z=7.0$ would be $T_{{\rm Ly}��}^{\rm IGM} \leq 0.6-0.7$. It is lower (higher) than $T_{{\rm Ly}��}^{\rm IGM}$ at $z=6.6$ (7.3) derived by previous studies, suggesting rapid increase in neutral fraction at $z > 6$., 37 Pages, 22 Figures, 10 Tables, Accepted for publication in ApJ

We study the extent to which very bright (-23.0 < MUV < -21.75) Lyman-break selected galaxies at redshifts z~7 display detectable Lya emission. To explore this issue, we have obtained follow-up optical spectroscopy of 9 z~7 galaxies from a parent sample of 24 z~7 galaxy candidates selected from the 1.65 sq.deg COSMOS-UltraVISTA and SXDS-UDS survey fields using the latest near-infrared public survey data, and new ultra-deep Subaru z'-band imaging (which we also present and describe in this paper). Our spectroscopy has yielded only one possible detection of Lya at z=7.168 with a rest-frame equivalent width EW_0 = 3.7 (+1.7/-1.1) Angstrom. The relative weakness of this line, combined with our failure to detect Lya emission from the other spectroscopic targets allows us to place a new upper limit on the prevalence of strong Lya emission at these redshifts. For conservative calculation and to facilitate comparison with previous studies at lower redshifts, we derive a 1-sigma upper limit on the fraction of UV bright galaxies at z~7 that display EW_0 > 50 Angstrom, which we estimate to be < 0.23. This result may indicate a weak trend where the fraction of strong Lya emitters ceases to rise, and possibly falls between z~6 and z~7. Our results also leave open the possibility that strong Lya may still be more prevalent in the brightest galaxies in the reionization era than their fainter counterparts. A larger spectroscopic sample of galaxies is required to derive a more reliable constraint on the neutral hydrogen fraction at z~7 based on the Lya fraction in the bright galaxies., 20 pages, 7 figures, accepted for publication in ApJ

Accepted: 2014-08-20, 資料番号: SA1004964000