241 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&
Parsec-scale morphology and spectral index distribution in faint high frequency peakers
We investigate the parsec-scale structure of 17 high frequency peaking radio
sources from the faint HFP sample. VLBA observations were carried out at two
adjacent frequencies, 8.4 and 15.3 GHz, both in the optically-thin part of the
spectrum, to obtain the spectral index information. We found that 64% of the
sources are resolved into subcomponents, while 36% are unresolved even at the
highest frequency. Among the resolved sources, 7 have a morphology and a
spectral index distribution typical of young radio sources, while in other 4
sources, all optically associated with quasars, the radio properties resemble
those of the blazar population. The equipartition magnetic field of the single
components are a few tens milliGauss, similar to the values found in the
hotspots of young sources with larger sizes. Such high magnetic fields cause
severe radiative losses, precluding the formation of extended lobe structures
emitting at centimeter wavelengths. The magnetic fields derived in the various
components of individual source are usually very different, indicating a non
self-similar source evolution, at least during the very first stages of the
source growth.Comment: 14 pages, 5 figures, accepted for publication in MNRA
HI absorption towards nearby compact radio sources
We present the results of HI absorption measurements towards a sample of
nearby Compact Steep-Spectrum (CSS) and Giga-Hertz Peaked Spectrum (GPS) radio
sources, the CORALZ sample, using the Giant Metrewave Radio Telescope (GMRT).
We observed a sample of 18 sources and find 7 new detections. These sources are
of lower luminosity than earlier studies of CSS and GPS objects and we
investigate any dependence of HI absorption features on radio luminosity.
Within the uncertainties, the detection rates and column densities are similar
to the more luminous objects, with the GPS objects exhibiting a higher
detection rate than for the CSS objects. The relative velocity of the
blueshifted absorption features, which may be due to jet-cloud interactions,
are within 250 km s and do not appear to extend to values over
1000 km s seen for the more luminous objects. This could be due to the
weaker jets in these objects, but requires confirmation from observations of a
larger sample of sources. There appears to be no evidence of any dependence of
HI column density on either luminosity or redshift, but these new detections
are consistent with the inverse relation between HI column density and
projected linear size.Comment: 10 pages, 6 figures, accepted for publication in MNRA
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