Abstract
We present, for the first time, dark matter halo (DMH) mass measurement of quasars at
z
∼ 6 based on a clustering analysis of 107 quasars. Spectroscopically identified quasars are ...homogeneously extracted from the Hyper Suprime-Cam Strategic Survey Program wide layer over 891 deg
2
. We evaluate the clustering strength by three different autocorrelation functions: projected correlation function, angular correlation function, and redshift–space correlation function. The DMH mass of quasars at
z
∼ 6 is evaluated as
5.0
−
4.0
+
7.4
×
10
12
h
−
1
M
⊙
with the bias parameter
b
= 20.8 ± 8.7 by the projected correlation function. The other two estimators agree with these values; though, each uncertainty is large. The DMH mass of quasars is found to be nearly constant ∼10
12.5
h
−1
M
⊙
throughout cosmic time, suggesting that there is a characteristic DMH mass where quasars are always activated. As a result, quasars appear in the most massive halos at
z
∼ 6, but in less extreme halos thereafter. The DMH mass does not appear to exceed the upper limit of 10
13
h
−1
M
⊙
, which suggests that most quasars reside in DMHs with
M
halo
<
10
13
h
-
1
M
⊙
across most of the cosmic time. Our results supporting a significant increasing bias with redshift are consistent with the bias evolution model with inefficient active galactic nucleus feedback at
z
∼ 6. The duty cycle (
f
duty
) is estimated as 0.019 ± 0.008 by assuming that DMHs in some mass interval can host a quasar. The average stellar mass is evaluated from stellar-to-halo mass ratio as
M
*
=
6.5
−
5.2
+
9.6
×
10
10
h
−
1
M
⊙
, which is found to be consistent with C
ii
observational results.
Abstract In this paper, we present a Ly α halo (LAH) identified by stacking ∼3300 Ly α emitters (LAEs) at z = 2.2–2.3. We carry out imaging observations and data reduction with Subaru/Hyper ...Suprime-Cam. Our total survey area is ∼12 deg 2 and the imaging depths are 25.5–27.0 mag. Using the imaging data, we select 1240 and 2101 LAE candidates at z = 2.2 and 2.3, respectively. We carry out spectroscopic observations of our LAE candidates and data reduction with Magellan/IMACS to estimate the contamination rate of our LAE candidates. We find that the contamination rate of our sample is low (8%). We stack our LAE candidates with a median stacking method to identify the LAH at z = 2. We show that our LAH is detected until ∼100 kpc at the 2 σ significance level and likely extended to ∼200 kpc at a surface brightness level of ∼10 −20 erg s −1 cm −2 arcsec −2 . Compared to those of previous studies, our LAH is brighter at radii of ∼25–100 kpc, which is not likely caused by the contamination in our sample but by the different redshifts, fields, and selection methods instead. To investigate how central galaxies affect surrounding LAHs, we divide our LAEs into subsamples based on the Ly α luminosity ( L Ly α ), rest-frame Ly α equivalent width (EW 0 ), and UV magnitude ( M uv ). We stack the subsamples and find that higher L Ly α , smaller EW 0 , and brighter M uv cause more extended halos. Our results suggest that more massive LAEs generally have more extended LAHs.
We report the rest-frame ultraviolet luminosity function of g-dropout galaxies in 177 protocluster candidates (PC UVLF) at z ∼ 4 selected in the Hyper Suprime-Cam Subaru Strategic Program. Comparing ...it with the UVLF of field galaxies at the same redshift, we find that the PC UVLF shows a significant excess toward the bright end. This excess cannot be explained by the contribution of only active galactic nuclei, and we also find that this excess is more significant in higher density regions. Assuming that all protocluster members are located on the star formation main sequence, the PC UVLF can be converted into a stellar mass function. Consequently, our protocluster members are inferred to have a 2.8 times more massive characteristic stellar mass than that of the field Lyman break galaxies at the same redshift. This study, for the first time, clearly shows that the enhancement in star formation or stellar mass in overdense regions can generally be seen as early as at z ∼ 4. We also estimate the star formation rate density (SFRD) in protocluster regions as 6%-20% of the cosmic SFRD, based on the measured PC UVLF after correction for the selection incompleteness in our protocluster sample. This high value suggests that protoclusters make a nonnegligible contribution to the cosmic SFRD at z ∼ 4, as previously suggested by simulations. Our results suggest that protoclusters are essential components for galaxy evolution at z ∼ 4.
Abstract
Cosmic variance introduces significant uncertainties into galaxy number density properties when surveying the high-redshift Universe with a small volume. Such uncertainties produce the ...field-to-field variance
σ
g
of galaxy numbers in observational astronomy, which significantly affects the luminosity function (LF) measurement of Ly
α
emitters (LAEs). For most previous Ly
α
LF studies,
σ
g
is often adopted from predictions by cosmological simulations, but barely confirmed by observations. Measuring cosmic variance requires a huge sample over a large volume, exceeding the capabilities of most astronomical instruments. In this study, we demonstrate an observational approach for measuring the cosmic variance contribution for
z
≈ 2.2 Ly
α
LFs. The LAE candidates are observed using the narrow band and broad band of the Subaru/Hyper Suprime-Cam in eight independent fields, making the total survey area ≃11.62 deg
2
and a comoving volume of ≃8.71 × 10
6
Mpc
3
. We report a best-fit Schechter function with parameters
α
= −1.75 (fixed),
L
Ly
α
*
=
5.95
−
0.96
+
1.22
×
10
42
erg s
−1
, and
ϕ
Ly
α
*
=
5.26
−
1.27
+
1.65
× 10
−4
Mpc
−3
for the overall Ly
α
LFs. After clipping out the regions that may bias the cosmic variance measurements, we calculate
σ
g
by sampling LAEs within multiple pointings on the field image. We investigate the relation between
σ
g
and survey volume
V
, and fit a simple power-law
σ
g
=
k
×
V
10
5
Mpc
3
β
. We find best-fit values of
−
1.399
−
0.156
+
0.160
for
β
and
1.249
−
0.193
+
0.213
for
k
. We compare our measurements with predictions from simulations and find that the cosmic variance of LAEs is likely larger than that of general star-forming galaxies.
We have carried out deep and wide field imaging observations with narrow bands, targeting 11 quasar fields to systematically study the possible photoevaporation effect of quasar radiation on ...surrounding low mass galaxies at z ∼ 2-3. We focused on Ly emitters (LAEs) at the same redshifts as quasars that lie within the quasar proximity zones, where the UV radiation from the quasars is higher than the average background at that epoch. We found that LAEs with high rest-frame equivalent width of Ly emission (EW0) of 150 with low stellar mass ( 108 M ) are predominantly scarce in the quasar proximity zones, suggesting that quasar photoevaporation effects may be taking place. The halo mass of LAEs with EW0 > 150 is estimated to be either from spectral energy distribution fitting or the main sequence. Based on a hydrodynamical simulation, the predicted delay in star formation under a local UV background intensity with erg s−1 cm−2 Hz−1 sr−1 for galaxies having less than this halo mass is about >20 Myr, which is longer than the expected age of LAEs with EW0 > 150 . On the other hand, photoevaporation seems to be less effective around very luminous quasars, which is consistent with the idea that these are still in an early stage of activity.
Abstract
We present a new catalog of 9318 Ly
α
emitter (LAE) candidates at
z
= 2.2, 3.3, 4.9, 5.7, 6.6, and 7.0 that are photometrically selected by the SILVERRUSH program with a machine learning ...technique from large area (up to 25.0 deg
2
) imaging data with six narrowband filters taken by the Subaru Strategic Program with Hyper Suprime-Cam and a Subaru intensive program, Cosmic HydrOgen Reionization Unveiled with Subaru. We construct a convolutional neural network that distinguishes between real LAEs and contaminants with a completeness of 94% and a contamination rate of 1%, enabling us to efficiently remove contaminants from the photometrically selected LAE candidates. We confirm that our LAE catalogs include 177 LAEs that have been spectroscopically identified in our SILVERRUSH programs and previous studies, ensuring the validity of our machine learning selection. In addition, we find that the object-matching rates between our LAE catalogs and our previous results are ≃80%–100% at bright NB magnitudes of ≲24 mag. We also confirm that the surface number densities of our LAE candidates are consistent with previous results. Our LAE catalogs will be made public on our project webpage.
We present measurements of the size of the quasar proximity zone (Rp) for 11 low-luminosity ( ) quasars at z ∼ 6, discovered by the Subaru High-z Exploration of Low-Luminosity Quasars project. Our ...faint quasar sample expands the Rp measurement down to mag, where more common quasar populations dominate at the epoch. We restrict the sample to quasars whose systemic redshifts have been precisely measured by C ii 158 m or Mg ii λ2798 emission lines. We also update the Rp measurements for 26 luminous quasars presented in Eilers et al. by using the latest systemic redshift results. The luminosity dependence on Rp is found to be consistent with the theoretical prediction assuming a highly ionized intergalactic medium. We find a shallow redshift evolution of the luminosity-corrected Rp, ( ) over . This trend is steeper than that of Eilers et al., but significantly shallower than those of the earlier studies. Our results suggest that Rp,corr is insensitive to the neutral fraction of the universe at z ∼ 6. Four quasars show exceptionally small ( proper Mpc), which could be the result of their young age (<104 yr) in the reionization epoch, though statistics on this are still scarce.
We present the results of a survey of the brightest UV-selected galaxies in protoclusters. These proto-brightest cluster galaxy (proto-BCG) candidates are drawn from 179 overdense regions of ...g-dropout galaxies at z ∼ 4 from the Hyper Suprime-Cam Subaru Strategic Program identified previously as good protocluster candidates. This study is the first to extend the systematic study of the progenitors of BCGs from z ∼ 2 to z ∼ 4. We carefully remove possible contaminants from foreground galaxies and, for each structure, select the brightest galaxy that is at least 1 mag brighter than the fifth-brightest galaxy. We select 63 proto-BCG candidates and compare their properties with those of galaxies in the field and those of other galaxies in overdense structures. The proto-BCG candidates and their surrounding galaxies have different rest-UV color (i − z) distributions to field galaxies and other galaxies in protoclusters that do not host proto-BCGs. In addition, galaxies surrounding proto-BCGs are brighter than those in protoclusters without proto-BCGs. The image stacking analysis reveals that the average effective radius of proto-BCGs is ∼28% larger than that of field galaxies. The i − z color differences suggest that proto-BCGs and their surrounding galaxies are dustier than other galaxies at z ∼ 4. These results suggest that specific environmental effects or assembly biases have already emerged in some protoclusters as early as z ∼ 4, and we suggest that proto-BCGs have different star formation histories than other galaxies in the same epoch.
Abstract
We present 20,567 Ly
α
emitters (LAEs) at
z
= 2.2 − 7.3 that are photometrically identified by the SILVERRUSH program in a large survey area up to 25 deg
2
with deep images of five broadband ...filters (
grizy
) and seven narrowband filters targeting Ly
α
lines at
z
= 2.2, 3.3, 4.9, 5.7, 6.6, 7.0, and 7.3 taken by the Hyper Suprime-Cam Subaru Strategic Program and the Cosmic HydrOgen Reionization Unveiled with Subaru survey. We select secure >5
σ
sources showing narrowband color excesses via Ly
α
break screening, taking into account the spatial inhomogeneity of limiting magnitudes. After removing spurious sources by careful masking and visual inspection of coadded and multiepoch images obtained over the 7 yr of the surveys, we construct LAE samples consisting of 6995, 4641, 726, 6124, 2058, 18, and 5 LAEs at
z
= 2.2, 3.3, 4.9, 5.7, 6.6, 7.0, and 7.3, respectively, although the
z
= 7.3 candidates are tentative. Our LAE catalogs contain 289 spectroscopically confirmed LAEs at the expected redshifts from previous work. We demonstrate that the number counts of our LAEs are consistent with previous studies with similar LAE selection criteria. The LAE catalogs will be made public on our project webpage with detailed descriptions of the content and ancillary information about the masks and limiting magnitudes.
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