458 research outputs found
Spectral properties of the narrow-line region in Seyfert galaxies selected from the SDSS-DR7
Although the properties of the narrow-line region (NLR) of active galactic
nuclei(AGN) have been deeply studied by many authors in the past three decades,
many questions are still open. The main goal of this work is to explore the NLR
of Seyfert galaxies by collecting a large statistical spectroscopic sample of
Seyfert 2 and Intermediate-type Seyfert galaxies having a high signal-to-noise
ratio in order to take advantage of a high number of emission-lines to be
accurately measured. 2153 Seyfert 2 and 521 Intermediate-type Seyfert spectra
were selected from Sloan Digital Sky Survey - Data Release 7 (SDSS-DR7) with a
diagnostic diagram based on the oxygen emission-line ratios. All the
emission-lines, broad components included, were measured by means of a
self-developed code, after the subtraction of the stellar component. Physical
parameters, such as internal reddening, ionization parameter, temperature,
density, gas and stellar velocity dispersion were determined for each object.
Furthermore, we estimated mass and radius of the NLR, kinetic energy of the
ionized gas, and black-hole accretion rate. From the emission-line analysis and
the estimated physical properties, it appears that the NLR is similar in
Seyfert 2 and Intermediate-Seyfert galaxies. The only differences, lower
extinction, gas kinematics in general not dominated by the host galaxy
gravitational potential and higher percentage of [O III]5007 blue asymmetries
in Intermediate-Seyfert can be ascribed to an effect of inclination of our line
of sight with respect to the torus axis.Comment: Accepted for publication in MNRA
A spectroscopic analysis of a sample of narrow-line Seyfert 1 galaxies selected from the Sloan Digital Sky Survey
We revisited the spectroscopic characteristics of narrow-line Seyfert 1
galaxies (NLS1s) by analysing a homogeneous sample of 296 NLS1s at redshift
between 0.028 and 0.345, extracted from the Sloan Digital Sky Survey (SDSS-DR7)
public archive. We confirm that NLS1s are mostly characterized by Balmer lines
with Lorentzian profiles, lower black hole masses and higher Eddington ratios
than classic broad-line Seyfert 1 (BLS1s), but they also appear to be active
galactic nuclei (AGNs) contiguous with BLS1s and sharing with them common
properties. Strong Fe II emission does not seem to be a distinctive property of
NLS1s, as low values of Fe II/H are equally observed in these AGNs. Our
data indicate that Fe II and Ca II kinematics are consistent with the one of
H. On the contrary, O I 8446 seems to be systematically
narrower and it is likely emitted by gas of the broad-line region more distant
from the ionizing source and showing different physical properties. Finally,
almost all NLS1s of our sample show radial motions of the narrow-line region
highly-ionised gas. The mechanism responsible for this effect is not yet clear,
but there are hints that very fast outflows require high continuum luminosities
(> erg/s) or high Eddington ratios (log(L/L)
> -0.1).Comment: 27 pages, 31 figures, 4 tables, accepted for publication in MNRA
[O III] line properties in two samples of radio-emitting narrow-line Seyfert 1 galaxies
The [O III] 4959,5007 lines are a useful proxy to test the
kinematic of the narrow-line region (NLR) in active galactic nuclei (AGN). In
AGN, and particularly in narrow-line Seyfert 1 galaxies (NLS1s) these lines
often show few peculiar features, such as blue wings, often interpreted as
outflowing component, and a shift typically toward lower wavelengths of
the whole spectroscopic feature in some exceptional sources, the so-called blue
outliers, which are often associated to strong winds. We investigated the
incidence of these peculiarities in two samples of radio-emitting NLS1s, one
radio-loud and one radio-quiet. We also studied a few correlations between the
observational properties of the [O III] lines and those of the AGN. Our aim was
to understand the difference between radio-quiet and radio-loud NLS1s, which
may in turn provide useful information on the jet formation mechanism. We find
that the NLR gas is much more perturbed in radio-loud than in radio-quiet
NLS1s. In particular the NLR dynamics in -ray emitting NLS1s appears to
be highly disturbed, and this might be a consequence of interaction with the
relativistic jet. The less frequently perturbed NLR in radio-quiet NLS1s
suggests instead that these sources likely do not harbor a fully developed
relativistic jet. Nonetheless blue-outliers in radio-quiet NLS1s are observed,
and we interpret them as a product of strong winds.Comment: 16 pages, 13 figures, 7 tables, accepted for publication on Astronomy
& Astrophysic
Are Boltzmann Plots of Hydrogen Balmer lines a tool for identifying a subclass of S1 AGN?
It is becoming clear that we can define two different types of nearby AGN
belonging to the Seyfert 1 class (S1), on the basis of the match of the
intensities of their Broad Balmer Lines (BBL) with the Boltzmann Plots (BP).
These two types of S1 galaxies, that we call BP-S1 and NoBP-S1, are
characterized, in first approximation, by Broad Line Regions (BLR) with
different structural and physical properties. In this communication, we show
that these features can be well pointed out by a multi-wavelength analysis of
the continuum and of the broad recombination Hydrogen lines, that we carry out
on a sample of objects detected at optical and X-ray frequencies. The
investigation is addressed to verify whether BP-S1 are the ideal candidates for
the study of the kinematical and structural properties of the BLR, in order to
derive reliable estimates of the mass of their central engine and to constrain
the properties of their nuclear continuum spectrum.Comment: 26 pages, 4 figures (1 multi-paged). Accepted for publication on
Advances in Space Research. Contribution to the IX SCSLS
Perfect preferential orientation of nitrogen-vacancy defects in a synthetic diamond sample
We show that the orientation of nitrogen-vacancy (NV) defects in diamond can
be efficiently controlled through chemical vapor deposition (CVD) growth on a
(111)-oriented diamond substrate. More precisely, we demonstrate that
spontaneously generated NV defects are oriented with a ~ 97 % probability along
the [111] axis, corresponding to the most appealing orientation among the four
possible crystallographic axes. Such a nearly perfect preferential orientation
is explained by analyzing the diamond growth mechanism on a (111)-oriented
substrate and could be extended to other types of defects. This work is a
significant step towards the design of optimized diamond samples for quantum
information and sensing applications.Comment: 6 pages, 4 figure
X-Ray Grating Observations of Recurrent Nova T Pyxidis During The 2011 Outburst
The recurrent nova T Pyx was observed with the X-ray gratings of Chandra and
XMM-Newton, 210 and 235 days, respectively, after the discovery of the 2011
April 14 outburst. The X-ray spectra show prominent emission lines of C, N, and
O, with broadening corresponding to a full width at half maximum of ~2000-3000
km/s, and line ratios consistent with high-density plasma in collisional
ionization equilibrium. On day 210 we also measured soft X-ray continuum
emission that appears to be consistent with a white dwarf (WD) atmosphere at a
temperature ~420,000 K, partially obscured by anisotropic, optically thick
ejecta. The X-ray continuum emission is modulated with the photometric and
spectroscopic period observed in quiescence. The continuum at day 235 indicated
a WD atmosphere at a consistent effective temperature of 25 days earlier, but
with a lower flux. The effective temperature indicates a mass of ~1 solar mass.
The conclusion of partial WD obscuration is supported by the complex geometry
of non-spherically-symmetric ejecta confirmed in recent optical spectra
obtained with the Southern African Large Telescope (SALT) in November and
December of 2012. These spectra exhibited prominent [O III] nebular lines with
velocity structures typical of bipolar ejecta.Comment: Accepted to ApJ 2013 October 23, 14 pages, 9 figures, 3 table
Exploring NLS1 through the physical properties of their hosts
In this work we aim at addressing the still open question about the nature of
Narrow-Line Seyfert 1 (NLS1) galaxies: are they really active nuclei with lower
mass Black-Holes (BHs) than Seyfert 1 (S1) and quasars? Our approach is based
on the recently discovered physical connections between nuclear supermassive
BHs and their hosting spheroids (spiral bulges or ellipticals). In particular
we compare BH masses of NLS1s and S1s analyzing the properties of their hosts
by means of spectroscopic and photometric data in the optical wavelength
domain. We find that NLS1s fill the low BH mass and bulge luminosity values of
the BH mass - bulge magnitude relation, a result strongly suggesting that NLS1s
are active nuclei where less massive BHs are hosted by less massive bulges. The
correlation is good with a relatively small scatter fitting simultaneously
NLS1s, S1s and quasars. On the other hand, NLS1s seem to share the same stellar
velocity dispersion range of S1s in the BH mass - stellar velocity dispersion
relation, indicating that NLS1s have a smaller BH/bulge mass ratio than S1s.
These two conflicting results support in any case the idea that NLS1s could be
young S1s. Finally we do not confirm the significantly non linear BH--bulge
relation claimed by some authors
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