Hikari Shirakata

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). II. Discovery of 32 Quasars and Luminous Galaxies at 5.7 < z < 6.8

We present spectroscopic identification of 32 new quasars and luminous galaxies discovered at 5.7<z≤6.8. This is the second in a series of papers presenting the results of the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multi-band imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The photometric candidates were selected by a Bayesian probabilistic algorithm, and then observed with spectrographs on the Gran Telescopio Canarias and the Subaru Telescope. Combined with the sample presented in the previous paper, we have now identified 64 HSC sources over about 430 deg, which include 33 high-z quasars, 14 high-z luminous galaxies, 2 [O III] emitters at z ∼ 0.8, and 15 Galactic brown dwarfs. The new quasars have considerably lower luminosity (M1450 ∼−25 to −22 mag) than most of the previously known high-z quasars. Several of these quasars have luminous (> 10 erg s) and narrow (< 500 km s) Lyα lines, and also a possible mini broad absorption line system of N V λ1240 in the composite spectrum, which clearly separate them from typical quasars. On the other hand, the high-z galaxies have extremely high luminosity (M1450 ∼ −24 to −22 mag) compared to other galaxies found at similar redshift. With the discovery of these new classes of objects, we are opening up new parameter spaces in the high-z Universe. Further survey observations and follow-up studies of the identified objects, including the construction of the quasar luminosity function at z ∼ 6, are ongoing.

The impact of dust in host galaxies on quasar luminosity functions

We have investigated effects of dust attenuation on quasar luminosity functions using a semi-analytic galaxy formation model combined with a large cosmological N-body simulation. We estimate the dust attenuation of quasars self-consistently with that of galaxies by considering the dust in their host bulges. We find that the luminosity of the bright quasars is strongly dimmed by the dust attenuation, about 2 mag in the B-band. Assuming the empirical bolometric corrections for active galactic nuclei (AGNs) by Marconi et al., we find that this dust attenuation is too strong to explain the B-band and X-ray quasar luminosity functions simultaneously. We consider two possible mechanisms that weaken the dust attenuation. As such a mechanism, we introduce a time delay for AGN activity, that is, gas fueling to a central black hole starts some time after the beginning of the starburst induced by a major merger. The other is the anisotropy in the dust distribution. We find that in order to make the dust attenuation of the quasars negligible, either the gas accretion into the black holes has to be delayed at least three times the dynamical timescale of their host bulges or the dust covering factor is as small as 0.1.

Theoretical re-evaluations of the black hole mass–bulge mass relation – I. Effect of seed black hole mass

We explore the effect of varying the mass of the seed black hole on the resulting black hole mass - bulge mass relation at z ~ 0, using a semi-analytic model of galaxy formation combined with large cosmological N-body simulations. We constrain our model by requiring the observed properties of galaxies at z ~ 0 are reproduced. In keeping with previous semi-analytic models, we place a seed black hole immediately after a galaxy forms. When the mass of the seed is set at 10^5 M_sun, we find that the model results become inconsistent with recent observational results of the black hole mass - bulge mass relation for dwarf galaxies. In particular, the model predicts that bulges with ~ 10^9 M_sun harbour larger black holes than observed. On the other hand, when we employ seed black holes with 10^3 M_sun, or randomly select their mass within a 10^(3-5) M_sun range, the resulting relation is consistent with observation estimates, including the observed dispersion. We find that to obtain stronger constraints on the mass of seed black holes, observations of less massive bulges at z ~ 0 are a more powerful comparison than the relations at higher redshifts.

Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs). IV. Discovery of 41 Quasars and Luminous Galaxies at 5.7 ≤ z ≤ 6.9

We report discovery of 41 new high-z quasars and luminous galaxies, which were spectroscopically identified at 5.7 ≤ z ≤ 6.9. This is the fourth in a series of papers from the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project, based on the deep multi-band imaging data collected by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. We selected the photometric candidates by a Bayesian probabilistic algorithm, and then Corresponding author: Yoshiki Matsuoka yk.matsuoka@cosmos.ehime-u.ac.jp

Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). III. Star formation properties of the host galaxies at z ≳ 6 studied with ALMA

We present our ALMA Cycle 4 measurements of the [CII] emission line and the underlying far-infrared (FIR) continuum emission from four optically low-luminosity (

Imprints of the super-Eddington accretion on the quasar clustering

M_{\rm 1450} > -25

Theoretical Re-evaluations of Scaling Relations between SMBHs and Their Host Galaxies–2. Importance of AGN Feedback Suggested by Stellar Age–Velocity Dispersion Relation

) quasars at

Theoretical re-evaluations of scaling relations between SMBHs and their host galaxies - 1. Effect of Seed BH Mass

z \gtrsim 6

The New Numerical Galaxy Catalog (ν2GC): An updated semi-analytic model of galaxy and active galactic nucleus formation with large cosmological N-body simulations

discovered by the Subaru Hyper Suprime Cam (HSC) survey. The [CII] line and FIR continuum luminosities lie in the ranges

The New Numerical Galaxy Catalogue (\nu^2 GC): Properties of Active Galactic Nuclei and Their Host Galaxies

L_{\rm [CII]} = (3.8-10.2) \times 10^8~L_\odot