1,273 research outputs found
The ATESP 5 GHz radio survey IV. 19, 38, and 94 GHz observations and radio spectral energy distributions
It is now established that the faint radio population is a mixture of
star-forming galaxies and faint active galactic nuclei (AGNs), with the former
dominating below S(1.4GHz) \sim 100 muJy and the latter at larger flux
densities. The faint radio AGN component can itself be separated into two main
classes, mainly based on the host-galaxy properties: sources associated with
red/early-type galaxies (like radio galaxies) are the dominant class down to
\sim 100 muJy; quasar/Seyfert--like sources contribute an additional 10-20\%.
One of the major open questions regarding faint radio AGNs is the physical
process responsible for their radio emission. This work aims at investigating
this issue, with particular respect to the AGN component associated with
red/early-type galaxies. Such AGNs show, on average, flatter radio spectra than
radio galaxies and are mostly compact (<= 30 kpc in size). Various scenarios
have been proposed to explain their radio emission. For instance they could be
core/core-jet dominated radio galaxies, low-power BL LACs, or
advection-dominated accretion flow (ADAF) systems. We used the Australia
Telescope Compact Array (ATCA) to extend a previous follow-up multi-frequency
campaign to 38 and 94 GHz. (abridged)Comment: 16 pages, 7 figures, 6 tables. Accepted for publication in A&
The core fundamental plane of B2 radio galaxies
The photometric, structural and kinematical properties of the centers of
elliptical galaxies, harbor important information of the formation history of
the galaxies. In the case of non active elliptical galaxies these properties
are linked in a way that surface brightness, break radius and velocity
dispersion of the core lie on a fundamental plane similar to that found for
their global properties. We construct the Core Fundamental Plane (CFP) for a
sizeable sample of low redshift radio galaxies and compare it with that of non
radio ellipticals. To pursue this aim we combine data obtained from high
resolution HST images with medium resolution optical spectroscopy to derive the
photometric and kinematic properties of ~40 low redshift radio galaxies. We
find that the CFPs of radio galaxies is indistinguishable from that defined by
non radio elliptical galaxies of similar luminosity. The characteristics of the
CFP of radio galaxies are also consistent (same slope) with those of the
Fundamental Plane (FP) derived from the global properties of radio (and non
radio) elliptical galaxies. The similarity of CFP and FP for radio and non
radio ellipticals suggests that the active phase of these galaxies has minimal
effects for the structure of the galaxies.Comment: 8 pages, 4 figures, accepted for publication in Astronomy and
Astrophysic
The ATESP 5 GHz radio survey. II. Physical properties of the faint radio population
One of the most debated issues about sub-mJy radio sources, which are
responsible for the steepening of the 1.4 GHz source counts, is the origin of
their radio emission. Particularly interesting is the possibility of combining
radio spectral index information with other observational properties to assess
whether the sources are triggered by star formation or nuclear activity. The
aim of this work is to study the optical and near infrared properties of a
complete sample of 131 radio sources with S>0.4 mJy, observed at both 1.4 and 5
GHz as part of the ATESP radio survey. We use deep multi-colour (UBVRIJK)
images, mostly taken in the framework of the ESO Deep Public Survey, to
optically identify and derive photometric redshifts for the ATESP radio
sources. Deep optical coverage and extensive colour information are available
for 3/4 of the region covered by the radio sample. Typical depths of the images
are U~25, B~26, V~25.4, R~25.5, I~24.3, 19.5<K_s<20.2, J<22.2. Optical/near
infrared counterparts are found for ~78% (66/85) of the radio sources in the
region covered by the deep multi-colour imaging, and for 56 of these reliable
estimates of the redshift and type are derived. We find that many of the
sources with flat radio spectra are characterised by high radio-to-optical
ratios (R>1000), typical of classical powerful radio galaxies and quasars.
Flat-spectrum sources with low R values are preferentially identified with
early type galaxies, where the radio emission is most probably triggered by
low-luminosity active galactic nuclei. Considering both early type galaxies and
quasars as sources with an active nucleus, such sources largely dominate our
sample (78%). Flat-spectrum sources associated with early type galaxies are
quite compact (d<10-30 kpc), suggesting core-dominated radio emission.Comment: 15 pages, 13 figures, accepted for pubblication in A&
The ATESP Radio Survey II. The Source Catalogue
This paper is part of a series reporting the results of the Australia
Telescope ESO Slice Project (ATESP) radio survey obtained at 1400 MHz with the
Australia Telescope Compact Array (ATCA) over the region covered by the ESO
Slice Project (ESP) galaxy redshift survey. The survey consists of 16 radio
mosaics with ~8"x14" resolution and uniform sensitivity (1sigma noise level ~79
microJy) over the whole area of the ESP redshift survey (~26 sq. degrees at
decl. -40 degr). Here we present the catalogue derived from the ATESP survey.
We detected 2960 distinct radio sources down to a flux density limit of ~0.5
mJy (6sigma), 1402 being sub-mJy sources. We describe in detail the procedure
followed for the source extraction and parameterization. The internal accuracy
of the source parameters was tested with Monte Carlo simulations and possible
systematic effects (e.g. bandwidth smearing) have been quantified.Comment: 14 pages, 14 Postscript figures, Accepted for publication in A&A
Suppl. Corrected typos and added Journal Referenc
In search of dying radio sources in the local universe
Up till now very few dying sources were known, presumably because the dying
phase is short at centimeter wavelengths. We therefore have tried to improve
the statistics on sources that have ceased to be active, or are intermittently
active. The latter sources would partly consist of a fossil radio plasma left
over from an earlier phase of activity, plus a recently restarted core and
radio jets. Improving the statistics of dying sources will give us a better
handle on the evolution of radio sources, in particular the frequency and time
scales of radio activity. We have used the WENSS and NVSS surveys, in order to
find sources with steep spectral indices, associated with nearby elliptical
galaxies. In the cross correlation we presently used only unresolved sources,
with flux densities at 1.4 GHz larger than 10 mJy. The eleven candidates thus
obtained were observed with the VLA in various configurations, in order to
confirm the steepness of the spectra, and to check whether active structures
like flat-spectrum cores and jets are present, perhaps at low levels. We
estimated the duration of the active and relic phases by modelling the
integrated radio spectra using the standard models of spectral evolution. We
have found six dying sources and three restarted sources, while the remaining
two candidates remain unresolved also with the new VLA data and may be Compact
Steep Spectrum sources, with an unusually steep spectrum. The typical age of
the active phase, as derived by spectral fits, is in the range 10^7 - 10^8
years. For our sample of dying sources, the age of the relic phase is on
average shorter by an order of magnitude than the active phase.Comment: 21 pages, 17 figures, accepted by A&A. For a version with high
quality figures, see http://erg.ca.astro.it/preprints/dying2007
HST images of B2 radio galaxies: the link between circum-nuclear dust and radio properties
We discuss HST images in V and I of radio galaxies selected from the B2
sample of low luminosity radio galaxies. Absorption maps were constructed which
highlight the presence of circumnuclear dust on scales of typically few kpc or
less.Comment: 4 pages, 4 figures, in "The Central kpc of Starbursts and AGN: The La
Palma Connection", ASP Conf Series, in press, eds J.H. Knapen, J.E. Beckman,
I. Shlosman and T.J. Mahone
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