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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 Lyα 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 Lyα width may suggest a significant contribution from the host galaxies. Thus, these objects may be composites of quasars and star-forming galaxies. [ABSTRACT FROM AUTHOR]

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 109.3M⊙. The Eddington ratios Lbol/LEdd range from 0.16 to 1.1, but the majority of the HSC quasars are powered by MBH ∼ 109M⊙ 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 ∼ 109M⊙ 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. [ABSTRACT FROM AUTHOR]

We report on the optical properties of infrared (IR)-bright dust-obscured galaxies (DOGs) that are defined as . Because supermassive black holes (SMBHs) in IR-bright DOGs are expected to be rapidly growing in the major-merger scenario, they provide useful clues for understanding the coevolution of SMBHs and their host galaxies. However, the optical properties of IR-bright DOGs remain unclear because the optical emission of a DOG is very faint. By combining ∼105 deg2 images of the optical, near-IR, and mid-IR data obtained from the Subaru Hyper Suprime-Cam (HSC) survey, the VISTA VIKING survey, and the Wide-field Infrared Survey Explorer all-sky survey, respectively, 571 IR-bright DOGs were selected. We found that IR-bright DOGs show a redder (g − z)AB color than do other populations of dusty galaxies, such as ultraluminous IR galaxies (ULIRGs) at a similar redshift, with a significantly large dispersion. Among the selected DOGs, star formation (SF)-dominated DOGs show a relatively red color, while active galactic nucleus (AGN)-dominated DOGs show a rather blue color in optical. This result is consistent with the idea that the relative AGN contribution in the optical emission becomes more significant at a later stage in the major-merger scenario. We discovered eight IR-bright DOGs showing a significant blue excess in blue HSC bands. This blue excess can be interpreted as a leaked AGN emission that is either a directly leaking or a scattered AGN emission, as proposed for some blue-excess Hot DOGs in earlier studies. [ABSTRACT FROM AUTHOR]

Using data release 1 of the Hyper Suprime-Cam Subaru Strategic Program covering about 130 square degrees at high galactic latitudes, we have obtained L dwarf counts based on the selection criteria on colors, limiting magnitude, and PSF morphology using the i, z, and y bands. Using these criteria, we have detected 3665 L dwarfs brighter than z = 24. The surface number counts obtained differentially in z magnitude are compared with predictions of an exponential disk model to estimate the thin-disk scale height in the vicinity of the Sun. In the exponential disk model, we first fix the local luminosity function (LLF) to the mean LLF of Cruz et al. and derive the best-fit scale height of 260 pc. However, this fit appears to be poor. We then allow the LLF to vary along with the scale height. We use the LLF of Cruz et al. as a starting point. The best-fit model is found for the vertical scale height of 380 pc. However, the χ2 minimum is rather broad and the 90% confidence interval is between 320 and 520 pc. We investigate another model by varying the scale height and the density of the brightest magnitude bin, while other magnitude bins are fixed to the mean LLF of Cruz et al. We find an equally good fit with the two free parameters and the best-fit scale height is again 380 pc, but the 90% confidence interval is between 340 and 420 pc. [ABSTRACT FROM AUTHOR]

We present new measurements of the quasar luminosity function (LF) at z ∼ 6 over an unprecedentedly wide range of the rest-frame ultraviolet luminosity M1450 from −30 to −22 mag. This is the fifth in a series of publications 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 Subaru Strategic Program survey. The LF was calculated with a complete sample of 110 quasars at 5.7 ≤ z ≤ 6.5, which includes 48 SHELLQs quasars discovered over 650 deg2 and 63 brighter quasars discovered by the Sloan Digital Sky Survey and the Canada–France–Hawaii Quasar Survey (including one overlapping object). This is the largest sample of z ∼ 6 quasars with a well-defined selection function constructed to date, which has allowed us to detect significant flattening of the LF at its faint end. A double power-law function fit to the sample yields a faint-end slope , a bright-end slope , a break magnitude , and a characteristic space density Gpc−3 mag−1. Integrating this best-fit model over the range −18 < M1450 < −30 mag, quasars emit ionizing photons at the rate of s−1 Mpc−3 at z = 6.0. This is less than 10% of the critical rate necessary to keep the intergalactic medium ionized, which indicates that quasars are not a major contributor to cosmic reionization. [ABSTRACT FROM AUTHOR]

We report the result of optical identifications of FIRST radio sources with the Hyper Suprime-Cam Subaru Strategic Program survey (HSC-SSP). The positional cross-match within 1″ between the FIRST and HSC-SSP catalogs (i ≲ 26) produced more than 3600 optical counterparts in the 156 deg2 of the HSC-SSP field. The matched counterparts account for more than 50% of the FIRST sources in the search field, which substantially exceed previously reported fractions of SDSS counterparts (i ≲ 22) of ∼30%. Among the matched sample, 9% are optically unresolved sources such as radio-loud quasars. The optically faint (i > 21) radio galaxies (RGs) show that the fitting linear function of the 1.4 GHz source counts has a slope that is flatter than that of the bright RGs, while optically faint radio quasars show a slope steeper than that of bright radio quasars. The optically faint RGs show a flat slope in the i-band number counts down to 24 mag, implying either less massive or distant radio-active galactic nuclei (AGNs) beyond 24 mag. The photometric redshift and the comparison of colors with the galaxy models show that most of the matched RGs are distributed at redshifts from 0 to 1.5. The optically faint sample includes the high radio-loudness sources that are not seen in the optically bright sample. Such sources are located at redshift z > 1. This study gives ∼1500 radio AGNs lying at the optically faint end and high-redshift regime not probed by previous searches. [ABSTRACT FROM AUTHOR]

Active galactic nuclei (AGNs) in the high-redshift universe are thought to reside in overdense environments. However, recent works provide controversial results, partly due to the use of different techniques and possible suppression of nearby galaxy formation by AGN feedback. We conducted deep and wide-field imaging observations with the Suprime-Cam on the Subaru Telescope and searched for Lyα emitters (LAEs) around two quasi-stellar objects (QSOs) at z ∼ 4.9 and a radio galaxy at z ∼ 4.5 by using narrowband filters to address these issues more robustly. In the QSO fields, we obtained additional broadband images to select Lyman break galaxies (LBGs) at z ∼ 5 for comparison. We constructed a photometric sample of 301 LAEs and 170 LBGs in total. A wide field of view (34′ × 27′, corresponding to 80 × 60 comoving Mpc2) of the Suprime-Cam enabled us to probe galaxies in the immediate vicinities of the AGNs and in the blank fields simultaneously and compare various properties of them in a consistent manner. The two QSOs are located near local density peaks (<2σ), and one of the QSOs has a close companion LAE with projected separation of 80 physical kpc. The radio galaxy is found to be near a void of LAEs. The number densities of LAEs/LGBs in a larger spatial scale around the AGNs are not significantly different from those in blank fields. No sign of feedback is found down to . Our results suggest that high-redshift AGNs are not associated with extreme galaxy overdensity and that this cannot be attributed to the effect of AGN feedback. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We report the discovery of 15 quasars and bright galaxies at 5.7 < z < 6.9. This is the initial result from the Subaru High-z Exploration of Low-Luminosity Quasars project, which exploits the exquisite multiband imaging data produced by the Subaru Hyper Suprime-Cam (HSC) Strategic Program survey. The candidate selection is performed by combining several photometric approaches including a Bayesian probabilistic algorithm to reject stars and dwarfs. The spectroscopic identification was carried out with the Gran Telescopio Canarias and the Subaru Telescope for the first 80 deg2 of the survey footprint. The success rate of our photometric selection is quite high, approaching 100% at the brighter magnitudes (zAB < 23.5 mag). Our selection also recovered all the known high-z quasars on the HSC images. Among the 15 discovered objects, six are likely quasars, while the other six with interstellar absorption lines and in some cases narrow emission lines are likely bright Lyman-break galaxies. The remaining three objects have weak continua and very strong and narrow Lyα lines, which may be excited by ultraviolet light from both young stars and quasars. These results indicate that we are starting to see the steep rise of the luminosity function of z ≥ 6 galaxies, compared with that of quasars, at magnitudes fainter than M1450 ∼ −22 mag or zAB ∼ 24 mag. Follow-up studies of the discovered objects as well as further survey observations are ongoing. [ABSTRACT FROM AUTHOR]

Quasar host galaxies are key for understanding the relation between galaxies and the supermassive black holes (SMBHs) at their centers. We present a study of 191 broad-line quasars and their host galaxies at using high signal-to-noise ratio (S/N) spectra produced by the Sloan Digital Sky Survey Reverberation Mapping project. Clear detection of stellar absorption lines allows a reliable decomposition of the observed spectra into nuclear and host components, using spectral models of quasar and stellar radiations as well as emission lines from the interstellar medium. We estimate age, mass , and velocity dispersion of the host stars, the star formation rate (SFR), quasar luminosity, and SMBH mass for each object. The quasars are preferentially hosted by massive galaxies with characterized by stellar ages around 1 billion yr, which coincides with the transition phase of normal galaxies from the blue cloud to the red sequence. The host galaxies have relatively low SFRs and fall below the main sequence of star-forming galaxies at similar redshifts. These facts suggest that the hosts have experienced an episode of major star formation sometime in the past 1 billion yr, which was subsequently quenched or suppressed. The derived and relations agree with our past measurements and are consistent with no evolution from the local universe. The present analysis demonstrates that reliable measurements of stellar properties of quasar host galaxies are possible with high-S/N fiber spectra, which will be acquired in large numbers with future powerful instruments such as the Subaru Prime Focus Spectrograph. [ABSTRACT FROM AUTHOR]