Abstract
The early evolution of the quasar luminosity function (QLF) and black hole mass function (BHMF) encodes key information on the physics determining the radiative and accretion processes of ...supermassive black holes (BHs) in high-
z
quasars. Although the QLF shape has been constrained by recent observations, it remains challenging to develop a theoretical model that explains its redshift evolution associated with BH growth self-consistently. In this study, based on a semianalytical model for the BH formation and growth, we construct the QLF and BHMF of the early BH population that experiences multiple accretion bursts, in each of which a constant Eddington ratio is assigned following a Schechter distribution function. Our best-fit model to reproduce the observed QLF and BHMF at
z
≃ 6 suggests that several episodes of moderate super-Eddington accretion occur and each of them lasts for
τ
≃ 20–30 Myr. The average duty cycle in super-Eddington phases is ≃15% for massive BHs that reach ≳10
8
M
⊙
by
z
≃ 6, which is nearly twice that of the entire population. We find that the observed Eddington ratio distribution function is skewed to a lognormal shape owing to detection limits of quasar surveys. The predicted redshift evolution of the QLF and BHMF suggests a rapid decay of their number and mass density in a cosmic volume toward
z
≳ 6. These results will be unveiled by future deep and wide surveys with the James Webb Space Telescope, Roman Space Telescope, and Euclid.
Abstract
We study the early growth of massive seed black holes (BHs) via accretion in protogalactic nuclei where the stellar bulge component is assembled, performing axisymmetric two-dimensional ...radiation hydrodynamical simulations. We find that when a seed BH with
M
•
∼ 10
5
M
⊙
is embedded in dense metal-poor gas (
Z
= 0.01
Z
⊙
) with a density of ≳ 100 cm
−3
and bulge stars with a total mass of
M
⋆
≳ 100
M
•
, a massive gaseous disk feeds the BH efficiently at rates of ≳ 0.3–1
M
⊙
yr
−1
, and the BH mass increases nearly tenfold within ∼2 Myr. This rapid accretion phase lasts until a good fraction of the gas bounded within the bulge accretes onto the BH, although the feeding rate is regulated owing to strong outflows driven by ionizing radiation emitted from the accreting BH. The transient growing mode can be triggered for seed BHs formed in massive dark-matter halos with masses of ≳ 10
9
M
⊙
at
z
∼ 15–20 (the virial temperature is
T
vir
≃ 10
5
K). The host halos are heavier and rarer than those of typical first galaxies, but are more likely to end up in quasar hosts by
z
≃ 6. This mechanism naturally yields a mass ratio of
M
•
/
M
⋆
> 0.01 higher than the value seen in the local universe. The existence of such overmassive BHs provides us with a unique opportunity to detect highly accreting seed BHs at
z
∼ 15 with AB magnitude of
m
AB
∼ 26–29 mag at 2
μ
m (rest frame 10 eV) by the upcoming observations by the James Webb Space Telescope and Nancy Grace Roman Space Telescope.
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.
Abstract
We report on the discovery of two low-luminosity, broad-line active galactic nuclei (AGNs) at
z
> 5 identified using JWST NIRSpec spectroscopy from the Cosmic Evolution Early Release Science ...(CEERS) survey. We detect broad H
α
emission in the spectra of both sources, with FWHM of 2060 ± 290 km s
−1
and 1800 ± 200 km s
−1
, resulting in virial black hole (BH) masses that are 1–2 dex below those of existing samples of luminous quasars at
z
> 5. The first source, CEERS 2782 at
z
= 5.242, is 2–3 dex fainter than known quasars at similar redshifts and was previously identified as a candidate low-luminosity AGN based on its morphology and rest-frame optical spectral energy distribution (SED). We measure a BH mass of
M
BH
= (1.3 ± 0.4) × 10
7
M
⊙
, confirming that this AGN is powered by the least massive BH known in the Universe at the end of cosmic reionization. The second source, CEERS 746 at
z
= 5.624, is inferred to be a heavily obscured, broad-line AGN caught in a transition phase between a dust-obscured starburst and an unobscured quasar. We estimate its BH mass to be in the range of
M
BH
≃ (0.9–4.7) × 10
7
M
⊙
, depending on the level of dust obscuration assumed. We perform SED fitting to derive host stellar masses,
M
⋆
, allowing us to place constraints on the BH–galaxy mass relationship in the lowest mass range yet probed in the early Universe. The
M
BH
/
M
⋆
ratio for CEERS 2782, in particular, is consistent with or higher than the empirical relationship seen in massive galaxies at
z
= 0. We examine the narrow emission line ratios of both sources and find that their location on the BPT and OHNO diagrams is consistent with model predictions for moderately low metallicity AGNs with
Z
/
Z
⊙
≃ 0.2–0.4. The spectroscopic identification of low-luminosity, broad-line AGNs at
z
> 5 with
M
BH
≃ 10
7
M
⊙
demonstrates the capability of JWST to push BH masses closer to the range predicted for the BH seed population and provides a unique opportunity to study the early stages of BH–galaxy assembly.
Abstract The James Webb Space Telescope (JWST) has recently uncovered the presence of low-luminosity active galactic nuclei (AGNs) at z = 4–11. Spectroscopic observations have provided estimates of ...the nuclear black hole (BH) masses for these sources, extending the low-mass boundary down to M • ∼ 10 6–7 M ⊙ . Despite this breakthrough, the observed lowest mass of BHs is still ≳1–2 orders of magnitude heavier than the predicted mass range of their seed population, thereby leaving the initial mass distribution of massive BHs poorly constrained. In this paper, we focus on UV-to-optical (in the rest frame) flares of stellar tidal disruption events (TDEs) embedded in low-luminosity AGNs as a tool for exploring low-mass BH populations with ≲10 4–6 M ⊙ . We provide an estimate of the TDE rate over z = 4–11, associated with the properties of JWST-detected AGN host galaxies, and we find that deep and wide survey programs with JWST and the Roman Space Telescope (RST) can detect and identify TDEs up to z ≃ 4–7. The predicted detection numbers of TDEs at z > 4 in 1 yr are N TDE ∼ 2 – 10 ( 0.2 – 2 ) for the JADES-Medium (and COSMOS-Web) survey with JWST and N TDE ∼ 2 – 10 ( 8 – 50 ) for the deep (and wide) tiers of the High Latitude Time Domain Survey with RST. We further discuss survey strategies for hunting for transient high-redshift TDEs in wide-field surveys with RST, as well as a joint observation campaign with the Vera C. Rubin Observatory for enhancing the detection number. The high-redshift TDE search will give us a unique opportunity to probe the mass distribution of early BH populations.
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.
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 deg super(2) of the survey footprint. The success rate of our photometric selection is quite high, approaching 100% at the brighter magnitudes (z sub(AB)< 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 Lyalpha 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> or = 6 galaxies, compared with that of quasars, at magnitudes fainter than M sub(1450)~ -22 mag or z sub(AB)~ 24 mag. Follow-up studies of the discovered objects as well as further survey observations are ongoing.
Abstract
We report a candidate of a low-luminosity active galactic nucleus (AGN) at
z
= 5 that was selected from the first near-infrared images of the JWST CEERS project. This source, named ...CEERS-AGN-z5-1 at absolute 1450 Å magnitude
M
1450
= −19.5 ± 0.3, was found via a visual selection of compact sources from a catalog of Lyman break galaxies at
z
> 4, taking advantage of the superb spatial resolution of the JWST/NIRCam images. The 20 photometric data available from CFHT, Hubble Space Telescope, Spitzer, and JWST suggest that the continuum shape of this source is reminiscent of that for an unobscured AGN, and there is a clear color excess in the filters where the redshifted H
β
+O
iii
and H
α
are covered. The estimated line luminosity is
L
H
β
+O
III
= 10
43.0
erg s
−1
and
L
H
α
= 10
42.9
erg s
−1
with the corresponding rest-frame equivalent width EW
H
β
+O
III
= 1100 Å and EW
H
α
= 1600 Å, respectively. Our spectral energy distribution fitting analysis favors the scenario that this object is either a strong broad-line emitter or even a super-Eddington accreting black hole (BH), although a possibility of an extremely young galaxy with moderate dust attenuation is not completely ruled out. The bolometric luminosity,
L
bol
= 2.5 ± 0.3 × 10
44
erg s
−1
, is consistent with those of
z
< 0.35 broad-line AGNs with
M
BH
∼ 10
6
M
⊙
accreting at the Eddington limit. This new AGN population in the first 1.1 billion years of the universe may close the gap between the observed BH mass range at high redshift and that of BH seeds. Spectroscopic confirmation is awaited to secure the redshift and its AGN nature.
ABSTRACT We present the discovery of three protoclusters at z ∼ 3-4 with spectroscopic confirmation in the Canada-France-Hawaii Telescope Legacy Survey Deep Fields. In these fields, we investigate ...the large-scale projected sky distribution of z ∼ 3-6 Lyman-break galaxies and identify 21 protocluster candidates from regions that are overdense at more than 4 overdensity significance. Based on cosmological simulations, it is expected that more than 76% of these candidates will evolve into a galaxy cluster of at least a halo mass of 1014 M at z = 0. We perform follow-up spectroscopy for eight of the candidates using Subaru/FOCAS, Keck II/DEIMOS, and Gemini-N/GMOS. In total we target 462 dropout candidates and obtain 138 spectroscopic redshifts. We confirm three real protoclusters at z = 3-4 with more than five members spectroscopically identified and find one to be an incidental overdense region by mere chance alignment. The other four candidate regions at z ∼ 5-6 require more spectroscopic follow-up in order to be conclusive. A z = 3.67 protocluster, which has 11 spectroscopically confirmed members, shows a remarkable core-like structure composed of a central small region (<0.5 physical Mpc) and an outskirts region (∼1.0 physical Mpc). The Ly equivalent widths of members of the protocluster are significantly smaller than those of field galaxies at the same redshift, while there is no difference in the UV luminosity distributions. These results imply that some environmental effects start operating as early as at z ∼ 4 along with the growth of the protocluster structure. This study provides an important benchmark for our analysis of protoclusters in the upcoming Subaru/HSC imaging survey and its spectroscopic follow-up with the Subaru/PFS that will detect thousands of protoclusters up to z ∼ 6.
PDF
