192 research outputs found
Environment of compact extragalactic radio sources
We have studied the interrelation of young AGN with their hosts. The objects
of study are the young and powerful GPS and CSS radio sources. Due to their
small size, GPS and CSS sources are excellent probes of this relation.
Furhthermore, their young age allows us to compare them to the larger, old
radio sources and establish a time-line evolution of this relation. Combining
imaging and spectroscopy at UV, optical and radio wavelengths we find evidence
of strong interaction between the host and the radio source. The presence and
expansion of the radio source clearly affects the properties and evolution of
the host. Furthermore, the radio source and host significantly affect each
other's evolution. We describe our results and how these interactions take
place.Comment: 6 pages. To appear in "Highlights of Spanisg astrophysics IV.
Proceedings of the VII scientific meeting of the Spanish Astronomical
Society". Editors: F. Figueras, J.M. Girart, M.Hernanz, C. Jordi. Springe
The B3-VLA CSS sample. VIII: New optical identifications from the Sloan Digital Sky Survey. The ultraviolet-optical spectral energy distribution of the young radio sources
Compact steep-spectrum radio sources and giga-hertz peaked spectrum radio
sources (CSS/GPS) are generally considered to be mostly young radio sources. In
recent years we studied at many wavelengths a sample of these objects selected
from the B3-VLA catalog: the B3-VLA CSS sample. Only ~ 60 % of the sources were
optically identified. We aim to increase the number of optical identifications
and study the properties of the host galaxies of young radio sources. We
cross-correlated the CSS B3-VLA sample with the Sloan Digital Sky Survey
(SDSS), DR7, and complemented the SDSS photometry with available GALEX (DR 4/5
and 6) and near-IR data from UKIRT and 2MASS. We obtained new identifications
and photometric redshifts for eight faint galaxies and for one quasar and two
quasar candidates. Overall we have 27 galaxies with SDSS photometry in five
bands, for which we derived the ultraviolet-optical spectral energy
distribution (UV-O-SED). We extended our investigation to additional CSS/GPS
selected from the literature. Most of the galaxies show an excess of
ultra-violet (UV) radiation compared with the UV-O-SED of local radio-quiet
ellipticals. We found a strong dependence of the UV excess on redshift and
analyzed it assuming that it is generated either from the nucleus (hidden
quasar) or from a young stellar population (YSP). We also compare the UV-O-SEDs
of our CSS/GPS sources with those of a selection of large size (LSO) powerful
radio sources from the literature. If the major process of the UV excess is
caused by a YSP, our conclusion is that it is the result of the merger process
that also triggered the onset of the radio source with some time delay. We do
not see evidence for a major contribution from a YSP triggered by the radio
sources itself.Comment: 38 pages, 21 figures, 6 tables. Accepted for publication on A&
Star formation in the hosts of GHz peaked spectrum and compact steep spectrum radio galaxies
AIMS: Search for star formation regions in the hosts of potentially young
radio galaxies (Gigahertz Peaked Spectrum and Compact Steep Spectrum sources).
METHODS: Near-UV imaging with the Hubble Space Telescope Advanced Camera for
Surveys.} RESULTS: We find near-UV light which could be the product of recent
star formation in eight of the nine observed sources, though other explanations
are not currently ruled out. The UV luminosities of the GPS and CSS sources are
similar to those of a sample of nearby large scale radio galaxies. Stellar
population synthesis models are consistent with a burst of recent star
formation occuring before the formation of the radio source. However,
observations at other wavelengths and colors are needed to definitively
establish the nature of the observed UV light. In the CSS sources 1443+77 and
1814-637 the near-UV light is aligned with and is co-spatial with the radio
source. We suggest that in these sources the UV light is produced by star
formation triggered and/or enhanced by the radio source.Comment: 14 pages, 11 figs. Accepted to A&A. Paper with high resolution images
can be found at
http://damir.iem.csic.es/extragalactic/publications/publications.htm
Star formation in z>1 3CR host galaxies as seen by Herschel
We present Herschel (PACS and SPIRE) far-infrared (FIR) photometry of a
complete sample of z>1 3CR sources, from the Herschel GT project The Herschel
Legacy of distant radio-loud AGN (PI: Barthel). Combining these with existing
Spitzer photometric data, we perform an infrared (IR) spectral energy
distribution (SED) analysis of these landmark objects in extragalactic research
to study the star formation in the hosts of some of the brightest active
galactic nuclei (AGN) known at any epoch. Accounting for the contribution from
an AGN-powered warm dust component to the IR SED, about 40% of our objects
undergo episodes of prodigious, ULIRG-strength star formation, with rates of
hundreds of solar masses per year, coeval with the growth of the central
supermassive black hole. Median SEDs imply that the quasar and radio galaxy
hosts have similar FIR properties, in agreement with the orientation-based
unification for radio-loud AGN. The star-forming properties of the AGN hosts
are similar to those of the general population of equally massive non-AGN
galaxies at comparable redshifts, thus there is no strong evidence of universal
quenching of star formation (negative feedback) within this sample. Massive
galaxies at high redshift may be forming stars prodigiously, regardless of
whether their supermassive black holes are accreting or not.Comment: 30 pages, 13 figures, 4 tables. Accepted for publication in A&
The number counts, luminosity functions and evolution of microwave-selected (WMAP) blazars and radio galaxies
(Abridged) We carried out an extensive search to identify the counterparts of
all the sources listed in the WMAP 3-yr catalogue using literature and archival
data. Our work led to the identification of 309 WMAP sources, 98% of which are
blazars, radio quasars or radio galaxies. At present, 15 objects still remain
without identification due to the lack of optical spectroscopic data or a clear
radio counterpart. Our results allow us to define a flux limited sample of 203
high Galactic latitude microwave sources ( Jy, ) which is virtually completely identified (99%). The microwave band
is ideally suited for blazar statistical studies since this is the part of the
em spectrum that is least affected by the superposition of spectral components
of different origin. Using this data-set we derived number counts, luminosity
functions and cosmological evolution of blazars and radio galaxies at microwave
frequencies. Our results are in good agreement with those found at radio
frequencies. The 5 GHz bivariate blazar luminosity functions are similar to
those derived from the DXRBS survey, which shows that this sample is
representative of the blazar population at 41 GHz. Microwave selected broad-
lined quasars are about 6 times more abundant than BL Lacs, a ratio that is
similar to, or larger than, that seen at radio and gamma-ray frequencies, once
spectral selection effects are taken into account. This strongly suggests that
the mechanism responsible for the generation of gamma-rays is, at first order,
the same in all blazar types. Our results confirm the findings of Giommi &
Colafrancesco (2004, 2006) that blazars and radio galaxies are the largest
contaminants of the CMB anisotropy maps. We predict that these sources are also
bright gamma-ray sources, most of which will be detected by AGILE and FERMI.Comment: 18 pages, 11 figures, 3 tables. A&A in pres
On the spectro-photometric properties of the bulk of the radio-loud AGN population
In a previous paper we showed that the radio sources selected by combining
large areas radio and optical surveys, present a strong deficit of radio
emission with respect to 3CR radio-galaxies matched in line emission
luminosity. We argued that the prevalence of sources with luminous extended
radio structures in high flux limited samples is due to a selection bias.
Sources with low radio power form the bulk of the radio-loud AGN population but
are still virtually unexplored.
We here analyze their photometric and spectroscopic properties. From the
point of view of their emission lines, the majority of the sample are Low
Excitation Galaxies (LEG), similar to the 3CR objects at the same level of line
luminosity. The hosts of LEG are red, massive Early-Type Galaxies (ETG) with
large black holes masses , statistically indistinguishable from the hosts of
low redshift 3CR/LEG sources. No genuine radio-loud LEG could be found
associated with black holes with a mass substantially lower than 10^8 M(sun) or
with a late type host. The fraction of galaxies with signs of star formation
(5%) is similar to what is found in both the quiescent ETG and 3CR/LEG hosts.
We conclude that the deficit in radio emission cannot be ascribed to
differences in the properties of their hosts. We argue that instead this could
be due to a temporal evolution of the radio luminosity.
A minority (10%) of the sample show rather different properties, being
associated with low black hole masses, with spiral galaxies, or showing a high
excitation spectrum. In general these outliers are the result of the
contamination from Seyfert and from galaxies where the radio emission is
powered by star formation. For the objects with high excitation spectra there
is no a clear discontinuity in either the host or nuclear properties as they
span from radio-quiet and radio-loud AGN.Comment: Accepted for publication in A&
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