512 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
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
High resolution spectroscopy of the extended narrow-line region of IC 5063 and NGC 7212
We studied the properties of the gas of the extended narrow line region
(ENLR) of two Seyfert 2 galaxies: IC 5063 and NGC 7212. We analysed high
resolution spectra to investigate how the main properties of this region depend
on the gas velocity. We divided the emission lines in velocity bins and we
calculated several line ratios. Diagnostic diagrams and SUMA composite models
(photo-ionization + shocks), show that in both galaxies there might be evidence
of shocks significantly contributing in the gas ionization at high |V|, even
though photo-ionization from the active nucleus remains the main ionization
mechanism. In IC 5063 the ionization parameter depends on V and its trend might
be explained assuming an hollow bi-conical shape for the ENLR, with one of the
edges aligned with the galaxy disk. On the other hand, NGC 7212 does not show
any kind of dependence. The models show that solar O/H relative abundances
reproduce the observed spectra in all the analysed regions. They also revealed
an high fragmentation of the gas clouds, suggesting that the complex kinematics
observed in these two objects might be caused by interaction between the ISM
and high velocity components, such as jets.Comment: 29 pages, 32 figures, accepted for publication in MNRA
Nuclear activity and star formation properties of Seyfert 2 galaxies
In order to characterize the amount of recent or ongoing stellar formation in
the circumnuclear region of active galaxies on a statistically sound basis, we
have studied the stellar component of the nuclear spectra in three different
samples of galaxies, namely Seyfert 2 galaxies (hereafter S2G), star-forming
galaxies (SFG) and passive normal galaxies (NG), i.e., no emission lines
observed, using Sloan Digital Sky Survey data (SDSS) (Adelman-McCarthy, 2008).
The stellar component of the observed spectra has been extracted using
STARLIGHT (Cid Fernandes et al., 2004), which fits an observed spectrum with a
model (template) spectrum obtained by combining a library of pre-defined simple
stellar populations spectra, with distinct ages and metallicities. The
resulting template spectra for the different samples of galaxies have been
compared to determine the features of the stellar emission component and to
evaluate the presence and intensity of the star formation in the nuclear
regions of different families of galaxies. From a first qualitative analysis it
results that the shape of the Spectral Energy Distribution (SED) of S2G and NG
is very similar, while that of SFG is characterized by a strong blue excess.
The presence of the 4000 A break in the spectra of S2G and NG together with the
lack of a strong blue continuum clearly indicate the absence of ongoing star
formation in the circumnuclear regions of S2G and obviously of NG. Anyway
traces of a recent star formation history are evident in the spectra of S2G
galaxies, which show a 4000 A break systematically shallower than in NG.Comment: Proceeding of the VII Serbian Conference on Spectral Line Shapes in
Astrophysic
CARTE: An Observation Station to Regulate Activity in a Learning Context
This chapter discusses the introduction of a new concept called "regulation" into a use model, which is part of a theoretical observation model called trace-based system (TBS). This concept defines a retroaction mechanism in an observation station. We present the results of experiments, in a learning context, with a prototype observation station called Collection, activity Analysis and Regulation based on Traces Enriched (CARTE)
Stellar velocity dispersion in NLS1 galaxies
Several authors recently explored the Black-Hole mass (M_BH) vs. stellar
velocity dispersion (sigma_*) relationship for Narrow Line Seyfert 1 galaxies
(NLS1s). Their results are more or less in agreement and seem to indicate that
NLS1s fill the region below the fit obtained by Tremaine et al. (2002), showing
a range of sigma_* similar to that of Seyfert 1 galaxies, and a lower M_BH.
Until now the [O III] width has been used in place of the stellar velocity
dispersion, but some indications begin to arise against the effectiveness of
the gaseous kinematics in representing the bulge potential at least in NLS1s.
Bian & Zhao (2004) stressed the urgency to produce true sigma_* measurements.
Here we present new stellar velocity dispersions obtained through direct
measurements of the Ca II absorption triplet (~ 8550 A) in the nuclei of 8 NLS1
galaxies. The resulting sigma_* values and a comparison with sigma_[O III]
confirm our suspects (see Botte et al. 2004) that [O III] typically
overestimates the stellar velocity dispersion and demonstrate that NLS1s follow
the M_BH-sigma_* relation as Seyfert 1, quasars and non-active galaxies.Comment: 5 pages, 4 figures, accepted for publication in MNRA
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