58 research outputs found
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
The physics of the extended narrow-line region in active galactic nuclei
The extended narrow-line region (ENLR) is one of the most interesting and less studied structures typical of active galactic nuclei (AGN). It is made of gas, ionized by the radiation produced in the inner region of the AGN. Its spectral properties are similar to those of the narrow-line region (NLR), but the extension of ENLR is usually larger than 1 kpc (there are objects with ENLR larger than 20 kpc) while the NLR is often concentrated in a radius of some hundreds parsecs from the AGN. In this work I used optical spectra and radio and optical images to investigate the properties of some of these peculiar structures. In particular, I firstly used high resolution spectra and models combining photo-ionization and shocks to study the physical conditions of the gas in the ENLR of two nearby sources, NGC 7212 and IC
5063. The spectral resolution of the data allowed to resolve all the observed lines, which show a complex profile characterized by multiple peaks, asymmetries and bumps. Moreover, it allowed me to investigate the behavior of the gas properties as a function of its velocity. In this way I discovered that, in both AGN, shocks might give an important contribution to the ionization of the gas moving at high velocities. This property, together with the complex kinematics of the gas, might be the result of the interaction between the AGN jets and the interstellar medium (ISM) of the galaxies.
Then, I started investigating the relation between extended optical emission and extended radio emission. For this reason, I looked for new extended radio structures in a VLA survey at 5 GHz of a sample of AGN belonging to the peculiar class of narrow-line Seyfert 1 galaxies (NLS1s). The first and most interesting result of this survey was the discovery of a very interesting radio emission, probably a relic, in Mrk 783, a nearby NLS1. An optical follow-up of the source revealed the presence of an ENLR. The structure is one of the largest discovered so far, with a maximum extension of 38 kpc just aligned with the most extended part of the radio emission. The host galaxy also shows signs of a recent merging with a companion, and it might be in the first stages of interaction with another nearby source
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
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
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
Jetted narrow-line Seyfert 1 galaxies breaking the jet paradigm -- a comprehensive study of host galaxy morphologies
Narrow-line Seyfert 1 (NLS1) galaxies are unevolved active galactic nuclei
(AGN) that exist predominantly in spiral galaxies. However, mostly due to the
small number of sources studied, it has been under debate whether also the
hosts of jetted NLS1 galaxies, a particular subclass of these sources hosting a
relativistic jet, are disk-like, or elliptical, as the hosts of more powerful
jetted AGN. We studied the host morphologies of 14 NLS1 galaxies, 11 of which
have been detected at 37 GHz indicating that these sources harbour relativistic
jets. The J- and Ks-band data used in this study were obtained with the Nordic
Optical Telescope (NOT). We performed the photometric decomposition of the host
galaxy using the band that gave a better fit, and additionally, created colour
maps of all sources that had both a J- and a Ks-band observation. We were able
to successfully model 12 sources, nine of which most likely have disk-like
morphology. Of the remaining sources, one source could possibly be hosted
either in a disk-like or a dwarf galaxy, and in two cases the results are
inconclusive. Only one of our sources shows clear signs of interaction, but the
colour maps of most of our sources hint at ample dust in the nuclei, possibly
indicating earlier minor mergers, that can go unnoticed due to the limited
resolution of these observations. Our results further support disk-like
galaxies as the predominant host type of jetted NLS1 galaxies. Most
importantly, with the number of modelled hosts of jetted NLS1s now exceeding
50, with only a few elliptical hosts, it seems to be safe to conclude that also
disk-like galaxies are able to launch and maintain relativistic jets, and that
the traditional jet paradigm stating that only massive elliptical galaxies are
capable of hosting relativistic jets is severely outdated.Comment: 24 pages, 40 figures, 17 tables, accepted to A&
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
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