We present deep near-infrared spectroscopy of six quasars at 6.1 ≤ z ≤ 6.7 with Very Large Telescope/X-Shooter and Gemini-N/GNIRS. Our objects, originally discovered through a wide-field optical ...survey with the Hyper Suprime-Cam (HSC) Subaru Strategic Program (HSC-SSP), have the lowest luminosities (−25.5 mag ≤ M1450 ≤ −23.1 mag) of the z > 5.8 quasars with measured black hole (BH) masses. From single-epoch mass measurements based on Mg ii λ2798, we find a wide range in BH masses, from MBH = 107.6 to 109.3 M . The Eddington ratios Lbol/LEdd range from 0.16 to 1.1, but the majority of the HSC quasars are powered by MBH ∼ 109 M supermassive black holes (SMBHs) accreting at sub-Eddington rates. The Eddington ratio distribution of the HSC quasars is inclined to lower accretion rates than those of Willott et al., who measured the BH masses for similarly faint z ∼ 6 quasars. This suggests that the global Eddington ratio distribution is wider than has previously been thought. The presence of MBH ∼ 109 M SMBHs at z ∼ 6 cannot be explained with constant sub-Eddington accretion from stellar remnant seed BHs. Therefore, we may be witnessing the first buildup of the most massive BHs in the first billion years of the universe, the accretion activity of which is transforming from active growth to a quiescent phase. Measurements of a larger complete sample of z 6 low-luminosity quasars, as well as deeper observations with future facilities, will enable us to better understand the early SMBH growth in the reionization epoch.
We report the discovery of 28 quasars and 7 luminous galaxies at 5.7 ≤ z ≤ 7.0. This is the tenth in a series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, ...which exploits the deep multiband imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The total number of spectroscopically identified objects in SHELLQs has now grown to 93 high-z quasars, 31 high-z luminous galaxies, 16 O iii emitters at z ∼ 0.8, and 65 Galactic cool dwarfs (low-mass stars and brown dwarfs). These objects were found over 900 deg2, surveyed by HSC between 2014 March and 2018 January. The full quasar sample includes 18 objects with very strong and narrow Ly emission, whose stacked spectrum is clearly different from that of other quasars or galaxies. While the stacked spectrum shows N v λ1240 emission and resembles that of lower-z narrow-line quasars, the small Ly width may suggest a significant contribution from the host galaxies. Thus, these objects may be composites of quasars and star-forming galaxies.
We report the discovery of a quasar at z = 7.07, which was selected from the deep multi-band imaging data collected by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. This quasar, HSC ...J124353.93+010038.5, has an order of magnitude lower luminosity than do the other known quasars at z > 7. The rest-frame ultraviolet absolute magnitude is M1450 = −24.13 0.08 mag and the bolometric luminosity is erg s−1. Its spectrum in the optical to near-infrared shows strong emission lines, and shows evidence for a fast gas outflow, as the C iv line is blueshifted and there is indication of broad absorption lines. The Mg ii-based black hole mass is , thus indicating a moderate mass accretion rate with an Eddington ratio . It is the first z > 7 quasar with sub-Eddington accretion, besides being the third most distant quasar known to date. The luminosity and black hole mass are comparable to, or even lower than, those measured for the majority of low-z quasars discovered by the Sloan Digital Sky Survey, and thus this quasar likely represents a z > 7 counterpart to quasars commonly observed in the low-z universe.
Abstract
Spatially compact objects with extremely red color in the rest-frame optical to near-infrared (0.4–1
μ
m) and blue color in the rest-frame ultraviolet (UV; 0.2–0.4
μ
m) have been discovered ...at 5 <
z
< 9 using the James Webb Space Telescope (JWST). These extremely red objects (JWST-EROs) exhibit spectral energy distributions (SEDs) that are difficult to explain using a single component of either star-forming galaxies or quasars, leading to two-component models in which the blue UV and extremely red optical are explained using less-dusty and dusty spectra of galaxies or quasars, respectively. Here, we report the remarkable similarity in SEDs between JWST-EROs and blue-excess dust-obscured galaxies (BluDOGs) identified at 2 <
z
< 3. BluDOGs are a population of active galactic nuclei (AGNs) with black hole masses of ∼10
8–9
M
⊙
, which are 1 order of magnitude larger than those in some JWST-EROs. The Eddington ratios of BluDOGs are 1 or higher, whereas those of JWST-EROs are in the range of 0.1–1. Therefore, JWST-EROs are less massive, less active, and more common counterparts in higher-
z
of BluDOGs in cosmic noon. Conversely, JWST-EROs have a significantly higher fraction of those with blue excess than DOGs. We present the average UV spectra of BluDOGs as a comparison to JWST-EROs and discuss a coherent evolutionary scenario for dusty AGN populations.
Abstract
We report the distribution of black hole (BH) masses and Eddingont ratios estimated for a sample of 131 low luminosity quasars in the early cosmic epoch (5.6 <
z
< 7.0). Our work is based on ...the Subaru High-
z
Exploration of Low-Luminosity Quasars (SHELLQs) project, which has constructed a low luminosity quasar sample down to
M
1450
∼ − 21 mag, exploiting the survey data of Hyper Suprime-Cam installed on Subaru Telescope. The discovery spectra of these quasars are limited to the rest-frame wavelengths of ∼1200–1400 Å, which contain no emission lines that can be used as BH mass estimators. In order to overcome this problem, we made use of low-
z
counterpart spectra from the Sloan Digital Sky Survey, which are spectrally matched to the high-
z
spectra in overlapping wavelengths. We then combined the C
iv
emission line widths of the counterparts with the continuum luminosity from the SHELLQs data to estimate BH masses. The resulting BH mass distribution has a range of ∼10
7–10
M
⊙
, with most of the quasars having BH masses ∼10
8
M
⊙
with sub-Eddington accretion. The present study provides not only a new insight into normal quasars in the reionization epoch, but also a new promising way to estimate BH masses of high-
z
quasars without near-infrared spectroscopy.
Abstract
We aim to determine why there exists anisotropic H
i
absorption around quasars; i.e., the environments around quasars are highly biased toward producing strong H
i
absorption in the ...transverse direction while there exists a significant deficit of H
i
absorption within a few megaparsecs of quasars along the line of sight. The most plausible explanation for this opposite trend is that the transverse direction is shielded from quasar UV radiation by dust torus. However, a critical weakness of this explanation is that we do not have any information on the inclination angle of our sightline relative to the torus. In this study, we examine environments of quasars with broad-absorption troughs in their spectra (i.e., BAL quasars) because it is widely believed that BAL troughs are observed if the central continuum is viewed from the side through their powerful outflows near the dust torus. With closely separated 12 projected quasar pairs at different redshifts with a separation angle of
θ
< 120″, we examine H
i
absorption at foreground BAL quasars in the spectra of background quasars. We confirm that there exists optically thick gas around two of 12 BAL quasars, and that the mean H
i
absorption strength is EW
rest
∼ 1 Å. This is consistent with past results of studies of non-BAL quasars, although not statistically significant. The origins of optically thick H
i
absorbers around BAL and non-BAL quasars could be different since their column densities are different by ∼3 orders of magnitude. A larger sample is required to narrow down possible scenarios explaining the anisotropic H
i
absorption around quasars.
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.
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.
Abstract
Active galactic nuclei (AGNs) are key in understanding the coevolution of galaxies and supermassive black holes (SMBHs). AGN activity is thought to affect the properties of their host ...galaxies via a process called “AGN feedback,” which drives the coevolution. From a parent sample of 1151 z < 1 type-1 quasars from the Sloan Digital Sky Survey quasar catalog, we detected the host galaxies of 862 of them in the high-quality grizy images of the Subaru Hyper Suprime-Cam survey. The unprecedented combination of the survey area and depth allowed us to perform a statistical analysis of the quasar host galaxies, with small sample variance. We fitted the radial image profile of each quasar as a linear combination of the point spread function and the Sérsic function, decomposing the images into the quasar nucleus and the host galaxy components. We found that the host galaxies are massive, with stellar mass Mstar ≳ 1010 $M_\odot$, and are mainly located on the green valley. This trend is consistent with a scenario in which star formation in the host galaxies is suppressed by AGN feedback, that is, AGN activity may be responsible for the transition of these galaxies from the blue cloud to the red sequence. We also investigated the SMBH mass to stellar mass relation of the z < 1 quasars, and found a consistent slope with the local relation, while the SMBHs may be slightly undermassive. However, the above results are subject to our sample selection, which biases against host galaxies with low masses and/or large quasar-to-host flux ratios.
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.
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