76 research outputs found
Relativistic plasmas in AGN jets - From synchrotron radiation to -ray emission
Relativistic jets of plasma are a key ingredient of many types of Active
Galactic Nuclei (AGN). Today we know that AGNs are powered by the accretion of
inter stellar material into the gravitational field of a Super Massive Black
Hole and that this process can release as much power as a whole galaxy, like
the Milky Way, from a region that is comparable to the Solar System in size.
Depending on the properties of the central energy source, a large fraction of
this power can be involved in the acceleration of magnetized plasmas at
relativistic speeds, to form large scale jets. The presence of jets affects the
spectrum of AGNs through the emission of synchrotron radiation and Inverse
Compton scattering of low energy photons, thus leading to a prominent
non-thermal spectrum, some times extending from radio frequencies all the way
up to -ray energies. Here we review some characteristic processes of
radiation emission in AGN jets, which lead to the emission of photons in the
radio, optical, X-ray and -ray bands, and we present the results of a
spectroscopic campaign of optical counterparts. We discuss our observations and
their connection with -ray properties in a scenario that traces the
role of relativistic jets in different classes of AGNs, detected both in the
local as well as in the remote Universe.Comment: 11 pages, 5 figures (3 in color), proceedings of the XXVIII School on
Physics of Ionized Gases (SPIG), accepted for publication on the European
Journal of Physics
An orientation-based unification of young jetted AGN: the case of 3C 286
In recent years, the old paradigm according to which only high-mass black
holes can launch powerful relativistic jets in active galactic nuclei (AGN) has
begun to crumble. The discovery of -rays coming from narrow-line
Seyfert 1 galaxies (NLS1s), usually considered young and growing AGN harboring
a central black hole with mass typically lower than 10 M, indicated
that also these low-mass AGN can produce powerful relativistic jets. The search
for parent population of -ray emitting NLS1s revealed their connection
with compact steep-spectrum sources (CSS). In this proceeding we present a
review of the current knowledge of these sources, we present the new important
case of 3C 286, classified here for the fist time as NLS1, and we finally
provide a tentative orientation based unification of NLS1s and CSS sources.Comment: 12 pages, 3 figures. Proceeding of the conference "Quasars at all
cosmic epochs", held in Padova, April 2-7, 2017, published on Frontiers in
Astronomy and Space Science
Extended narrow-line region in Seyfert galaxies
We present our recent results about the extended narrow-line region (ENLR) of
two nearby Seyfert 2 galaxies (IC 5063 and NGC 7212) obtained by modelling the
observed line profiles and spectra with composite models
(photoionization+shocks) in the different regions surrounding the AGN. Then, we
compare the Seyfert 2 ENLRs with the very extended one recently discovered in
the narrow-line Seyfert 1 (NLS1) galaxy Mrk 783. We have found several
evidences of interaction between the ISM of the galaxies and their radio jets,
such as a) the contribution of shocks in ionizing the high velocity gas, b) the
complex kinematics showed by the profile of the emission lines, c) the high
fragmentation of matter, etc. The results suggest that the ENLR of IC 5063 have
a hollow bi-conical shape, with one edge aligned to the galaxy disk, which may
cause some kind of dependence on velocity of the ionization parameter.
Regarding the Mrk 783 properties, it is found that the extension of the optical
emission is almost twice the size of the radio one and it seems due to the AGN
activity, although there is contamination by star formation around 12 arcsec
from the nucleus. Diagnostic diagrams excluded the contribution of star
formation in IC 5063 and NGC 7212, while the shock contribution was used to
explain the spectra emitted by their high velocity gas.Comment: 9 pages, 2 figures, proceeding of the conference "Quasars at all
cosmic epochs", accepted for publication in Front. Astron. Space Sci. - Milky
Way and Galaxie
Optical counterparts of undetermined type -ray Active Galactic Nuclei with blazar-like Spectral Energy Distributions
During its first four years of scientific observations, the Fermi Large Area
Telescope (Fermi-LAT) detected 3033 -ray sources above a 4
significance level. Although most of the extra-Galactic sources are active
galactic nuclei (AGN) of the blazar class, other families of AGNs are observed
too, while a still high fraction of detections () remains with
uncertain association or classification. According to the currently accepted
interpretation, the AGN -ray emission arises from inverse Compton (IC)
scattering of low energy photons by relativistic particles confined in a jet
that, in the case of blazars, is oriented very close to our line of sight.
Taking advantage of data from radio and X-ray wavelengths, which we expect to
be produced together with -rays, providing a much better source
localization potential, we focused our attention on a sample of -ray
Blazar Candidates of Undetermined Type (BCUs), starting a campaign of optical
spectroscopic observations. The main aims of our investigation include a census
of the AGN families that contribute to -ray emission and a study of
their redshift distribution, with the subsequent implications on the intrinsic
source power. We furthermore analyze which -ray properties can better
constrain the nature of the source, thus helping in the study of objects not
yet associated with a reliable low frequency counterpart. In this communication
we report on the instruments and techniques used to identify the optical
counterparts of -ray sources, we give an overview on the status of our
work, and we discuss the implications of a large scale study of -ray
emitting AGNs.Comment: 9 pages, 2 figures, proceedings of the 10th Serbian Conference on
Spectral Line Shapes in Astrophysics. JOAA, accepte
Models of emission line profiles and spectral energy distributions to characterize the multi-frequency properties of active galactic nuclei
The spectra of Active Galactic Nuclei (AGNs) are often characterized by a
wealth of emission lines with different profiles and intensity ratios that led
to a complicated classification. Their electro-magnetic radiation spans more
than 10 orders of magnitude in frequency. In spite of the differences between
various classes, the origin of their activity is attributed to a combination of
emitting components, surrounding an accreting Super Massive Black Hole, in the
so called Unified Model. Currently, the execution of sky surveys, with
instruments operating at various frequencies, provides the possibility to
detect and to investigate the properties of AGNs on very large statistical
samples. Thanks to the spectroscopic surveys that allow investigation of many
objects, we have the opportunity to place new constraints on the nature and
evolution of AGNs. In this contribution we present the results obtained by
working on multi-frequency data and we discuss their relations with the
available optical spectra. We compare our findings with the AGN Unified Model
predictions, and we present a revised technique to select AGNs of different
types from other line emitting objects. We discuss the multi-frequency
properties in terms of the innermost structures of the sources.Comment: 11 pages, 4 figures. Proceedings of the XI Serbian Conference on
Spectral Line Shapes in Astrophysics. Accepted for publication on Atom
Parent population of flat-spectrum radio-loud narrow-line Seyfert 1 galaxies
Flat-spectrum radio-loud Narrow-Line Seyfert 1 galaxies (NLS1s) are a
recently discovered class of -ray emitting Active Galactic Nuclei
(AGN), that exhibit some blazar-like properties which are explained with the
presence of a relativistic jet viewed at small angles. When blazars are
observed at larger angles they appear as radio-galaxies, and we expect to
observe an analogue parent population for beamed NLS1s. However, the number of
known NLS1s with the jet viewed at large angles is not enough. Therefore, we
tried to understand the origin of this deficit. Current hypotheses about the
nature of parent sources are steep-spectrum radio-loud NLS1s, radio-quiet NLS1s
and disk-hosted radio-galaxies. To test these hypotheses we built three samples
of candidate sources plus a control sample, and calculated their black hole
mass and Eddington ratio using their optical spectra. We then performed a
Kolmogorov-Smirnov statistical test to investigate the compatibility of our
different samples with a beamed population. Our results indicate that, when the
inclination angle increases, a beamed source appears as a steep-spectrum
radio-loud NLS1, or possibly even as a disk-hosted radio-galaxy with low black
hole mass and high Eddington ratio. Further investigations, involving larger
complete samples and observations at radio frequency, are needed to understand
the incidence of disk-hosted radio-galaxies in the parent population, and to
assess whether radio-quiet NLS1s can play a role, as well.Comment: 12 pages, 6 figures, accepted for publication by Astronomy and
Astrophysic
A new approach to produce calcium-phosphate coatings on titanium
In the study, hydroxyapatite-gelatin composite powders were synthesized from simulated body fluid (SBF) with gelatin content ranging from 1 to 3 wt. %. It was established that all the samples were single-phase and represented hydroxyapatite. The surface and morphological characteristics of the produced hydroxyapatite-gelatin (HAG) based coatings were studied. Uniform deposition of the composite on the titanium substrate surface (VT1-0) was found to occur on etched titanium samples. It is shown that exposure of titanium substrates with hydroxyapatite-gelatin (HAG) based coating to powerful ion beam can stimulate further growth of crystals and regeneration of the surface
Compact steep-spectrum sources as the parent population of flat-spectrum radio-loud NLS1s
Narrow-line Seyfert 1 galaxies (NLS1s) are an interesting subclass of active
galactic nuclei (AGN), which tipically does not exhibit any strong radio
emission. Seven percent of them, though, are radio-loud and often show a flat
radio-spectrum (F-NLS1s). This, along to the detection of -ray emission
coming from them, is usually interpreted as a sign of a relativistic beamed jet
oriented along the line of sight. An important aspect of these AGN that must be
understood is the nature of their parent population, in other words how do they
appear when observed under different angles. In the recent literature it has
been proposed that a specific class of radio-galaxies, compact-steep sources
(CSS) classified as high excitation radio galaxies (HERG), can represent the
parent population of F-NLS1s. To test this hypothesis in a quantitative way,in
this paper we analyzed the only two statistically complete samples of CSS/HERGs
and F-NLS1s available in the literature. We derived the black hole mass and
Eddington ratio distributions, and we built for the first time the radio
luminosity function of F-NLS1s. Finally, we applied a relativistic beaming
model to the luminosity function of CSS/HERGs, and compared the result with the
observed function of F-NLS1s. We found that compact steep-spectrum sources are
valid parent candidates and that F-NLS1s, when observed with a different
inclination, might actually appear as CSS/HERGs.Comment: 9 pages, 5 figures, 4 tables. Accepted for publication in Astronomy &
Astrophysic
Optical properties of two complementary samples of intermediate Seyfert galaxies
We present preliminary results of the analysis of optical spectra of two
complementary samples of Seyfert galaxies. The first sample was extracted from
a selection of the 4th Fermi Gamma-ray Large Area Telescope (4FGL) catalog, and
consists of 9 -ray emitting jetted Seyfert galaxies. The second one was
extracted from the Swift-BAT AGN Spectroscopic Survey (BASS), and is composed
of 38 hard-X ray selected Active Galactic Nuclei (AGN). These two samples are
complementary, with the former expected to have smaller viewing angles, while
the latter may include objects with larger viewing angles. We measured emission
line ratios to investigate whether the behavior of these Seyferts can be
explained in terms of obscuration, as suggested by the well-known Unified Model
(UM) of AGN, or if there are intrinsic differences due to the presence of jets,
outflows, or the evolution. We found no indications of intrinsic differences.
The UM remains the most plausible interpretation for these classes of objects
even if some results can be challenging for this model.Comment: 24 pages, 10 figures, conference proceeding "14th Serbian Conference
on Spectral Line Shapes in Astrophysics
- …