arXiv subjects

Nozomu Kawakatu

Publications and source records attributed to Nozomu Kawakatu.

At least 37 records · Page 2Linked to original sources

arXiv2020

ALMA 0.02"-resolution observations reveal HCN-abundance-enhanced counter-rotating and outflowing dense molecular gas at the NGC 1068 nucleus

We present ALMA ~0.02"-resolution observations of the nucleus of the nearby (~14 Mpc) type-2 AGN NGC 1068 at HCN/HCO+/HNC J=3-2 lines, as well as at their 13C isotopologue and vibrationally excited lines, to scrutinize the morphological/dynamical/chemical/physical properties of dense molecular gas in the putative dusty molecular torus around a mass-accreting supermassive black hole. We confirm almost east-west-oriented dense molecular gas emission both morphologically and dynamically, which we regard as coming from the torus. Bright emission is compact (<3 pc), and low-surface-brightness emission extends out to 5-7 pc. These dense molecular gas properties are not symmetric between the eastern and western torus. The HCN J=3-2 emission is stronger than the HCO+ J=3-2 emission within the ~7 pc torus region, with an estimated dense molecular mass of (0.4-1.0)x10^6Msun. We interpret that HCN abundance is enhanced in the torus. We detect signatures of outflowing dense molecular gas and a vibrationally excited HCN J=3-2 line. Finally, we find that in the innermost (<1 pc) part of the torus, the dense molecular line rotation velocity, relative to the systemic velocity, is the opposite of that in the outer (>2 pc) part, in both the eastern and western torus. We prefer a scenario of counter-rotating dense molecular gas with innermost almost-Keplerian-rotation and outer slowly rotating (far below Keplerian) components. Our high-spatial-resolution dense molecular line data reveal that torus properties of NGC 1068 are much more complicated than the simple axi-symmetrically rotating torus picture in the classical AGN unification paradigm.

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arXiv2020

The radio-loud narrow-line Seyfert 1 galaxy 1H 0323+342 in a galaxy merger

The supermassive black holes (SMBHs) of narrow-line Seyfert 1 galaxies (NLS1s) are at the lowest end of mass function of active galactic nuclei (AGNs) and preferentially reside in late-type host galaxies with pseudobulges, which are thought to be formed by internal secular evolution. On the other hand, the population of radio-loud NLS1s presents a challenge for the relativistic jet paradigm that powerful radio jets are exclusively associated with very high mass SMBHs in elliptical hosts, which are built-up through galaxy mergers. We investigated distorted radio structures associated with the nearest gamma-ray emitting, radio-loud NLS1 1H 0323+342. This provides supporting evidence for the merger hypothesis based on the past optical/near-infrared observations of its host galaxy. The anomalous radio morphology consists of two different structures, the inner curved structure of currently active jet and the outer linear structure of low-brightness relics. Such a coexistence might be indicative of the stage of an established black hole binary with precession before the black holes coalesce in the galaxy merger process. 1H 0323+342 and other radio-loud NLS1s under galaxy interactions may be extreme objects on the evolutionary path from radio-quiet NLS1s to normal Seyfert galaxies with larger SMBHs in classical bulges through mergers and merger-induced jet phases.

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arXiv2020

Constraints on Circumnuclear Disk through Free-Free Absorption in the Nucleus of 3C 84 with KaVA and KVN at 43 and 86 GHz

The nearby bright radio galaxy 3C 84 at the center of Perseus cluster is one of the ideal targets to explore the jet in active galactic nuclei (AGNs) and its parsec-scale environment. A recent research of Fujita & Nagai revealed the existence of the northern counter-jet component (N1) located at $\sim$ 2 mas north from the central core in VLBI images at 15 and 43 GHz and they are explained by the free-free absorption (FFA) due to an ionized plasma foreground. Here we report a new quasi-simultaneous observation of 3C 84 with the Korean VLBI Network (KVN) at 86 GHz and the KVN and VERA (VLBI Exploration of Radio Astrometry) Array (KaVA) at 43 GHz in 2016 February. We succeeded the first detection of N1 at 86 GHz and the data show that N1 still has an inverted spectrum between 43 and 86 GHz with its spectral index $α$ ($S_ν \propto ν^α$) of $1.19 \pm 0.43$, while the approaching lobe component has the steep spectrum with the index of $-0.54 \pm 0.30$. Based on the measured flux asymmetry between the counter and approaching lobes, we constrain the averaged number density of the FFA foreground $n_{\rm e}$ as $1.8 \times 10^{4}~{\rm cm^{-3}} \lesssim n_{\rm e} \lesssim 1.0 \times 10^{6}~{\rm cm^{-3}}$. Those results suggest that the observational properties of the FFA foreground can be explained by the dense ionized gas in the circumnuclear disk and/or assembly of clumpy clouds at the central $\sim 1$ pc region of 3C 84.

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arXiv2019

Obscuring fraction of active galactic nuclei implied by supernova and radiative feedbacks

We study the obscuring structure of circumnuclear disks (CNDs) by considering supernova (SN) feedbacks from nuclear starburst and the effect of anisotropic radiative pressure from AGNs. We suppose that the mass accretion onto a central supermassive black hole (SMBH) is triggered by SN-driven turbulence within CNDs, and we explore how the structures of CNDs depend on the BH mass ($M_{\rm BH}$) and AGN luminosity ($L_{\rm AGN}$). We find that the obscuring fraction ($f_{\rm obs}$) peaks at $\sim10\%$ of the Eddington luminosity ($L_{\rm Edd}$), and its maximal value is $f_\mathrm{obs} \sim 0.6$ for less massive SMBHs (e.g., $M_{\rm BH} < 10^{8}M_{\odot}$). This is because the scale height of CNDs is determined by the SN-driven accretion for a smaller $L_{\rm AGN}$, while the dusty molecular gas in CNDs is blown away by the radiation pressure from AGNs beyond the critical luminosity. On the other hand, for massive SMBHs (e.g., $M_{\rm BH} > 10^{8}M_{\odot}$), $f_{\rm obs}$ is always smaller than $0.2$, and it is almost independent of $L_{\rm AGN}$ because the scale height of CNDs is mainly controlled by the maximal star-formation efficiency ($C_{\rm *, max}$) in CNDs. By comparison with the obscuring fractions suggested from the mid-infrared observations of nearby AGNs, the SN plus radiative feedback model with $C_{\rm *, max} = 10^{-7}\, {\rm yr}^{-1}$ well reproduces the observations for $M_\mathrm{BH} = 10^8 M_\odot$. We also find that the intense starburst or the existence of dust-free absorbers inside CNDs are necessary, to explain X-ray observations.

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arXiv2019

Radio jet structures at ~100 parsec and larger scales of the $γ$-ray-emitting narrow-line Seyfert 1 galaxy PMN J0948+0022

The narrow-line Seyfert 1 (NLS1) galaxy PMN J0948+0022 is an archetype of gamma-ray-emitting NLS1s in active galactic nuclei (AGNs). In this study, we investigate its radio structures using archival data obtained using the Karl G.~Jansky very large array (VLA) and the very long baseline array (VLBA). The new VLA images reveal an outermost radio emission separated by 9.1 arcsec. Its resolved structure and steep spectrum suggest a terminal shock in a radio lobe energized by the jet from the PMN J0948+0022 nucleus. This large-scale radio component is found at almost the same position angle as that of the pc-scale jet, indicating a stable jet direction up to ~1 Mpc. Its apparent one-sidedness implies a moderate advancing speed ($β>0.27$). The kinematic age of 1 x 10^7 year of the jet activity is consistent with the expected NLS1 phase of ~10^7 year in the AGN lifetime. The VLBA image reveals the jet structure at distances ranging from r=0.82 milliarcsec to 3.5 milliarcsec, corresponding to approximately 100 pc, where superluminal motions were found. The jet width profile ($\propto r^{1.12}$) and flux-density profile ($\propto r^{-1.44}$) depending on the distance $r$ along the jet suggest that the jet kinetic energy is converted into internal energy in this region. The jet is causally connected in a nearly conical streamline, which is supported by ambient pressure at 100 pc scales in the host galaxy of PMN J0948+0022.

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arXiv2016

Do Circumnuclear Dense Gas Disks Drive Mass Accretion onto Supermassive Black Holes?

We present a positive correlation between the mass of dense molecular gas ($M_{\rm dense}$) of $\sim 100$ pc scale circumnuclear disks (CNDs) and the black hole mass accretion rate ($\dot{M}_{\rm BH}$) in total 10 Seyfert galaxies, based on data compiled from the literature and an archive (median aperture $θ_{\rm med}$ = 220 pc). A typical $M_{\rm dense}$ of CNDs is 10$^{7-8}$ $M_\odot$, estimated from the luminosity of the dense gas tracer, the HCN($1-0$) emission line. Because dense molecular gas is the site of star formation, this correlation is virtually equivalent to the one between nuclear star formation rate and $\dot{M}_{\rm BH}$ revealed previously. Moreover, the $M_{\rm dense}-\dot{M}_{\rm BH}$ correlation was tighter for CND-scale gas than for the gas on kpc or larger scales. This indicates that CNDs likely play an important role in fueling black holes, whereas $>$kpc scale gas does not. To demonstrate a possible approach for studying the CND-scale accretion process with the Atacama Large Millimeter/submillimeter Array (ALMA), we used a mass accretion model where angular momentum loss due to supernova explosions is vital. Based on the model prediction, we suggest that only the partial fraction of the mass accreted from the CND ($\dot{M}_{\rm acc}$) is consumed as $\dot{M}_{\rm BH}$. However, $\dot{M}_{\rm acc}$ agrees well with the total nuclear mass flow rate (i.e., $\dot{M}_{\rm BH}$ + outflow rate). Although these results are still tentative with large uncertainties, they support the view that star formation in CNDs can drive mass accretion onto supermassive black holes in Seyfert galaxies.

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arXiv2016

AGN Jet Power, Formation of X-ray Cavities, and FR I/II Dichotomy in Galaxy Clusters

We investigate the ability of jets in active galactic nuclei (AGNs) to break out of the ambient gas with sufficiently large advance velocities. Using observationally estimated jet power, we analyze 28 bright elliptical galaxies in nearby galaxy clusters. Because the gas density profiles in the innermost regions of galaxies have not been resolved so far, we consider two extreme cases for temperature and density profiles. We also follow two types of evolution for the jet cocoons: being driven by the pressure inside the cocoon (Fanaroff-Riley [FR] I type), and being driven by the jet momentum (FR II type). Our main result is that regardless of the assumed form of density profiles, jets with observed powers of <~ 10^{44} erg s^{-1} are not powerful enough to evolve as FR II sources. Instead, they evolve as FR I sources and appear to be decelerated below the buoyant velocities of the cocoons when jets were propagating through the central dense regions of the host galaxies. This explains the reason why FR I sources are more frequent than FR II sources in clusters. Furthermore, we predict the sizes of X-ray cavities from the observed jet powers and compare them with the observed ones --- they are consistent within a factor of two if the FR I type evolution is realized. Finally, we find that the jets with a power >~ 10^{44} erg s^{-1} are less affected by the ambient medium, and some of them, but not all, could serve as precursors of the FR II sources.

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arXiv2016

AGN jet power and feedback characterised by Bondi accretion in brightest cluster galaxies

(Abridged) We propose a new method to estimate the Bondi (hot gas) accretion rates, \dot M_B, onto the supermassive black holes (SMBHs) at the centres of elliptical galaxies. It can be applied even if the Bondi radius is not well-resolved in X-ray observations. This method is based on two simple assumptions: (1) hot gas outside the Bondi radius is in nearly a hydrostatic equilibrium, and (2) the gas temperature near the galaxy centre is close to the virial temperature. We apply this method to 28 bright elliptical galaxies in nearby galaxy clusters (27 of them are the brightest cluster galaxies; BCGs). We find a correlation between the Bondi accretion rates and the power of jets associated with the SMBHs over four orders of magnitude in \dot M_B. For most galaxies, the accretion rates are large enough to account for the jet powers. Our results indicate that the feedback from the active galactic nuclei (AGN) correlates with the properties of the hot gas surrounding the SMBHs. We also find that more massive SMBHs in BCGs tend to have larger specific growth rates. This may explain the hyper masses (~ 10^10 M_sun) of some of the SMBHs. Comparison between the accretion rates and the X-ray luminosities of the AGN suggests that the AGN in the BCGs are extremely radiatively inefficient compared with X-ray binaries in the Milky Way, even when their Eddington accretion ratio, \dot M_B/\dot M_Edd, exceeds 0.01. Lastly, we find a tight correlation between the Bondi accretion rates and the X-ray luminosities of cool cores. Their relation is linear and the power generated by the Bondi accretion is large enough to compensate the radiative cooling of the cool cores. Although the `classical' Bondi accretion model is a greatly oversimplified one, the correlations we find here demonstrate that the accretion onto the SMBHs reflects broadly the properties of the Bondi accretion.

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arXiv2016

Evidence for a significant mixture of electron/positron pairs in FRII jets constrained by cocoon dynamics

We examine the plasma composition of relativistic jets in four FRII radio galaxies by analyzing the total cocoon pressure in terms of partial pressures of thermal and non-thermal electrons/positrons and protons. The total cocoon pressure is determined by cocoon dynamics via comparison of theoretical model with the observed cocoon shape. By inserting the observed number density of non-thermal electrons/positrons and the upper limit of thermal electron/positron number density into the equation of state, the number density of protons is constrained. We apply this method to four FRII radio galaxies (Cygnus A, 3C 219, 3C 223 and 3C 284), for which the total cocoon pressures have been already evaluated. We find that the positron-free plasma comprising of protons and electrons is ruled out, when we consider plausible particle distribution functions. In other words, the mixture of positrons is required for all four FRII radio galaxies; the number density ratio of electrons/positrons to protons is larger than two. Thus, we find that the plasma composition is independent of the jet power and the size of cocoons. We also investigate the additional contribution of thermal electrons/positrons and protons on the cocoon dynamics. When thermal electrons/positrons are absent, the cocoon is supported by the electron/ proton plasma pressure, while both electron/positron pressure supported and electron/proton plasma pressure supported cocoons are allowed if the number density of thermal electrons/positrons is about 10 times larger than that of non-thermal ones.

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arXiv2015

The young radio lobe of 3C 84: inferred gas properties in the central 10 parsec

We analyse the environment of the supermassive black hole (SMBH) in the centre of a massive elliptical galaxy NGC 1275 in the Perseus cluster, hosting the radio source 3C 84. We focus on the young radio lobe observed inside the estimated Bondi accretion radius. We discuss the momentum balance between the jet associated with the lobe and the surrounding gas. The results are compared with the proper motion of the radio lobe obtained with the very long baseline interferometry. We find that under assumption of a high-density environment >~ 100 cm^-3), the jet power must be comparable to the Eddington luminosity --- this is clearly inconsistent with the current moderate activity of 3C 84, which indicates instead that the jet is expanding in a very low density region (<~1 cm^-3), along the rotation axis of the accretion flow. The power required for the jet to expand in the low-density environment is comparable to the past average jet power estimated from the X-ray observations. We estimate the classical Bondi accretion rate, assuming that (1) gas accretion is spherically symmetric, (2) accretion is associated with the jet environment, and (3) the medium surrounding the jet is representative of the properties of the dominant accreting gas. We find that Bondi accretion is inconsistent with the estimated jet power. This means that either accretion of the cold gas in the NGC 1275 is more efficient than that of the hot gas, or the jets are powered by the SMBH spin.

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arXiv2015

The Fate of Dead Radio-loud Active Galactic Nuclei: A New Prediction of Long-lived Shell Emission

We examine the fate of a dead radio source in which jet injection from the central engine has stopped at an early stage of its evolution ($t = t_j \lesssim 10^5$ yr). To this aim, we theoretically evaluate the evolution of the emission from both the lobe and the shell, which are composed of shocked jet matter and a shocked ambient medium, respectively. Based on a simple dynamical model of expanding lobe and shell, we clarify how the broadband spectrum of each component evolves before and after the cessation of the jet activity. It is shown that the spectrum is strongly dominated by the lobe emission while the jet is active ($t \leq t_j$). On the other hand, once the jet activity has ceased ($t > t_j$), the lobe emission fades out rapidly, since fresh electrons are no longer supplied from the jet. Meanwhile, shell emission only shows a gradual decrease, since accelerated electrons are continuously supplied from the bow shock that is propagating into the ambient medium. As a result, overall emission from the shell overwhelms that from the lobe at wide range of frequencies from radio up to gamma-ray soon after the jet activity has ceased. Our result predicts a new class of dead radio sources that are dominated by shell emission. We suggest that the emission from the shell can be probed in particular at a radio wavelengths with the Square Kilometer Array (SKA) phase 1.

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arXiv2013

New class of Very High Energy gamma-ray emitter: radio-dark mini-shells surrounding AGN jets

We explore non-thermal emission from a shocked interstellar medium, which is identified as an expanding shell, driven by a relativistic jet in active galactic nuclei (AGNs). In this work, we particularly focus on parsec-scale size mini-shells surrounding mini radio lobes. From radio to X-ray band, the mini radio lobe emission dominates the faint emission from the mini-shell. On the other hand, we find that inverse-Compton (IC) emission from the shell can overwhelm the associated lobe emission at very high energy (VHE; E>100 GeV) gamma-ray range, because energy densities of synchrotron photons from the lobe and/or soft photons from the AGN nucleus are large and IC scattering effectively works. The predicted IC emission from nearby mini-shells can be detected with the Cherencov Telescope Array (CTA) and they are potentially a new class of VHE gamma-ray emitters.

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arXiv2012

Kiloparsec-scale Radio Structures in Narrow-line Seyfert 1 Galaxies

We report the finding of kiloparsec (kpc)-scale radio structures in three radio-loud narrow-line Seyfert 1 (NLS1) galaxies from the Faint Images of the Radio Sky at Twenty-centimeters (FIRST) of the Very Large Array (VLA), which increases the number of known radio-loud NLS1s with kpc-scale structures to six, including two gamma-ray emitting NLS1s (PMN J0948+0022 and 1H 0323+342) detected by the Fermi Gamma-ray Space Telescope. The detection rate of extended radio emissions in NLS1s is lower than that in broad-line active galactic nuclei (AGNs) with a statistical significance. We found both core-dominated (blazar-like) and lobe-dominated (radio-galaxy-like) radio structures in these six NLS1s, which can be understood in the framework of the unified scheme of radio-loud AGNs that considers radio galaxies as non-beamed parent populations of blazars. Five of the six NLS1s have (i) extended radio luminosities suggesting jet kinetic powers of >~10^44 erg/s, which is sufficient to make jets escape from hosts' dense environments, (ii) black holes of >~10^7 solar mass, which can generate the necessary jet powers from near-Eddington mass accretion, and (iii) two-sided radio structures at kpc scales, requiring expansion rates of ~0.01c--0.3c and kinematic ages of >~10^7 years. On the other hand, most typical NLS1s would be driven by black holes of <~10^7 solar mass in a limited lifetime of ~10^7 years. Hence the kpc-scale radio structures may originate in a small window of opportunity during the final stage of the NLS1 phase just before growing into broad-line AGNs.

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arXiv2012

Accretion Properties of High- and Low-Excitation Young Radio Galaxies

Young radio galaxies (YRGs) provide an ideal laboratory to explore the connection between accretion disk and radio jet thanks to their recent jet formation. We investigate the relationship between the emission-line properties, the black hole accretion rate, and the radio properties using a sample of 34 low-redshift (z < 0.4) YRGs. We classify YRGs as high-excitation galaxies (HEGs) and low-excitation galaxies (LEGs) based on the flux ratio of high-ionization to low-ionization emission lines. Using the Hα luminosities as a proxy of accretion rate, we find that HEGs in YRGs have \sim1 dex higher Eddington ratios than LEGs in YRGs, suggesting that HEGs have higher mass accretion rate or higher radiative efficiency than LEGs. In agreement with previous studies, we find that the luminosities of emission lines, in particular Hα, are correlated with radio core luminosity, suggesting that accretion and young radio activities are fundamentally connected.

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arXiv2012

Calorimetry of Active Galactic Nucleus jets: testing plasma composition in Cygnus A

We examine plasma composition of jets in active galactic nuclei through the comparison of the total pressure ($P$) with partial pressures of electrons and protons in a cocoon. The total pressure is estimated from the analysis of an expanding cocoon dynamics. We determine the average kinetic energy per particle for several representative cases of particle energy distribution such as one- and two-temperature thermal plasmas and non-thermal electrons by evaluating the dissipation of total kinetic energy of the jet into the internal energy of cocoon plasma. The number density of the total electrons/positrons ($n_{\pm}$) in the cocoon is constrained by using the particle supply from hot spots and the absence of thermal bremsstrahlung emission from radio lobes. By inserting $P$, $n_{\pm}$ and the particle energy of each population into the equation of state, the number density ($n_{p}$) and pressure ($P_{p}$) of protons in the cocoon can be constrained. Applying this method to Cygnus A, we find that (i) electron/positron ($e^{\pm}$) pairs always dominate in terms of number density, but that (ii) either an "$e^{\pm}$-supported cocoon (i.e., $P_{\pm} >P_{p}$)" or "proton-supported one (i.e, $P_{\pm} <P_{p}$)" is possible.

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arXiv2011

New Method for Exploring Super-Eddington AGNs by Near-infrared Observations

We propose a new method to explore the candidate super-Eddington active galactic nuclei (AGNs). We examine the properties of infrared (IR) emission from the inner edge of the dusty torus in AGNs, which are powered by super- or sub-Eddington accretion flows around black holes, by considering the dependence of the polar angle on the radiation flux of accretion flows (Watarai et al. 2005). We find that for super-Eddington AGNs, of which the mass accretion rate is more than 10^2 times larger than the Eddington rate, the ratio of the AGN IR luminosity and the disc bolometric luminosity is less than 10^-2, unless the half opening angle of the torus (theta_torus) is small (theta_torus <65 degree). This is due to the self-occultation effect, whereby the self-absorption at the outer region of the super-Eddington flow dilutes the illumination of the torus. Such a small luminosity ratio is not observed in sub-Eddington AGNs, whose mass accretion rate is comparable to or no more than 10 times larger than the Eddington mass accretion rate, except for extremely thin tori (theta_torus >85 degree). We also consider the properties of the near-IR (NIR) emission radiated from hot dust >1000 K. We find that super-Eddington AGNs have a ratio of the NIR luminosity to the bolometric luminosity, L_NIR,AGN/L_bol,disc, at least one order of magnitude smaller than for sub-Eddington AGNs for a wide range of half opening angle (theta_torus > 65 degree), for various types of dusty torus model. Thus, a relatively low L_NIR,AGN/L_bol,disc is a property that allows identification of candidate super-Eddington AGNs. Lastly, we discuss the possibility that NIR-faint quasars at redshift z=6 discovered by a recent deep SDSS survey may be young quasars whose black holes grow via super-Eddington accretion.

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arXiv2011

Infrared 3-4 Micron Spectroscopy of Nearby PG QSOs and AGN-Nuclear Starburst Connections in High-luminosity AGN Populations

We present the results of infrared L-band (3-4 micron) slit spectroscopy of 30 PG QSOs at z < 0.17, the representative sample of local high-luminosity, optically selected AGNs. The 3.3 micron polycyclic aromatic hydrocarbon (PAH) emission feature is used to probe nuclear (< a few kpc) starburst activity and to investigate the connections between AGNs and nuclear starbursts in PG QSOs. The 3.3 micron PAH emission is detected in the individual spectra of 5/30 of the observed PG QSOs. We construct a composite spectrum of PAH-undetected PG QSOs and discern the presence of the 3.3 micron PAH emission therein. We estimate the nuclear-starburst and AGN luminosities from the observed 3.3 micron PAH emission and 3.35 micron continuum luminosities, respectively, and find that the nuclear-starburst-to-AGN luminosity ratios in PG QSOs are similar to those of previously studied AGN populations with lower luminosities, suggesting that AGN-nuclear starburst connections are valid over the wide luminosity range of AGNs in the local universe. The observed nuclear-starburst-to-AGN luminosity ratios in PG QSOs with available supermassive black hole masses are comparable to a theoretical prediction based on the assumption that the growth of a supermassive black hole is controlled by starburst-induced turbulence.

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arXiv2009

Formation of High-redshift (z>6) Quasars Driven by Nuclear Starbursts

Based on the physical model of a supermassive black hole (SMBH) growth via gas accretion in a circumnuclear disk (CND) proposed by Kawakatu & Wada (2008), we describe the formation of high-$z$ ($z > 6$) quasars (QSOs) whose BH masses are M_{BH}> 10^{9} M_{\odot}. We derive the necessary conditions to form QSOs at z > 6 by only gas accretion: (i) A large mass supply with M_{sup} > 10^{10}M_{\odot} from host galaxies to CNDs, because the final BH mass is only 1-10% of the total supplied mass from QSO hosts. (ii) High star formation efficiency for a rapid BH growth. We also find that if the BH growth is limited by the Eddington accretion, the final BH mass is greatly suppressed. Thus, the super-Eddington growth is required for the QSO formation. The evolution of the QSO luminosity depends on the redshift z_{i} at which accretion onto a seed BH is initiated. In other words, the brighter QSOs at z >6 favor the late growth of SMBHs (i.e., z_{i}=10) rather than early growth (i.e., z_{i}=30). Moreover, we predict the observable properties and the evolution of QSOs at z >6. In a QSO phase, there should exist a stellar rich massive CND, whose gas mass is about 10% of the dynamical mass inside 0.1-1 kpc}. On the other hand, in a phase where the BH grows (i.e., a proto-QSO phase), the proto-QSO has a gas rich massive CNDs whose gas mass is comparable to the dynamical mass (abridged).

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