1,470 research outputs found
The jet-disc connection in AGN
We present our latest results on the connection between accretion rate and
relativistic jet power in AGN, by using a large sample which includes mostly
blazars, but contains also some radio--galaxies. The jet power can be traced by
--ray luminosity in the case of blazars, and radio luminosity for both
classes. The accretion disc luminosity is instead traced by the broad emission
lines. Among blazars, we find a correlation between broad line emission and the
--ray or radio luminosities, suggesting a direct tight connection
between jet power and accretion rate. We confirm that the observational
differences between blazar subclasses reflect differences in the accretion
regime, but with blazars only we cannot properly access the low--accretion
regime. By introducing radio--galaxies, we succeed in observing the fingerprint
of the transition between radiatively efficient and inefficient accretion discs
in the jetted AGN family. The transition occurs at the standard critical value
and it appears smooth. Below this value, the
ionizing luminosity emitted by the accretion structure drops significantly.Comment: 11 pages, 6 figures. Accepted for publication in MNRA
The MURALES survey II. Presentation of MUSE observations of 20 3C low-z radio galaxies and first results
We present observations of a complete sub-sample of 20 radio galaxies from
the Third Cambridge Catalog (3C) with redshift <0.3 obtained from VLT/MUSE
optical integral field spectrograph. These data have been obtained as part of
the survey MURALES (a MUse RAdio Loud Emission line Snapshot survey) with the
main goal of exploring the Active Galactic Nuclei (AGN) feedback process in a
sizeable sample of the most powerful radio sources at low redshift. We present
the data analysis and, for each source, the resulting emission line images and
the 2D gas velocity field. Thanks to their unprecedented depth (the median 3
sigma surface brightness limit in the emission line maps is 6X10^-18 erg s-1
cm-2 arcsec-2, these observations reveal emission line structures extending to
several tens of kiloparsec in most objects. In nine sources the gas velocity
shows ordered rotation, but in the other cases it is highly complex. 3C sources
show a connection between radio morphology and emission line properties.
Whereas, in three of the four Fanaroff and Riley Class I radio galaxies (FRIs),
the line emission regions are compact, ~1 kpc in size; in all but one of the
Class II radiogalaxies FRIIs, we detected large scale structures of ionized gas
with a median extent of 17 kpc. Among the FRIIs, those of high and low
excitation show extended gas structures with similar morphological properties,
suggesting that they both inhabit regions characterized by a rich gaseous
environment on kpc scale.Comment: Accepted for publication in A&
The MURALES survey. I. A dual AGN in the radio galaxy 3C459?
We observed the FRII radio galaxy 3C459 (z=0.22) with the MUSE spectrograph
at the Very Large Telescope (VLT) as part of the MURALES project (a MUse RAdio
Loud Emission line Snapshot survey). We detected diffuse nuclear emission and a
filamentary ionized gas structure forming a one-sided, triangular-shaped region
extending out to 80 kpc. The central emission line region is dominated by
two compact knots of similar flux: the first (N1) cospatial with the radio core
and the (N2) second located 1.2" (5.3 kpc) to the SE. The two regions differ
dramatically from the point of view of velocity (with an offset of ~400 km/s),
line widths, and line ratios. This suggests that we are observing a dual AGN
system formed by a radio loud AGN and type 2 QSO companion, which is the result
of the recent merger that also produced its disturbed host morphology. The
alternative possibility that N2 is just a bright emission line knot resulting
from, for example, a jet-cloud interaction, is disfavored because of 1) the
presence of a high ionization bicone whose apex is located at N2; 2) the
observed narrow line widths; 3) its line luminosity (~10^42 erg s-1) typical of
luminous QSOs; and 4) its location, which is offset from the jet path. The
putative secondary AGN must be highly obscured, since we do not detect any
emission in the Chandra and infrared Hubble Space Telescope images.Comment: 6 pages, 6 figures, A&A in pres
An optical spectroscopic survey of the 3CR sample of radio galaxies with z<0.3. III. Completing the sample
We present optical nuclear spectra for nine 3CR radio sources obtained with
the Telescopio Nazionale Galileo, that complete our spectroscopic observations
of the sample up to redshifts 0.3. We measure emission line luminosities
and ratios, and derive a spectroscopic classification for these sources.Comment: Accepted for publication in A&A. We provide as additional material
two tables presenting the main data for the whole sample, combining the
results presented here with those of Paper I and Paper I
A survey of Low Luminosity Compact sources and its implication for evolution of radio-loud AGNs. II. Optical analysis
This is the second in a series of papers concerning a new sample of low
luminosity compact (LLC) objects. Here we discuss the optical properties of the
sample based on Sloan Digital Sky Survey (SDSS) images and spectra. We have
generated different diagnostic diagrams and classified the sources as high and
low excitation galaxies (HEG and LEG, respectively). We have studied the
jet-host interactions, relation between radio and optical line emission and
evolution of the radio source within a larger sample that included also the
published samples of compact steep spectrum (CSS), gigahertz peaked spectrum
(GPS) sources and FRII and FRI objects. The optical and radio properties of the
LLC sample are in general consistent with brighter CSS and large-scale radio
sources, although the LLC objects have lower values of [OIII] luminosity than
the more powerful CSS sources (L_1.4GHz>10^25 W/Hz). However, when LLC are
added to the other samples, HEG and LEG seem to follow independent, parallel
evolutionary tracks. Regarding ionization mechanisms, LLC and luminous CSS
objects behave like FRII sources, while FRI seem to belong to a different group
of objects. Based on our results, we propose the independent, parallel
evolutionary tracks for HEG and LEG sources, evolving from GPS - CSS - FR.Comment: 12 pages, 2 figures, 2 tables, MNRAS in pres
The Molecular Gas Content of z<0.1 Radio Galaxies: Linking the AGN Accretion Mode to Host Galaxy Properties
One of the main achievements in modern cosmology is the so-called `unified
model', which successfully describes most classes of active galactic nuclei
(AGN) within a single physical scheme. However, there is a particular class of
radio-luminous AGN that presently cannot be explained within this framework --
the `low-excitation' radio AGN (LERAGN). Recently, a scenario has been put
forward which predicts that LERAGN, and their regular `high-excitation' radio
AGN (HERAGN) counterparts represent different (red sequence vs. green valley)
phases of galaxy evolution. These different evolutionary states are also
expected to be reflected in their host galaxy properties, in particular their
cold gas content. To test this, here we present CO(1-0) observations toward a
sample of 11 of these systems conducted with CARMA. Combining our observations
with literature data, we derive molecular gas masses (or upper limits) for a
complete, representative, sample of 21 z<0.1 radio AGN. Our results yield that
HERAGN on average have a factor of ~7 higher gas masses than LERAGN. We also
infer younger stellar ages, lower stellar, halo, and central supermassive black
masses, as well as higher black hole accretion efficiencies in HERAGN relative
to LERAGN. These findings support the idea that high- and low-excitation radio
AGN form two physically distinct populations of galaxies that reflect different
stages of massive galaxy build-up.Comment: 8 pages, 4 figures, 4 tables; accepted for publication in Ap
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