142 research outputs found
Hard - X-rays selected Active Galactic Nuclei. I. A radio view at high-frequencies
A thorough study of radio emission in Active Galactic Nuclei (AGN) is of
fundamental importance to understand the physical mechanisms responsible for
the emission and the interplay between accretion and ejection processes. High
frequency radio observations can target the nuclear contribution of smaller
emitting regions and are less affected by absorption. We present JVLA 22 and 45
GHz observations of 16 nearby (0.003z0.3) hard - X-rays selected AGN
at the (sub)-kpc scale with tens uJy beam sensitivity. We detected 15/16
sources, with flux densities ranging from hundreds uJy beam to tens Jy
(specific luminosities from 10 to 10 at
22 GHz). All detected sources host a compact core, with 8 being core-dominated
at either frequencies, the others exhibiting also extended structures. Spectral
indices range from steep to flat/inverted. We interpret this evidence as either
due to a core+jet system (6/15), a core accompanied by surrounding star
formation (1/15), to a jet oriented close to the line of sight (3/15), to
emission from a corona or the base of a jet (1/15), although there might be
degeneracies between different processes. Four sources require more data to
shed light on their nature. We conclude that, at these frequencies, extended,
optically-thin components are present together with the flat-spectrum core. The
relation is roughly followed, indicating a possible
contribution to radio emission from a hot corona. A weakly significant
correlation between radio core (22 and 45 GHz) and X-rays luminosities is
discussed in the light of an accretion-ejection framework.Comment: Accepted for publication on MNRA
IC 485:a new candidate disk-maser galaxy at 100 Mpc distance. Milliarcsecond resolution study of the galaxy nucleus and of the megamaser
Masers are a unique tool to investigate the emitting gas in the innermost
regions of AGNs and to map accretion disks and tori orbiting around
supermassive black holes. IC485, which is classified as a LINER or Seyfert
galaxy, hosts a bright water maser whose nature is still under debate. Indeed,
this might be either a nuclear disk maser, a jet/outflow maser, or even the
very first `inclined water maser disk'. We aim to investigate the nature of the
maser by determining the location and the distribution of the maser emission at
mas resolution and by associating it with the main nuclear components of IC485.
In a broader context, this work might also provide further information for
better understanding the physics and the disk/jet geometry in LINER or Seyfert
galaxies. We observed in 2018 the nuclear region of IC485 in continuum and
spectral-line mode with the VLBA and the EVN at L, C, and K bands (linear
scales from ~3 to 0.2 pc). We detected 2 water maser components separated in
velocity by 472 km/s, with one centred at the systemic velocity of the nuclear
region and the other at a red-shifted velocity. We measured for the first time
the absolute positions of these components with an accuracy of ~0.1 mas.
Assuming a maser associated with an edge-on disk in Keplerian rotation, the
estimated enclosed mass is M_BH = 1.2 x 10^7 M_sun, consistent with the
expected mass for a SMBH in a LINER or Seyfert galaxy. The linear distribution
of the maser components and a comparison with the high sensitivity GBT spectrum
strongly suggest that the bulk of the maser emission is associated with an
edge-on accretion disk. This makes IC485 a new candidate for a disk-maser
galaxy at the distance of 122 Mpc. In particular, thanks to the upcoming radio
facilities (e.g., the SKA and the ngVLA) IC485 will play an important role in
our understanding of AGNs in an unexplored volume of Universe.Comment: 13 pages, 10 figures, 6 tables, accepted by Astronomy & Astrophysic
The evolution of HCO in molecular clouds using a novel chemical post-processing algorithm
Modeling the internal chemistry of molecular clouds is critical to accurately
simulating their evolution. To reduce computational expense, 3D simulations
generally restrict their chemical modeling to species with strong heating and
cooling effects. We address this by post-processing tracer particles in the
SILCC-Zoom molecular cloud simulations. Using a chemical network of 39 species
and 299 reactions (including freeze-out of CO and HO), and a novel
iterative algorithm to reconstruct a filled density grid from sparse tracer
particle data, we produce time-dependent density distributions for various
species. We focus upon the evolution of HCO, which is a critical formation
reactant of CO but is not typically modeled on-the-fly. We analyse the
evolution of the tracer particles to assess the regime in which HCO
production preferentially takes place. We find that the HCO content of the
cold molecular gas forms in situ around n_\textrm{HCO^+}\simeq10^3-
cm, over a time-scale of approximately 1 Myr, rather than being
distributed to this density regime via turbulent mixing from deeper in the
cloud. We further show that the dominant HCO formation pathway is dependent
on the visual extinction, with the reaction H + CO contributing 90% of
the total HCO production flux above . Using our novel
grid reconstruction algorithm, we produce the very first maps of the HCO
column density, (HCO), and show that it reaches values as high as
cm. We find that 50% of the HCO mass is located in an
-range of 10-30, and in a density range of
- cm. Finally, we compare our (HCO) maps to
recent observations of W49A and find good agreement.Comment: 23 pages including appendix, 20 figures, submitted to MNRAS, comments
are welcom
Accretion and nuclear activity in Virgo early-type galaxies
We use Chandra observations to estimate the accretion rate of hot gas onto
the central supermassive black hole in four giant (of stellar mass 10E11 -
10E12 solar masses) early-type galaxies located in the Virgo cluster. They are
characterized by an extremely low radio luminosity, in the range L < 3E25 -
10E27 erg/s/Hz. We find that, accordingly, accretion in these objects occurs at
an extremely low rate, 0.2 - 3.7 10E-3 solar masses per year, and that they
smoothly extend the relation accretion - jet power found for more powerful
radio-galaxies. This confirms the dominant role of hot gas and of the galactic
coronae in powering radio-loud active galactic nuclei across ~ 4 orders of
magnitude in luminosity. A suggestive trend between jet power and location
within the cluster also emerges.Comment: Accepted for publication in A&
Searching for Compton-thick active galactic nuclei at z~0.1
Using a suite of X-ray, mid-IR and optical active galactic nuclei (AGN)
luminosity indicators, we search for Compton-thick (CT) AGNs with intrinsic
L_X>10^42erg/s at z~0.03-0.2, a region of parameter space which is currently
poorly constrained by deep narrow-field and high-energy (E>10keV) all-sky X-ray
surveys. We have used the widest XMM-Newton survey (the serendipitous source
catalogue) to select a representative sub-sample (14; ~10%) of the 147 X-ray
undetected candidate CT AGNs in the Sloan Digital Sky Survey (SDSS) with
f_X/f_[OIII]<1; the 147 sources account for ~50% of the overall Type-2 AGN
population in the SDSS-XMM overlap region. We use mid-IR spectral decomposition
analyses and emission-line diagnostics, determined from pointed Spitzer-IRS
spectroscopic observations of these candidate CT AGNs, to estimate the
intrinsic AGN emission (predicted L_X,2-10keV (0.2-30)x10^42erg/s). On the
basis of the optical [OIII], mid-IR [OIV] and 6um AGN continuum luminosities we
conservatively find that the X-ray emission in at least 6/14 (>43%) of our
sample appear to be obscured by CT material with N_H>1.5x10^24cm^-2. Under the
reasonable assumption that our 14 AGNs are representative of the overall X-ray
undetected AGN population in the SDSS-XMM parent sample, we find that >20% of
the optical Type-2 AGN population are likely to be obscured by CT material.
This implies a space-density of log(Phi) >-4.9Mpc^-3 for CT AGNs with
L_X>10^42erg/s at z~0.1, which we suggest may be consistent with that predicted
by X-ray background synthesis models. Furthermore, using the 6um continuum
luminosity to infer the intrinsic AGN luminosity and the stellar velocity
dispersion to estimate M_BH, we find that the most conservatively identified CT
AGNs in this sample may harbour some of the most rapidly growing black holes
(median M_BH~3x10^7M_o) in the nearby Universe, with a median Eddington ratio
of ~0.2.Comment: 16 pages, 2 tables, 6 figures. Accepted for publication in MNRA
The energy budget for X-ray to infrared reprocessing in Compton-thin and Compton-thick active galaxies
Heavily obscured active galactic nuclei (AGNs) play an important role in
contributing to the cosmic X-ray background (CXRB). However, the AGNs found in
deep X-ray surveys are often too weak to allow direct measurement of the column
density of obscuring matter. One method adopted in recent years to identify
heavily obscured, Compton-thick AGNs under such circumstances is to use the
observed mid-infrared to X-ray luminosity ratio as a proxy for the column
density. This is based on the supposition that the amount of energy lost by the
illuminating X-ray continuum to the obscuring matter and reprocessed into
infrared emission is directly related to the column density and that the proxy
is not sensitive to other physical parameters of the system (aside from
contamination by dust emission from, for example, star-forming regions). Using
Monte Carlo simulations, we find that the energy losses experienced by the
illuminating X-ray continuum in the obscuring matter are far more sensitive to
the shape of the X-ray continuum and to the covering factor of the X-ray
reprocessor than they are to the column density of the material. Specifically
we find that it is possible for the infrared to X-ray luminosity ratio for a
Compton-thin source to be just as large as that for a Compton-thick source even
without any contamination from dust. Since the intrinsic X-ray continuum and
covering factor of the reprocessor are poorly constrained from deep X-ray
survey data, we conclude that the mid-infrared to X-ray luminosity ratio is not
a reliable proxy for the column density of obscuring matter in AGNs even when
there is no other contribution to the mid-infrared luminosity aside from X-ray
reprocessing. This conclusion is independent of the geometry of the obscuring
matter.Comment: Accepted for publication in MNRAS. 12 pages, 7 figure
Early Science with the Large Millimeter Telescope: an energy-driven wind revealed by massive molecular and fast X-ray outflows in the Seyfert Galaxy IRAS 17020+4544
We report on the coexistence of powerful gas outflows observed in millimeter
and X-ray data of the Radio-Loud Narrow Line Seyfert 1 Galaxy IRAS 17020+4544.
Thanks to the large collecting power of the Large Millimeter Telescope, a
prominent line arising from the 12CO(1-0) transition was revealed in recent
observations of this source. The complex profile is composed by a narrow
double-peak line and a broad wing. While the double-peak structure may be
arising in a disk of molecular material, the broad wing is interpreted as the
signature of a massive outflow of molecular gas with an approximate bulk
velocity of -660 km/s. This molecular wind is likely associated to a
multi-component X-ray Ultra-Fast Outflow with velocities reaching up to ~0.1c
and column densities in the range 10^{21-23.9} cm^-2 that was reported in the
source prior to the LMT observations. The momentum load estimated in the two
gas phases indicates that within the observational uncertainties the outflow is
consistent with being propagating through the galaxy and sweeping up the gas
while conserving its energy. This scenario, which has been often postulated as
a viable mechanism of how AGN feedback takes place, has so far been observed
only in ULIRGs sources. IRAS 17020+4544 with bolometric and infrared luminosity
respectively of 5X10^{44} erg/s and 1.05X10^{11} L_sun appears to be an example
of AGN feedback in a NLSy1 Galaxy (a low power AGN). New proprietary
multi-wavelength data recently obtained on this source will allow us to
corroborate the proposed hypothesis.Comment: Accepted for publication on ApJ Letters, 9 pages, 4 figure
A discovery of young radio sources in the cores of giant radio galaxies selected at hard X-rays
Giant Radio Galaxies (GRG) are the largest single entities in the Universe,
having a projected linear size exceeding 0.7 Mpc, which implies that they are
also quite old objects. They are not common, representing a fraction of only
about 6% in samples of bright radio galaxies. While a census of about 300 of
these objects has been built in the past years, still no light has been shed on
the conditions necessary to allow such an exceptional growth, whether of
environmental nature or linked to the inner accretion properties. Recent
studies found that samples of radio galaxies selected from hard X-ray AGN
catalogs selected from INTEGRAL/IBIS and Swift/BAT (thus at energies >20 keV)
present a fraction of GRG four times larger than what found in radio-selected
samples. We present radio observations of 15 nuclei of hard X-ray selected GRG,
finding for the first time a large fraction (61%) of young radio sources at the
center of Mpc-scale structures. Being at the center of GRG, these young nuclei
may be undergoing a restarting activity episode, suggesting a link between the
detected hard X-ray emission - due to the ongoing accretion - and the
reactivation of the jets.Comment: Accepted for publication on Ap
Hard X-ray selected giant radio galaxies -- III. The LOFAR view
Giant radio galaxies (GRGs), with extended structures reaching hundreds of
kpc, are among the most spectacular examples of ejection of relativistic plasma
from super-massive black holes. In this work, third of a series, we present LOw
Frequency ARray (LOFAR) images at 144 MHz, collected in the framework of the
LOFAR Two-metre Sky Survey Data Release 2 (LoTSS DR2), for nine sources
extracted from our sample of hard X-ray selected GRGs (HXGRG, i.e. from
INTEGRAL/IBIS and Swift/BAT catalogues at >20 keV). Thanks to the resolution
and sensitivity of LoTSS, we could probe the complex morphology of these GRGs,
unveiling cases with diffuse (Mpc-scale) remnant emission, presence of faint
off-axis wings, or a misaligned inner jet. In particular, for one source
(B21144+35B), we could clearly detect a 300 kpc wide off-axis emission,
in addition to an inner jet which orientation is not aligned with the lobes
axis. For another source (J1153.9+5848) a structure consistent with jet
precession was revealed, appearing as an X-shaped morphology with relic lobes
having an extension larger than the present ones, and with a different axis
orientation. From an environment analysis, we found 2 sources showing an
overdensity of cosmological neighbours, and a correspondent association with a
galaxy cluster from catalogues. Finally, a comparison with radio-selected GRGs
from LoTSS DR1 suggested that, on average, HXGRG can grow to larger extents.
These results highlight the importance of deep low-frequency observations to
probe the evolution of radio galaxies, and ultimately estimate the duty cycle
of their jets.Comment: Accepted for publication in MNRA
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