57 research outputs found
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
The CaFe Project: Optical FeII and Near-Infrared Ca II triplet emission in active galaxies. II. The driver(s) of the Ca II and Fe II and its potential use as a chemical clock
In this second paper in the series, we carefully analyze the observational
properties of the optical FeII and NIR CaII triplet properties as well as the
luminosity, black hole mass, and Eddington ratio in order to define the driving
mechanism behind the properties of our sample. Most of the significant
correlations are associated with CaII triplet. The CaII shows an inverse
Baldwin effect, bringing out the particular behavior of this ion with respect
to the other low-ionization lines such as H. We also performed a
Principal Component Analysis, where of the variance can be explained
by the first three principal components drawn from the FWHMs, luminosity, and
equivalent widths. The first principal component is primarily driven by the
combination of black hole mass and luminosity with a significance over
, which in turn is reflected in the strong correlation of the first
eigenvector with the Eddington ratio. Since the observational correlations are
better represented by the Eddington ratio, this could be the primary mechanism
behind the relations observed in our CaII-FeII sample. Since the calcium belong
to the -elements, the FeII/CaII flux ratio can be used as a chemical
clock for determining the metal content in AGN and trace the evolution of the
host galaxies. We confirm the negative enhancement of the ratio FeII/CaII by
the Eddington ratio, suggesting a metal enrichment of the BLR in
intermediate- with respect to low- objects. A larger sample, particularly
at , is needed to confirm the present results.Comment: 26 pages, 11 figures, 2 tables. Submitted to ApJ. Comments are
welcom
A 3-Dimensional study of the Local Environment of Bright IRAS Galaxies: The AGN/Starburst connection
We present a 3-dimensional study of the local ( kpc) and the
large scale ( 1 Mpc) environment of Bright IRAS Galaxies
(BIRGs). For this purpose we use 87 BIRGs located at high galactic latitudes
(with 0.0080.018) as well as a control sample of non-active
galaxies having the same morphological, redshift and diameter size
distributions as the corresponding BIRG sample. Using the Center for
Astrophysics (CfA2) and Southern Sky Redshift Survey (SSRS) galaxy catalogues
()as well as our own spectroscopic observations
() for a subsample of the original BIRG sample, we find that
the fraction of BIRGs with a close neighbor is significantly higher than that
of their control sample. Comparing with a related analysis of Sy1 and Sy2
galaxies of Koulouridis et al. (2006) we find that BIRGs have a similar
environment as Sy2s, although the fraction of BIRGs with a bright close
neighbor is even higher than that of Sy2 galaxies. An additional analysis of
the relation between FIR colors and the type of activity of each BIRG shows a
significant difference between the colors of strongly-interacting and
non-interacting starbursts and a resemblance between the colors of
non-interacting starbursts and Sy2s. Our results support the view where close
interactions can drive molecular clouds towards the galactic center, triggering
starburst activity and obscuring the nuclear activity. When the close neighbor
moves away, starburst activity is reduced with the simultaneous appearance of
an obscured (type 2) AGN. Finally, the complete disentanglement of the pair
gives birth to an unobscured (type 1) AGN.Comment: Accepted for publication in The Astrophysical Journal,10 pages, 4
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