73 research outputs found
The sizes of BLRs and BH masses of double-peaked broad low-ionization emission line objects
In this paper, the sizes of the BLRs and BH masses of DouBle-Peaked broad
low-ionization emission line emitters (dbp emitters) are compared using
different methods: virial BH masses vs BH masses from stellar velocity
dispersions, the size of BLRs from the continuum luminosity vs the size of BLRs
from the accretion disk model. First, the virial BH masses of dbp emitters
estimated by the continumm luminosity and line width of broad H are
about six times (a much larger value, if including another dbp emitters, of
which the stellar velocity dispersions are traced by the line widths of narrow
emission lines) larger than the BH masses estimated from the relation which is a more accurate relation to estimate BH masses. Second, the
sizes of the BLRs of dbp emitters estimated by the empirical relation of
are about three times (a much larger value, if
including another dbp emitters, of which the stellar velocity dispersions are
traced by the line widths of narrow emission lines) larger than the mean
flux-weighted sizes of BLRs of dbp emitters estimated by the accretion disk
model. The higher electron density of BLRs of dbp emitters would be the main
reason which leads to smaller size of BLRs than the predicted value from the
continuum luminosity.Comment: 7 pages, two figures and one table. Accepted by MNRA
The Correlation Between Spectral Index And Accretion Rate For AGN
In this paper, we present a correlation between the spectral index
distribution (SED) and the dimensionless accretion rate defined as
for AGN. This quantity is used as a substitute of
the physical accretion rate. We select 193 AGN with both broad H and
broad H, and with absorption lines near MgI from SDSS
DR4. We determine the spectral index and dimensionless accretion rate after
correcting for both host galaxy contribution and internal reddening effects. A
correlation is found between the optical spectral index and the dimensionless
accretion rate for AGN, including low luminosity AGN ( sometimes called "dwarf AGN" (Ho et al. 1997)). The existence
of this correlation provides an independent method to estimate the central BH
masses for all types of AGN. We also find that there is a different correlation
between the spectral index and the BH masses for normal AGN and low luminosity
AGN, which is perhaps due to the different accretion modes in these two types
of nuclei. This in turn may lead to the different correlations between BH
masses and optical continuum luminosity reported previously (Zhang et al.
2007a), which invalidates the application of the empirical relationship found
by Kaspi et al. (2000, 2005) to low luminosity AGN in order to determine their
BLR sizes.Comment: 10 pages, 7 figures, accepted for publication in MNRA
GTC Spectra of z ~ 2.3 Quasars: Comparison with Local Luminosity Analogues
[Abridged] Context: The advent of 8-10m class telescopes makes possible for
the first time detailed comparison of quasars with similar luminosity and very
different redshifts. Aims: A search for z-dependent gradients in line emission
diagnostics and derived physical properties by comparing, in a narrow
bolometric luminosity range (log L ~ 46.1 +/- 0.4 [\ergss]), some of the most
luminous local (z < 0.6) quasars with some of the lowest luminosity sources yet
found at redshift z = 2.1 ~ 2.5. Method: Spectra for 22 high z sources were
obtained with the 10.4m Gran Telescopio Canarias (GTC) while the HST (largely
FOS) archive provides a low redshift control sample. Comparison is made in the
context of the 4D Eigenvector 1 formalism meaning that we divide both source
samples into high accreting Population A and low accreting Population B
sources. Results: CIV 1549 shows very similar properties at both redshifts
confirming at high redshift the CIV profile differences between Pop. A and B
that are well established in local quasars. The CIV blueshift that appears
quasi- ubiquitous in higher L sources is found in only half (Pop. A) of quasars
observed in both of our samples. A CIV evolutionary Baldwin effect is certainly
disfavored. We find evidence for lower metallicity in the GTC sample that may
point toward a gradient with z. No evidence for a gradient in black hole mass
or Eddington ratio is found. Conclusions: Spectroscopic differences established
at low redshift are also present in much higher redshift quasars. Given that
our samples involve sources with very similar luminosity the evidence for a
systematic metallicity decrease, if real, points toward an evolutionary effect.
Our samples appear representative of a slow evolving quasar population likely
present at all redshifts.Comment: To appear in Astronomy & Astrophysic
The size of BLRs of low luminous Active Galactic Nuclei
We study the size of BLRs of low luminosity Active Galactic Nuclei, also
called 'dwarf AGN', defined as having ()). We more than double the sample size analyzed previously (Wang &
Zhang 2003, hereafter Paper I). In this study we first confirm our previous
result that the sizes of BLRs of low luminosity AGN are larger than the ones
expected from the empirical relation valid for
'normal' AGN: Seyfert 1s and quasars, except for the objects with accretion
rate . Second, we find a positive correlation
between the line width of the narrow emission line (as tracer of velocity
dipersion and thus bulge and black hole mass) and the size of BLRs for both
normal and low luminosity AGN. In this paper we find a non-linear dependence of
the BLRs sizes of low luminosity AGN on BH masses. We also show that their
sizes of BLRs are more strongly dominated by the 'specific accretion rate'
defined as , than
by the masses of their cetral black holes. As an expected result, the distance
of emission regions of low-ionization broad H of NGC 4395 should be
consistent with the value from the empirical relation of , according to the high accretion rate.Comment: Accepted by MNRA
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