Search

We present the cross-correlation between 151 luminous quasars (MUV < -26) and 179 protocluster candidates at z ~ 3.8, extracted from the Wide imaging survey (~121 deg2) performed as part of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). We find that only two out of 151 quasars reside in regions that are more overdense compared to the average field at >4 σ. The distributions of the distances between quasars and the nearest protoclusters and the significance of the overdensity at the positions of quasars are statistically identical to those found for g-dropout galaxies, suggesting that quasars tend to reside in almost the same environment as star-forming galaxies at this redshift. Using stacking analysis, we find that the average density of g-dropout galaxies around quasars is slightly higher than that around g-dropout galaxies on 1.0-2.5 pMpc scales, while at <0.5 pMpc that around quasars tends to be lower. We also find that quasars with higher UV luminosity or with more massive black holes tend to avoid the most overdense regions, and that the quasar near-zone sizes are anti-correlated with overdensity. These findings are consistent with a scenario in which luminous quasars at z ~ 4 reside in structures that are less massive than those expected for the progenitors of today's rich clusters of galaxies, and possibly that luminous quasarsmay be suppressing star formation in their close vicinity. [ABSTRACT FROM AUTHOR]

We conduct a systematic search for galaxy protoclusters at z ~ 3.8 based on the latest internal data release (S16A) of the Hyper Suprime-Cam Subaru strategic program (HSC-SSP). In the Wide layer of the HSC-SSP, we investigate the large-scale projected sky distribution of g-dropout galaxies over an area of 121 deg2, and identify 216 large-scale overdense regions (>4 σ overdensity significance) that are likely protocluster candidates. Of these, 37 are located within 8΄ (3.4 physical Mpc) of other protocluster candidates of higher overdensity, and are expected to merge into a single massive structure by z = 0. Therefore, we find 179 unique protocluster candidates in our survey. A cosmological simulation that includes projection effects predicts that more than 76% of these candidates will evolve into galaxy clusters with halo masses of at least 1014 M⊙ by z = 0. The unprecedented size of our protocluster candidate catalog allows us to perform, for the first time, an angular clustering analysis of the systematic sample of protocluster candidates. We find a correlation length of 35.0 h-1 Mpc. The relation between correlation length and number density of z ~ 3.8 protocluster candidates is consistent with the prediction of the ΛCDM model, and the correlation length is similar to that of rich clusters in the local universe. This result suggests that our protocluster candidates are tracing similar spatial structures to those expected from the progenitors of rich clusters, and enhances the confidence that our method for identifying protoclusters at high redshifts is robust. In years to come, our protocluster search will be extended to the entire HSC-SSP Wide sky coverage of ~ 1400 deg2 to probe cluster formation over a wide redshift range of z ~ 2-6. [ABSTRACT FROM AUTHOR]

We discuss the host galaxy metallicity distribution of all long gamma-ray bursts (GRBs) whose redshifts are known to be <0.4, including newly obtained spectroscopic datasets of the host galaxies of GRB060614, 090417B, and 130427A. We compare the metallicity distribution of the low-redshift sample to the model predictions, and constrain the relation between metallicity and GRB occurrence. We take account of spatial variation of metallicities among star-forming regions within a galaxy. We found that the models in which only low-metallicity stars produce GRBs with a sharp cutoff of GRB production efficiency around 12+log(O/H) ∼ 8.3 can reproduce the observed distribution well, while the models with no metallicity dependence are not consistent with the observations.We also discuss possible sampling biases we may suffer by collecting long GRBs whose redshifts are known, presenting the photometric observations of the host galaxy of GRB111225A at z = 0.297 whose redshift has been undetermined until ∼2.3 yr after the burst. [ABSTRACT FROM AUTHOR]

We present the results of an halo occupation distribution (HOD) analysis of star-forming galaxies at z ~ 2. We obtained high-quality angular correlation functions based on a large sgzK sample, which enabled us to carry out the HOD analysis. The mean halo mass and the HODmass parameters are found to increase monotonically with increasing K-band magnitude, suggesting that more luminous galaxies reside in more massive dark haloes. The luminosity dependence of the HOD mass parameters was found to be the same as in the local Universe; however, the masses were larger than in the local Universe over all ranges of magnitude. This implies that galaxies at z ~ 2 tend to form in more massive dark haloes than in the local Universe, a process known as downsizing. By analysing the dark halo mass evolution using the extended Press-Schechter formalism and the number evolution of satellite galaxies in a dark halo, we find that faint Lyman break galaxies at z ~ 4 could evolve into the faintest sgzKs (22.0 < K ≤ 23.0) at z ~ 2 and into the Milky-Way-like galaxies or elliptical galaxies in the local Universe, whereas the most luminous sgzKs (18.0 ≤ K ≤ 21.0) could evolve into the most massive systems in the local Universe. The stellar-to-halo mass ratio (SHMR) of the sgzKs was found to be consistent with the prediction of the model, except that the SHMR of the faintest sgzKs was smaller than the prediction at z ~ 2. This discrepancy may be explained by the confinement of our samples to star-forming galaxies. [ABSTRACT FROM AUTHOR]

We present the results of clustering analysis on z ~ 2 star-forming galaxies. By combining our data with data from publicly available archives, we collect g-, zB/z- and K-band imaging data over 5.2 deg2, which represents the largest area BzK/gzK survey. We apply colour corrections to translate our filter set to those used in the original BzK selection for the gzK selection. Because of the wide survey area, we obtain a sample of 41 112 star-forming gzK galaxies at z ~ 2 (sgzK galaxies) down to KAB < 23.0, and we determine high-quality two-point angular correlation functions (ACFs). Our ACFs show an apparent excess from power-law behaviour at small angular scale (≲ 0°.01), which corresponds to the virial radius of a dark halo at z ~ 2 with a mass of ~1013 MΘ. We find that the correlation lengths are consistent with the previous estimates over the whole magnitude range; however, our results are evaluated with a smaller margin of error than that in previous studies. The large amount of data enables us to determine ACFs differentially depending on the luminosity of the subset of the data. The mean halo mass of faint sgzK galaxies (22.0 < K ≤ 23.0) was found to be 〈Mh〉=(1.32-0.12+0.09)×1012h-1 MΘ, whereas bright sgzK galaxies (18.0 ≤ K ≤ 21.0) were found to reside in dark haloes with a mass of 〈Mh〉=(3.26-1.02+1.23)×1013h-1 MΘ. [ABSTRACT FROM AUTHOR]