Abstract
We searched for massive galaxy population in the known large-scale high-density structure of Ly
α
emitters (LAEs) at
z
= 2.39 near the radio galaxy 53W002 by using imaging data from
B
,
V
,
...i
′
,
J
,
H
,
and
K
s
bands taken with Suprime-Cam and MOIRCS on the Subaru telescope. We selected 62 protocluster member candidates by their
JHK
s
-band colors and spectral energy distribution (SED) fitting analysis (
JHK
s
-selected galaxies) in our survey field of
70.2
arcmin
2
and compared their physical properties estimated from the SED fitting with a comparison sample in the COSMOS field. We found significant number density excesses for the
JHK
s
-selected galaxies in the 53W002 field at
K
s
< 22.25,
J
−
K
s
> 2, or
V
−
K
s
> 4. In particular, the number density of the
JHK
s
-selected galaxies with
K
s
< 22.25 and
J
−
K
s
> 2 in the 53W002 field is nine times higher than the comparison sample. Most of those with
K
s
< 22.25 and
J
−
K
s
> 2 are massive galaxies with
M
s
> 10
11
M
⊙
, and their specific star formation rates (sSFRs) of 10
−11
–10
−10
yr
−1
suggest that the star formation has not yet stopped completely. We also found a density excess of quiescent galaxies with
M
s
= 5 × 10
10
M
⊙
to 10
11
M
⊙
and sSFR < 10
−11
yr
−1
, as well as that of low-mass galaxies with
M
s
= 10
9.75
–10
10
M
⊙
and various sSFRs. The massive galaxies with
M
s
> 10
11
M
⊙
are not located at the density peaks of LAEs but widely distributed along a similar direction to the structure of LAEs over ∼15–20 comoving Mpc. On the other hand, the quiescent galaxies with sSFR < 10
−11
yr
−1
clearly avoid the structure of LAEs. Our results suggest that massive galaxies also exist in this protocluster discovered by the moderate overdensity of LAEs and their star formation activities depend on location in the protocluster.
Abstract
We report a massive quiescent galaxy at
z
spec
=
3.0922
−
0.004
+
0.008
spectroscopically confirmed at a protocluster in the SSA22 field by detecting the Balmer and Ca
ii
absorption features ...with the multi-object spectrometer for infrared exploration on the Keck I telescope. This is the most distant quiescent galaxy confirmed in a protocluster to date. We fit the optical to mid-infrared photometry and spectrum simultaneously with spectral energy distribution (SED) models of parametric and nonparametric star formation histories (SFHs). Both models fit the observed SED well and confirm that this object is a massive quiescent galaxy with a stellar mass of
log
(
M
⋆
/
M
⊙
)
=
11.26
−
0.04
+
0.03
and
11.54
−
0.00
+
0.03
, and a star formation rate of SFR/
M
⊙
yr
−1
< 0.3 and
=
0.01
−
0.01
+
0.03
for parametric and nonparametric models, respectively. The SFH from the former modeling is described as an instantaneous starburst whereas that of the latter modeling is longer-lived, but both models agree with a sudden quenching of the star formation at ∼0.6 Gyr ago. This massive quiescent galaxy is confirmed in an extremely dense group of galaxies predicted as a progenitor of a brightest cluster galaxy formed via multiple mergers in cosmological numerical simulations. We discover three new plausible O
iii
λ
5007 emitters at 3.0791 ≤
z
spec
≤ 3.0833 serendipitously detected around the target. Two of them just between the target and its nearest massive galaxy are possible evidence of their interactions. They suggest the future great size and stellar mass evolution of this massive quiescent galaxy via mergers.
Using the HST/ACS IF814W-band data, we investigated the distribution of apparent axial ratios of ∼21,000 galaxies with MV < −20 at 0.2 < z < 1.0 in the COSMOS field as a function of stellar mass, ...specific star formation rate (sSFR), and redshift. We statistically estimated intrinsic 3D shapes of these galaxies by fitting the axial-ratio distribution with triaxial ellipsoid models characterized by face-on (middle-to-long) and edge-on (short-to-long) axial ratios B/A and C/A. We found that the transition from thin disk to thick spheroid occurs at ΔMS ∼ −1 dex, i.e., 10 times lower sSFR than that of the main sequence for galaxies with Mstar = 1010-1011 M at 0.2 < z < 1.0. Furthermore, the intrinsic thickness (C/A) of passively evolving galaxies with Mstar = 1010-1011 M significantly decreases with time from C/A ∼ 0.40-0.50 at z ∼ 0.8 to C/A ∼ 0.33-0.37 at z ∼ 0.4, while those galaxies with Mstar > 1011 M have C/A ∼ 0.5 irrespective of redshift. On the other hand, star-forming galaxies on the main sequence with 109.5-1011 M show no significant evolution in their shape at 0.2 < z < 1.0, but their thickness depends on stellar mass; more massive star-forming galaxies tend to have lower C/A (thinner shape) than low-mass ones. These results suggest that some fraction of star-forming galaxies with a thin disk, which started to appear around z ∼ 1, quench their star formation without violent morphological change, and these newly added quiescent galaxies with a relatively thin shape cause the significant evolution in the axial-ratio distribution of passively evolving galaxies with Mstar < 1011 M at z < 1.
We present physical properties of radio galaxies (RGs) with f1.4 GHz > 1 mJy discovered by Subaru Hyper Suprime-Cam (HSC) and Very Large Array Faint Images of the Radio Sky at Twenty-Centimeters ...(FIRST) survey. For 1056 FIRST RGs at 0 < z ≤ 1.7 with HSC counterparts in about 100 deg2, we compiled multi-wavelength data of optical, near-infrared (IR), mid-IR, far-IR, and radio (150 MHz). We derived their color excess (E(B − V)*), stellar mass, star formation rate (SFR), IR luminosity, the ratio of IR and radio luminosity (qIR), and radio spectral index ( radio) that are derived from the spectral energy distribution (SED) fitting with CIGALE. We also estimated Eddington ratio based on stellar mass and integration of the best-fit SEDs of active galactic nucleus (AGN) component. We found that E(B − V)*, SFR, and IR luminosity clearly depend on redshift while stellar mass, qIR, and radio do not significantly depend on redshift. Since optically faint (iAB ≥ 21.3) RGs that are newly discovered by our RG survey tend to be high redshift, they tend to not only have a large dust extinction and low stellar mass but also have high SFR and AGN luminosity, high IR luminosity, and high Eddington ratio compared with optically bright ones. The physical properties of a fraction of RGs in our sample seem to differ from a classical view of RGs with massive stellar mass, low SFR, and low Eddington ratio, demonstrating that our RG survey with HSC and FIRST provides us curious RGs among entire RG population.
We search for galaxies with a strong Balmer break (Balmer break galaxies; BBGs) at z ∼ 6 over a 0.41 deg2 effective area in the COSMOS field. Based on rich imaging data, including data obtained with ...the Atacama Large Millimeter/submillimeter Array (ALMA), three candidates are identified by their extremely red K-3.6 colors, as well as by nondetection in the X-ray, optical, far-infrared, and radio bands. The nondetection in the deep ALMA observations suggests that they are not dusty galaxies but BBGs at z ∼ 6, although contamination from active galactic nuclei at z ∼ 0 cannot be completely ruled out for the moment. Our spectral energy distribution analyses reveal that the BBG candidates at z ∼ 6 have stellar masses of 5 × 1010 M dominated by old stellar populations with ages of 700 Myr. Assuming that all three candidates are real BBGs at z ∼ 6, we estimate the stellar mass density to be Mpc−3. This is consistent with an extrapolation from the lower-redshift measurements. The onset of star formation in the three BBG candidates is expected to be several hundred million yr before the observed epoch of z ∼ 6. We estimate the star formation rate density (SFRD) contributed by progenitors of the BBGs to be 2.4-12 × 10−5 M yr−1 Mpc−3 at z > 14 (99.7% confidence range). Our result suggests a smooth evolution of the SFRD beyond z = 8.
Abstract
We report optical spectroscopic observations of four blue-excess dust-obscured galaxies (BluDOGs) identified by the Subaru Hyper Suprime-Cam. BluDOGs are a subclass of dust-obscured galaxies ...(DOGs; defined with the extremely red color (
i
− 22)
AB
≥ 7.0; Toba et al., showing a significant flux excess in the optical
g
and
r
bands over the power-law fits to the fluxes at the longer wavelengths. Noboriguchi et al. have suggested that BluDOGs may correspond to the blowing-out phase involved in a gas-rich major-merger scenario. However, the detailed properties of BluDOGs are not understood because of the lack of spectroscopic information. In this work, we carry out deep optical spectroscopic observations of four BluDOGs using Subaru/FOCAS and VLT/FORS2. The obtained spectra show broad emission lines with extremely large equivalent widths, and a blue wing in the C
iv
line profile. The redshifts are between 2.2 and 3.3. The averaged rest-frame equivalent widths of the C
iv
lines are 160 ± 33 Å, ∼7 times higher than the average of a typical type 1 quasar. The FWHMs of their velocity profiles are between 1990 and 4470 km s
−1
, and their asymmetric parameters are 0.05 and 0.25. Such strong C
iv
lines significantly affect the broadband magnitudes, which are partly the origin of the blue excess seen in the spectral energy distribution of BluDOGs. Their estimated supermassive black hole masses are 1.1 × 10
8
<
M
BH
/
M
⊙
<5.5 × 10
8
. The inferred Eddington ratios of the BluDOGs are higher than 1 (1.1 <
λ
Edd
< 3.8), suggesting that the BluDOGs are in a rapidly evolving phase of supermassive black holes.
We report a discovery of a z = 4.72 radio galaxy, HSC J083913.17+011308.1, using the Lyman break technique with the Hyper Suprime-Cam Subaru Strategic Survey (HSC-SSP) catalog for Very Large Array ...Faint Images of the Radio Sky at Twenty centimeter radio sources. The number of known high-z radio galaxies (HzRGs) at z > 3 is quite small to constrain the evolution of HzRGs so far. The deep and wide-area optical survey by HSC-SSP enables us to apply the Lyman break technique to a large search for HzRGs. For an HzRG candidate among pre-selected r-band dropouts with a radio detection, a follow-up optical spectroscopy with the Gemini Multi-Object Spectrographs (GMOS)/Gemini has been performed. The obtained spectrum presents a clear Ly emission line redshifted to z = 4.72. The spectral energy distribution fitting analysis with the rest-frame UV and optical photometries suggests the massive nature of this HzRG with . The small equivalent width of Ly and the moderately red UV colors indicate its dusty host galaxy, implying a chemically evolved and dusty system. The radio spectral index does not meet a criterion for an ultra-steep spectrum, of −1.1 and of −0.9, demonstrating that the HSC-SSP survey compensates for a subpopulation of HzRGs that are missed in surveys focusing on an ultra-steep spectral index.
We present a study of the gas kinematics of star-forming galaxies associated with protocluster 4C 23.56 at z = 2.49 using 0 4 resolution CO (4-3) data taken with ALMA. Eleven H emitters (HAEs) are ...detected in CO (4-3), including six HAEs that were previously detected in CO (3-2) at a coarser angular resolution. The detections in both CO lines are broadly consistent in the line widths and the redshifts, confirming both detections. With an increase in the number of spectroscopic redshifts, we confirm that the protocluster is composed of two merging groups with a total halo mass of log (Mcl/M ) = 13.4-13.6, suggesting that the protocluster would evolve into a Virgo-like cluster (>1014 M ). We compare the CO line widths and the CO luminosities with other (proto)clusters (ngal = 91) and general field (ngal = 80) galaxies from other studies. The 4C 23.56 protocluster galaxies have CO line widths and luminosities comparable to other protocluster galaxies on average. On the other hand, the CO line widths are on average broader by 50% compared to field galaxies, while the median CO luminosities are similar. The broader line widths can be attributed to both effects of unresolved gas-rich mergers and/or compact gas distribution, which is supported by our limited but decent angular resolution observations and the size estimate of three galaxies. Based on these results, we argue that gas-rich mergers may play a role in the retention of the specific angular momentum to a value similar to that of field populations during cluster assembly, though we need to verify this with a larger number of samples.
ABSTRACT We present measurements of the clustering properties of a sample of infrared (IR) bright dust-obscured galaxies (DOGs). Combining 125 deg2 of wide and deep optical images obtained with the ...Hyper Suprime-Cam on the Subaru Telescope and all-sky mid-IR images taken with Wide-Field Infrared Survey Explorer, we have discovered 4367 IR-bright DOGs with and flux density at 22 mJy. We calculate the angular autocorrelation function (ACF) for a uniform subsample of 1411 DOGs with 3.0 mJy < flux (22 ) < 5.0 mJy and < 24.0. The ACF of our DOG subsample is well-fit with a single power law, = (0.010 0.003) , where θ is in degrees. The correlation amplitude of IR-bright DOGs is larger than that of IR-faint DOGs, which reflects a flux dependence of the DOG clustering, as suggested by Brodwin et al. We assume that the redshift distribution for our DOG sample is Gaussian, and consider two cases: (1) the redshift distribution is the same as IR-faint DOGs with flux at 22 < 1.0 mJy, mean and sigma z = 1.99 0.45, and (2) z = 1.19 0.30, as inferred from their photometric redshifts. The inferred correlation length of IR-bright DOGs is r0 = 12.0 2.0 and 10.3 1.7 Mpc, respectively. IR-bright DOGs reside in massive dark matter halos with a mass of and in the two cases, respectively.
We present deep
$J$
-,
$H$
-, and
$K_{\rm s}$
-band imaging data of the MOIRCS Deep Survey (MODS), which was carried out with the Multi-Object Infrared Camera and Spectrograph (MOIRCS) mounted on the ...Subaru Telescope in the GOODS-North region. The data reach 5
$\ \sigma$
total limiting magnitudes for point sources of
$J$
$=$
23.9,
$H$
$=$
22.8, and
$K_{\rm s}$
$=$
22.8 (Vega magnitude) over 103 arcmin
$^{2}$
(wide field). In 28 arcmin
$^{2}$
of the survey area, which is an ultra-deep field of the MODS (deep field), the data reach 5
$\ \sigma$
depths of
$J$
$=$
24.8,
$H$
$=$
23.4, and
$K_{\rm s}$
$=$
23.8. The spatial resolutions of the combined images are FWHM
$\sim\ $
0
$''\!\!\!.$
6 and
$\sim\ $
0
$''\!\!\!.$
5 for the wide and deep fields in all bands, respectively. Combining the MODS data with the multi-wavelength public data taken with the HST, Spitzer, and other ground-based telescopes in the GOODS field, we constructed a multi-wavelength photometric catalog of
$K_{\rm s}$
-selected sources. Using the catalog, we present
$K_{\rm s}$
-band number counts and near-infrared color distribution of the detected objects; we also demonstrate some selection techniques with the NIR colors for high redshift galaxies. These data and catalog are publicly available via Internet.
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