[ CATS home ] [ Back to CATS list ]
[ ftp ]
1999MNRAS.302..222Ciliegi+
See also ELAIS Southern survey with ATCA
Deep VLA 20cm survey of the ISO ELAIS survey regions
from http://www.ast.cam.ac.uk/elais/vla/ on 25-Jan-99
THE RADIO CATALOGUE
The catalogue contains 867 sources, 44 of which have multiple component for
a total of 921 components. The catalogue reports the name of the sources,
the peak flux density Sp (mJy/beam), the total flux density SI in mJy, the
RA and DEC (J2000), the FWHM of the major and minor axis (in arcsec), the
positional angle of the major axis in degree and the off-axis value in the
VLA map (in arcmin). The different components of multiple sources are
labeled A, B, ... followed by a line labeled T in which flux and position of
the total sources are give.
A detailed description of the catalogue is reported in the paper A Deep VLA
survey at 20cm of the ISO ELAIS survey regions by Ciliegi et al. 1999,
MNRAS, 302, 222.
Here there is an ascii table with the full catalogue.
Paolo Ciliegi ciliegi@ast.cam.ac.uk
Last modified: Mon Jan 25 12:17:06 1999
Below text from author's TEX-file:
1999MNRAS.302..222Ciliegi+
A Deep VLA survey at 20cm of the ISO ELAIS survey regions
P. Ciliegi, R.G. McMahon, G. Miley, C. Gruppioni,
M. Rowan-Robinson, C. Cesarsky, L. Danese, A. Franceschini,
R. Genzel, A. Lawrence, D. Lemke, S. Oliver, J-L. Puget, B. Rocca-Volmerange
Abstract
We have used the Very Large Array(VLA) in C configuration to carry
out a sensitive 20cm radio survey of regions of sky that have been
surveyed in the Far Infra-Red over the wavelength range 5-200 microns
with ISO as part of the European Large Area ISO Survey(ELAIS). As
usual in surveys based on a relatively small number of overlapping
VLA pointings the flux limit varies over the area surveyed. The
survey has a flux limit that varies from a 5-sigma limit
of 0.135mJy over an area
of 0.12deg^2 to a 5-sigma limit of 1.15mJy or better over the whole
region covered of 4.22 deg^2. In this paper we present
the radio catalogue of 867 sources. These regions of sky have
previously been surveyed to shallow flux limits at 20cm with the
VLA as part of the VLA D configuration NVSS(FWHM=45 arcsec) and
VLA B configuration FIRST(FWHM=5 arcsec) surveys. Our whole survey
has a nominal 5 sigma flux limit a factor of 2 below that of
the NVSS; 3.4 deg^2 of the survey reaches the nominal flux
limit of the FIRST
survey and 1.5 deg^2 reaches to 0.25 mJy, a factor of 3 below the nominal
FIRST survey limit. In addition our survey is at
resolution intermediate between the two surveys and thus
is well suited for a comparison of the reliability and
resolution dependent surface brightness effects that
affect interferometric radio surveys.
We have carried out a detailed comparison of the reliability
of our own survey and these two independent surveys in order to assess the
reliability and completeness of each survey.
Introduction
The Infrared Space Observatory (ISO, Kessler et al. 1996),
launched in November 1995 was
the successor of the Infrared Astronomical Satellite (IRAS)
and provided unparallel sensitivity in mid to
far infrared wavelengths ($i.e.$ 5--200 $\mu m$). The European Large-Area
ISO Survey (ELAIS, Oliver et al. 1997, Oliver et al. 1998 in preparation)
is a project that used ISO to carry out a deep wide angle survey
at wavelengths of 6.7, 15, 90 and 175 $\mu m$. The 6.7 and 15 $\mu m$ surveys
were carried out with the
ISO-CAM camera (Cesarsky et al. 1996) with the aim to reach a
5$\sigma$ sensitivity of $\sim$2mJy at 15microns.
The $90\mu m$ and 175$\mu m$ surveys used the
ISO-PHOT camera (Lemke et al. 1994) with the aim to reach a 5$\sigma$
sensitivity of $\sim$25mJy.
At these limits, we expect ISO to be confusion limited
at 90 $\mu m$ and 175 $\mu m$ by galaxies and
galactic cirrus emission and hence this survey should be the deepest FIR
survey possible with the satellite.
The area covered in the ELAIS survey is
$\sim 13$ square degrees at 15 and 90 microns, $\sim 7$ square degrees
at 6.7 microns and $\sim 3$ square degrees at 175microns.
The ELAIS survey is $\sim$50 times deeper at
5-20$\mu m$ than IRAS. Thus our survey will allow us to explore
IRAS-like populations to higher redshift and possibly unveil
new classes of objects or unexpected phenomena.
We expect to detect thousands of galaxies, many of
which will be at high redshifts and undergoing vigorous star formation.
The expected large number of high-z IR galaxies
should provide vital information about the star formation rate
out to z=1 and possibly earlier.
The spatial resolution of ISO will be insufficient to properly
identify optically faint objects. At 15 microns, the survey resolution is
$\sim$ 10 arcsec and at 90 microns it will be about one arc minute.
Complementary radio data will play a crucial role in identifying many of
the most interesting objects, as they did in the early days of X-ray
astronomy (e.g. Cyg X-1) and in more recent times for IRAS (e.g.
IRAS F10214+4714 (Rowan-Robinson et al. 1991).
In this paper we report the description of the radio observations
obtained in the three ISO-ELAIS survey regions in the northern
celestial hemisphere (N1\_1610+5430, N2\_1636+4115 and N3\_1429+3306).
The observations are made with the Very Large Array (VLA) radio telescope
at 1.4GHz (20cm) in the VLA C-configuration (maximum baseline 11km)
with a resolution (FWHM) of $\sim15$ arcsec. The aim of these VLA
observation was to obtain an uniform covering of the ELAIS regions with
a rms noise limit of $\sim$50 $\mu$Jy.
These VLA
observations will be essential in the optical identification phase
of the ELAIS sources and in assessing the reliability of the
ELAIS source lists.
Moreover, with a radio survey it will be possible to investigate
the radio/far--infrared correlation in star forming galaxies to flux
densities deeper than those reached by IRAS. Helou, Sofier \& Rowan-Robinson
(1985) noted a strong correlation between radio and far infrared flux
for star forming galaxies, valid over a very wide range of infrared
luminosities, and this has been confirmed in many other studies
(e.g. Wunderlich, Klein \& Wielebinski 1987; Condon, Anderson \& Helou
1991). The radio emission is interpreted as a synchrotron radiation
from relativistic electron which have leaked out of supernova remnants.
It is expected that this correlation should extend below the IRAS flux
level since the majority of the sub-mJy radio sources have been identified
with faint blue galaxies whith spectra similar to those of star forming
objects (Benn et al. 1993).
In addition, combining deep radio and optical data with the ISO survey
fluxes will provide information on the trivariate IR-radio-optical
luminosity function and its evolution and the contribution of
starburst galaxies to the sub-mJy radio source counts. The ratio of
the FIR emission and radio emission will also allow is to investigate
the physical origin and spatial distribution of the energy sources in
the detected objects in the same way that VLA maps have been central
to our understanding of the origin of IRAS sources.
Finally, this survey, due to its depth and extension, is very
important also as radio survey in its own right. In fact, the selected sample
is large and deep enough to constitute a statistically significant
sample of sub-mJy radio sources, whose nature and characteristics
are still a major topic in observational cosmology (see Windhorst,
Mathis \& Neuschaefer 1990, Fomalont et al. 1991, Rowan-Robinson
et al. 1993, Gruppioni et al. 1997)
Radio observations
Choice of observing frequency and VLA configuration
The VLA C--configuration and the observing frequency of 1.4 GHz
give the optimum resolution to acquire the kind
of radio data that we need. Whilst less prone to surface brightness
effects , the VLA D configuration is confusion-limited at the fluxes
we wish to attain (the 5 $\sigma$ confusion limit in D configuration
is 0.4 mJy/beam). With the C configuration and a frequency of 1.4 GHz
the synthesized beam size (Full Width at Half Power, FWHP) is $\sim$15
arcsec. The well-defined synthesized beam of the VLA should enable us
to pinpoint optical identifications to 1 arcsec,
except for the asymmetric multi-components sources.
The frequency of 1.4 GHz was chosen because at this
frequency the FWHP of the VLA primary beam is
31 arcmin. This allow us to cover the ELAIS field with a relative
small number of pointing centers. In fact it is possible to obtain a
mosaic map with nearly uniform sensitivity if the separation is 31 /
$\sqrt{2}$ $\sim$ 22 arcmin. Moreover, at 1.4 GHz there will be
contributions from both the steep and flat spectrum population of
radio sources.
....
The Source Catalogue
Considering all the available observations we detected a total of
867 sources at $\geq$ 5 $\sigma$ level (44 of which have multiple
components) over a total area of 4.222 deg$^2$. The catalogue with all
the 867 sources (921 components) reports the name of the source, the
peak flux density S$_P$ in mJy, the total flux density S$_I$ in mJy,
the RA and DEC (J2000), the full width half maximum (FWHM) of the
major and minor axes $\theta_M$ and $\theta_m$ (in arcsec), the positional
angle PA of the major axis (in degrees) and the off-axis values in the
VLA map (in arcmin).
The different components of multiple sources are labeled ``A'', ``B'',
etc., followed by a line labeled ``T'' in which flux and position
for the total sources are given. For these total sources the
position have been computed as the
flux-weighted average position for all the components.
Table 3 shows the first
page of the catalogue as an example.
....
Summary
Using the Very Large Array (VLA) radio telescope, we observed at 1.4
GHz a total area of 4.222 deg$^2$ in the ISO/ELAIS regions N1 N2 and N3.
The lower flux density limit reached by our observation is 0.135 mJy
(at 5 $\sigma$ level) on an area of 0.118 deg$^2$, while the bulk of
the observed regions are mapped with a flux density limit of 0.250
mJy (5 $\sigma$). The data were analyzed using the NRAO {\tt AIPS}
reduction package. The source extraction has been carried out with
the {\tt AIPS} task {\tt SAD}. The reliability of {\tt SAD} has been tested
using the maps of the radio surveys $FIRST$ and $NVSS$.
Considering all the available observations, we detected a total of
867 sources at 5 $\sigma$ level, 44 of which have multiple components.
These sources were used to calculate the normalized differential source
counts. They provide a check on catalogue completeness and reliability
plus information about source evolution.
A comparison with other surveys shows a very good agreement,
confirming the presence of the well-know flattening of the counts
below 1 mJy, the completeness of our catalogue and the reliability
of our procedure for the source extraction.
A comparison with the $FIRST$ and $NVSS$ radio surveys has confirmed
the incompleteness of these two surveys near their flux limits, while a
flux comparison between the three surveys has shown that our survey
with the VLA array in C configuration is the best compromise between
high and low resolution radio surveys. The positional errors of the
radio sources are $\sim$ 2 arcsec for the fainter sources
($\sim$0.13 mJy) and $\sim$ 0.6 arcsec for the brighter sources ($>$ 10 mJy).
This small value will enable us to obtain an accurate and fast
optical/infrared identification of the radio sources.
Bibliography
Benn C.R., Rowan-Robinson M., McMahon R.G., Broadhurst T.J.
\& Lawrence A., 1993, MNRAS, 263, 98
Cesarsky et al. 1996, A\&A, 315, L32
Condon J.J., Condon M.A. and Hazard C., 1982, AJ, 87, 739
Condon J.J. \& Mitchell K.J., 1984, AJ, 89, 610
Condon J.J, Anderson M.L. \& Helou G., 1991, ApJ, 376, 95
Condon J.J, et al., 1993, AAS, 183, 640
Condon J.J., 1997, PASP, 109, 166
Condon J.J. et al. 1998, in preparation
Fomalont E.B.,Windhorst R.A., Kristian J.A. \& Kellerman K.I.,
1991, AJ, 102, 1258.
Gruppioni C., Zamorani G., de Ruiter H.R., Parma P., Mignoli M \&
Lari C., 1997, MNRAS, 286, 470
Helou G, Sofier B.T. \& Rowan-Robinson M., 1985, ApJ, 298, L7
Kessler M.F. et al. 1996, A\&A, 315, L27
Kleinmann et al., 1988, ApJ, 328, 161
Lemke D. et al. 1994, {\em ISOPHOT Observer's manual}, ed.
U. Klaas, H. Krueger, I. Heinrichsen, A. Heske, R. Laureijs; Pubs: ESA
Mitchell K.J. \& Condon J.J, 1985,AJ, 90, 1957
Oliver S. et al. 1997, {\em IAU 179 New Horizons from
Multi-Wavelength Sky Surveys}, ed: B. McLean; Pubs: Kluwer, in press
Perley R.A., 1989, in {\it Synthesis Imaging in Radio Astronomy},
edit by R.A. Perley, F.R. Schwab \& A.H. Bridle (ASP, San Francisco), p. 259
Rowan-Robinson M. et al. 1991, Nature, 351, 719
Rowan-Robinson M., Benn C.R., Lawrence A., McMahon R.G. \&
T.J., 1993, MNRAS, 263, 123
White R.L., Becker R.H., Helfand D.J. and Gregg M.D, 1997, ApJ, 475, 479
Windhorst R.A., van Heerde G.M. \& Katgert P., 1984,A\&AS, 58, 1
Windhorst R.A., Mathis D.F. and Neuschaefer L.W., 1990, in Kron R.G.,
ed. ASP Conf. Ser. Vol. 10, {\it Evolution of the Universe of Galaxies}
Bookcrafters, Provo, p. 389
Wunderlich E., Klein U. \& Wielebinski R., 1987, A\&AS, 69, 487