Wei-Hao Bian

A SYSTEMATIC ANALYSIS OF Fe II EMISSION IN QUASARS: EVIDENCE FOR INFLOW TO THE CENTRAL BLACK HOLE

Broad Fe II emission is a prominent feature of the optical and ultraviolet spectra of quasars. We report on a systematical investigation of optical Fe II emission in a large sample of 4037 z < 0.8 quasars selected from the Sloan Digital Sky Survey. We have developed and tested a detailed line-fitting technique, taking into account the complex continuum and narrow and broad emission-line spectra. Our primary goal is to quantify the velocity broadening and velocity shift of the Fe II spectrum in order to constrain the location of the Fe II-emitting region and its relation to the broad-line region. We find that the majority of quasars show Fe II emission that is redshifted, typically by similar to 400 km s(-1), but up to 2000 kms (-1), with respect to the systemic velocity of the narrow-line region or of the conventional broad-line region as traced by the H beta line. Moreover, the line width of Fe II is significantly narrower than that of the broad component of H beta. We show that the magnitude of the Fe II redshift correlates inversely with the Eddington ratio, and that there is a tendency for sources with redshifted Fe II emission to show red asymmetry in the H beta line. These characteristics strongly suggest that Fe II originates from a location different from, and most likely exterior to, the region that produces most of H beta. The Fe II-emitting zone traces a portion of the broad-line region of intermediate velocities whose dynamics may be dominated by infall.

Active Galactic Nuclei with Double-peaked Narrow Lines: Are They Dual AGNs?

Double-peaked [O III] profiles in active galactic nuclei (AGNs) may provide evidence for the existence of dual AGNs, but a good diagnostic for selecting them is currently lacking. Starting from similar to 7000 active galaxies in Sloan Digital Sky Survey DR7, we assemble a sample of 87 type 2 AGNs with double-peaked [O III] profiles. The nuclear obscuration in the type 2 AGNs allows us to determine redshifts of host galaxies through stellar absorption lines. We typically find that one peak is redshifted and another is blueshifted relative to the host galaxy. We find a strong correlation between the ratios of the shifts and the double peak fluxes. The correlation can be naturally explained by the Keplerian relation predicted by models of co-rotating dual AGNs. The current sample statistically favors that most of the [O III] double-peaked sources are dual AGNs and disfavors other explanations, such as rotating disk and outflows. These dual AGNs have a separation distance at similar to 1 kpc scale, showing an intermediate phase of merging systems. The appearance of dual AGNs is about similar to 10(-2), impacting on the current observational deficit of binary supermassive black holes with a probability of similar to 10(-4) (Boroson & Lauer).

ACTIVE GALACTIC NUCLEI WITH DOUBLE-PEAKED NARROW LINES: ARE THEY DUAL ACTIVE GALACTIC NUCLEI?

Double-peaked [O III] profiles in active galactic nuclei (AGNs) may provide evidence for the existence of dual AGNs, but a good diagnostic for selecting them is currently lacking. Starting from similar to 7000 active galaxies in Sloan Digital Sky Survey DR7, we assemble a sample of 87 type 2 AGNs with double-peaked [O III] profiles. The nuclear obscuration in the type 2 AGNs allows us to determine redshifts of host galaxies through stellar absorption lines. We typically find that one peak is redshifted and another is blueshifted relative to the host galaxy. We find a strong correlation between the ratios of the shifts and the double peak fluxes. The correlation can be naturally explained by the Keplerian relation predicted by models of co-rotating dual AGNs. The current sample statistically favors that most of the [O III] double-peaked sources are dual AGNs and disfavors other explanations, such as rotating disk and outflows. These dual AGNs have a separation distance at similar to 1 kpc scale, showing an intermediate phase of merging systems. The appearance of dual AGNs is about similar to 10(-2), impacting on the current observational deficit of binary supermassive black holes with a probability of similar to 10(-4) (Boroson & Lauer).

The Eddington ratios in Seyfert 2 galaxies with and without hidden broad-line regions

Using a large sample of 90 Seyfert 2 galaxies (Sy2s) with spectropolarimetric observations, we test the suggestion that the presence of hidden broad-line regions (HBLRs) in Sy2s depends upon the Eddington ratio. The stellar velocity dispersion and extinction-corrected [O III] luminosity are used to derive the masses of central supermassive black holes and the Eddington ratio. We find that (1) below an Eddington ratio threshold of 10(-1.37), all of the objects but one are non-HBLR Sy2s, while at higher Eddington ratios there is no obvious distinction in the Eddington ratio and black hole mass distributions between Sy2s with and without HBLRs; (2) almost no low-luminosity Sy2s (e.g., L vertical bar O III vertical bar 10(41) ergs s(-1)), the detectability of HBLRs is very high, similar to 85%. These results suggest that AGN luminosity plays a major role in the failure to detect HBLRs in low-luminosity Sy2s, while for high-luminosity Sy2s the detectability of HBLRs depends not only upon the AGN activity, but also upon the torus obscuration.

Hβ Profiles in Quasars: Evidence for an Intermediate-Line Region

We report on a systematic investigation of the H beta and Fe II emission lines in a sample of 568 quasars within z < 0.8 selected from the Sloan Digital Sky Survey. The conventional broad H beta emission line can be decomposed into two components-one with intermediate velocity width and another with very broad width. The velocity shift and equivalent width of the intermediate-width component do not correlate with those of the very broad component of H beta but its velocity shift and width do resemble Fe II. Moreover, the width of the very broad component is roughly 2.5 times that of the intermediate-width component. These characteristics strongly suggest the existence of an intermediate-line region, whose kinematics seem to be dominated by infall, located at the outer portion of the broad-line region.

On X-ray variability in narrow-line and broad-line active galactic nuclei

We assembled a sample of broad-line and narrow-line active galactic nuclei (AGNs) observed by ASCA, the excess variances of which have been determined. The central black hole masses in this sample can be obtained from the reverberation mapping method and the width of the Hβ emission line. Using the black hole masses and the bolometric luminosity, the Eddington ratio (the ratio of the ionizing luminosity to the Eddington luminosity) can also be obtained. We confirmed the strong anticorrelation between X-ray variability and the central black hole mass found by Lu & Yu. In addition, we found that narrow-line Seyfert 1 galaxies (NLS1s) also follow this relation, with a larger scatter, and that there is only a weak correlation between the X-ray variability and the Eddington ratio, which suggests that rapid variability and narrow lines in NLS1s are mainly due to small central black holes in NLS1s, not the difference of circumnuclear gas around NLS1s. A strong correlation was found between the hard X-ray photon index and the Eddington ratio. If the suggestion of two distinct accretion classes [namely advection-dominated accretion flow (ADAF) and thin disc accretion] in AGNs is correct, the strong correlation between the photon index and the Eddington ratio shows that there exists a kind of two-zone accretion disc, in which the outer zone is a thin disc and the inner zone is an ADAF disc. Otherwise, the accretion process is thin disc accretion and ADAF accretion is not required.

Black hole masses in narrow-line Seyfert 1 galaxies

The masses of central supermassive black holes in a soft X-ray-selected sample of the narrow-line Seyfert 1 galaxies (NLS I s) are estimated by various methods to test the theoretical models. Apart from the methods using the Hβ linewidth and the [O III] linewidth, soft X-ray excess as a prominent character of NLS 1 s is used to estimate the black hole masses. The virial mass derived from the Hβ linewidth assuming random orbits of broad-line regions (BLRs) is consistent with that from the soft X-ray bump luminosity for NLS 1s, but with a larger scatter. The virial black hole masses showed that most of NLS1s are in the super-Eddington accretion state, while most of broad-line Seyfert 1 galaxies are not. We found that the black hole mass estimated from the [O III] linewidth is not in agreement with above two methods. Using the Eddington limit relation for the super-Eddington accretion suggested by Wang, we found that there are 16 NLSIs satisfied by this Eddington limit relation. The masses of these 16 NLS1s derived from X-ray luminosity are systematically larger than that from Hβ linewidth assuming random BLRs orbits. If the mass derived from X-ray luminosity is true, the mean disc inclination to the line of sight in these 16 NLS s is approximately 17°, which provided new support for the pole-on orientation effect in NLS 1 s.

Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. IV. H

We have completed two years of photometric and spectroscopic monitoring of a large number of active galactic nuclei (AGNs) with very high accretion rates. In this paper, we report on the result of the second phase of the campaign, during 2013-2014, and the measurements of five new H beta time lags out of eight monitored AGNs. All five objects were identified as super-Eddington accreting massive black holes (SEAMBHs). The highest measured accretion rates for the objects in this campaign are (M) over dot(center dot) greater than or similar to 200, (M) over dot(center dot) = M over dot(center dot)/L(Edd)c(-2), (M) over dot(center dot) is the mass accretion rates, L-Edd is the Eddington luminosity and c is the speed of light. We find that the H beta time lags in SEAMBHs are significantly shorter than those measured in sub-Eddington AGNs, and the deviations increase with increasing accretion rates. Thus, the relationship between broad-line region size (R-H beta) and optical luminosity at 5100 angstrom, R-H beta-L-5100, requires accretion rate as an additional parameter. We propose that much of the effect may be due to the strong anisotropy of the emitted slim-disk radiation. Scaling R-H beta by the gravitational radius of the black hole (BH), we define a new radius-mass parameter (Y) and show that it saturates at a critical accretion rate of (M) over dot(c) = 6 similar to 30, indicating a transition from thin to slim accretion disk and a saturated luminosity of the slim disks. The parameter Y is a very useful probe for understanding the various types of accretion onto massive BHs. We briefly comment on implications to the general population of super-Eddington AGNs in the universe and applications to cosmology.

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Time Lags and Implications for Super-Eddington Accretion

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