996 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 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
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&
Global cropland and greenhouse gas impacts of UK food supply are increasingly located overseas
Funding This work was supported by a University of Aberdeen Environment and Food Security Theme/the James Hutton Institute PhD studentship, and contributes to the Scottish Food Security Alliance-Crops and the Belmont Forum supported DEVIL project (NERC fund UK contribution: NE/M021327/1). J.M. and R.B.M. acknowledge funding from the Rural and Environment Science and Analytical Services, Scottish Government. T.K. acknowledges funding from the European Research Council Grant ERC-263522 (LUISE).Peer reviewedPostprin
Automated optical identification of a large complete northern hemisphere sample of flat spectrum radio sources with S_6cm > 200 mJy
This paper describes the automated optical APM identification of radio
sources from the Jodrell Bank - VLA Astrometric Survey (JVAS), as used for the
search for distant radio-loud quasars. The sample has been used to investigate
possible relations between optical and radio properties of flat spectrum radio
sources. From the 915 sources in the sample, 756 have an optical APM
identification at a red (e) and/or blue (o) plate,resulting in an
identification fraction of 83% with a completeness and reliability of 98% and
99% respectively. About 20% are optically identified with extended APM objects
on the red plates, e.g. galaxies. However the distinction between galaxies and
quasars can not be done properly near the magnitude limit of the POSS-I plates.
The identification fraction appears to decrease from >90% for sources with a 5
GHz flux density of >1 Jy, to <80% for sources at 0.2 Jy. The identification
fraction, in particular that for unresolved quasars, is found to be lower for
sources with steeper radio spectra. In agreement with previous studies, we find
that the quasars at low radio flux density levels also tend to have fainter
optical magnitudes, although there is a large spread. In addition, objects with
a steep radio-to-optical spectral index are found to be mainly highly polarised
quasars, supporting the idea that in these objects the polarised synchrotron
component is more prominent. It is shown that the large spread in
radio-to-optical spectral index is possibly caused by source to source
variations in the Doppler boosting of the synchrotron component [Abridged].Comment: LaTex, 17 pages, 5 gif figures, 4 tables. Accepted for publication in
MNRAS. High resolution figures can be found at http://www.roe.ac.uk/~ignas
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