Yan-Mei Chen

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 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).

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.

Evidence for Rapidly Spinning Black Holes in Quasars

It has long been believed that accretion onto supermassive black holes powers quasars, but there are still relatively few observational constraints on the spins of the black holes. We address this problem by estimating the average radiative efficiencies of a large sample of quasars selected from the Sloan Digital Sky Survey, by combining their luminosity function and their black hole mass function. Over the redshift interval 0.4 < z < 2.1, we find that quasars have average radiative efficiencies of ~30%-35%, strongly suggesting that their black holes are rotating very rapidly, with specific angular momentum a ≈ 1, a value that remains roughly constant with redshift. The average radiative efficiency could be reduced by a factor of ~2, depending on the adopted zero point for the black hole mass scale. The inferred large spins and their lack of significant evolution are in agreement with the predictions of recent semianalytical models of hierarchical galaxy formation if black holes gain most of their mass through accretion.

Episodic random accretion and the cosmological evolution of supermassive black hole spins

The growth of supermassive black holes (BHs) located at the centers of their host galaxies comes mainly from accretion of gas, but how to fuel them remains an outstanding unsolved problem in quasar evolution. This issue can be elucidated by quantifying the radiative efficiency parameter (

Cosmological Evolution of the Duty Cycle of Quasars

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THE STARBURST-ACTIVE GALACTIC NUCLEUS CONNECTION: THE ROLE OF YOUNG STELLAR POPULATIONS IN FUELING SUPERMASSIVE BLACK HOLES

) as a function of redshift, which also provides constraints on the average spin of the BHs and its possible evolution with time. We derive a formalism to link

Feedback limits rapid growth of seed black holes at high redshift

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Suppressed star formation in circumnuclear regions in seyfert galaxies

with the luminosity density, BH mass density, and duty cycle of quasars, quantities we can estimate from existing quasar and galaxy survey data. We find that

The center of activity in the compact steep-spectrum superluminal source 3C 138

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