No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
A very deep Westerbork survey of a field previously observed with the VLA
Abstract
The authors present a deep 21 cm radio survey of the Lynx 2 field
selected from the Leiden-Berkeley Deep Survey areas. In the main part of
the paper the authors give a review of the data reduction techniques
that were used and present a complete radio sample which they used to
determine the 1412 MHz source counts and the median angular size at the
mJy level. A comparison of this survey with a survey of the same field
with the Very Large Array is performed. A systematic position difference
as a function of distance to the field center is found. The absolute
uncertainties in the coordinate frame and flux scale are determined, as
well as the signal-to-noise dependent error distribution. Corrections
for systematic influence of the flux determining algorithm are
discussed. Finally, a search was made for variable sources in the maps.
... McGilchrist & Riley (1990), Visser et al. (1995), Lacy et al. (1995), Waldram et al. (1996), Pooley et al. (1998), Riley et al. (1999a,b); 4C Gower et al. (1967); MIYUN Zhang et al. (1997); WENSS Rengelink et al. (1997); WSRT Valentijn et al. (1977), Goss et al. (1977Goss et al. ( , 1980, Wouterloot & Dekker (1979), Habing et al. (1982), Isaacman (1981), Matthews & Spoelstra (1983), Oort & Windhorst (1985), Wieringa (1991), Roland et al. (1990), Taylor et al. (1996); WISH De Breuck et al. (2002); TXS Douglas et al. (1996); MRC Large et al. (1991); B2 Colla et al. (1970); B3 Ficarra et al. (1985); NAIC Durdin et al. (1975), Lawrence et al. (1986); SUMSS Bock et al. (1999); GB Maslowski (1972), Machalski (1978), Rys & Machalski (1987); WB92 ...
We describe the current status of CATS, a publicly accessible database (web-server http://cats.sao.ru) allowing one to search in hundreds of catalogs of astronomical objects discovered all along the electromagnetic spectrum. Our emphasis is mainly laid on catalogs of radio continuum sources observed from 30 to 15000 MHz, secondly on catalogs of objects such as radio and active stars, planetary nebulae, HII regions, supernova remnants (SNR), pulsars, nearby galaxies, AGN and quasars. CATS also includes the catalogs from the largest extragalactic surveys, like NVSS, FIRST, WENSS, VLSS, TXS, GB6, SUMSS, IRAS, 2MASS, SDSS, ROSAT, PGC, MCG, etc. In 2004 CATS comprised a total of records from over 400 catalogs in the radio, IR, optical and X-ray windows, including most of RATAN--600 catalogs. CATS is being expanded and updated, both with newly published catalogs as well as older ones which we have created in electronic form for the first time. We describe the principles of organization of the database of astrophysical catalogs and the main functions of CATS. Comment: 12 pages, 1 figure
Before analyzing the major breakthroughs of BeppoSAX, which allowed the first multi-wavelength detections of GRB afterglows, we will say a few words about the mission and its instruments. In the introduction to this chapter, it is important to mention the remarkable work done by the scientific and technical teams, which were strongly motivated by two researchers, E. Costa and F. Frontera. These two reseachers were very excited by the GRB mystery and they knew that the set of instruments on-board BeppoSAX were particularly well adapted to the hunt for GRBs and specifically to their rapid follow-up which, as we have seen, had been impossible earlier.
We have used the VLA at 8.44 GHz to measure fluctuations in the cosmic
background radiation (CBR) from two deep images, each 7 x 7 arcmin in
size. No fluctuations between the angular scales 10 and 200 arcsec were
detected. The most accurate limit (95 percent confidence) is
DeltaT/T(CBR) less than 1.9 x 10 exp -5 for 80 arcsec resolution.
Similar limits have been obtained for the circularly and linearly
polarized components of the CBR fluctuations. All analysis was made on
dirty images, in which the statistical properties of instrumental and
sky fluctuations are well-defined.
A field of area 0.000015 sr with unprecedented sensitivity was imaged in
order to compile a complete catalog of 62 microJy radio sources with a
peak flux density at 5 GHz greater than 16 microJy at 8 arsec resoluton
and a typical positional accuracy of 0.2 arcsec. An analysis of the
image intensity distribution below the detection limit indicates that
the slope of the integral count between 2 and 16 microJy is -1.3 + or -
0.2. Thus, the slope of the count between 2 and 1000 microJy is nearly
constant and close to the Euclidean value of -1.5. It is found that the
average angular size of the sources appears to increase at flux
densities below 60 microJy. Fifteen of the 16 radio sources between 60
and 800 mJy have extended emission with a median size of 4 arcsec, often
in addition to a radio core. Nearly all sources have optical
counterparts brighter than about 27.5 mag, and most weak radio sources
identified with faint blue galaxies with a median magnitude of about 23.
We report the discovery of a blue star-forming region in the eastern
lobe of the nearby classical double-lobed radio galaxy 3C 285. This
region is elongated along the radio source axis, and its optical line
emission, and possibly its optical continuum emission, appear to be
edge-brightened on the side facing the nucleus of 3C 285. We propose
that the star formation in this region was triggered by the passage of
the radio lobe through a region of dense gas in the intergalactic
medium. Our observations add support to models in which powerful radio
sources induce star formation through the compression of dense ambient
material and are also in agreement with such an interpretation for the
alignment effect observed in high-redshift radio galaxies.
The authors present the results of a deep VLA survey at 6 cm in the
Lynx.2 area of the Leiden Berkeley Deep Survey. This area was surveyed
previously with the VLA at 21 cm as reported by Windhorst et al. in
1985. The survey sensitivities are ≡15 and 28 μJy, at 6 and 21
cm, respectively. In the three 6 cm fields, chosen within the 21 cm
survey area, 58 radio sources were found. Deep optical identifications
and photometry of these sources are derived. They are based on four-band
(UJFN) Kitt peak 4 m plates. Available spectroscopic redshifts are also
listed. The authors then present and analyze the spectral index
distributions as a function of flux density and optical identification
class.
A single primary-beam area centered on α =
13h00m37s, δ = 30°34arcmin
(1950.0) near the north galactic pole was mapped with the Very Large
Array at 1.49 GHz. There are 145 sources within 22.5 arcmin of the map
center having map peak flux densities sp ≥ 70 μJy, of
which 49 were optically identified with objects brighter than
BJ ≡ 22.5 on a Palomar Schmidt IIIa-J plate. The sky
density of sources stronger than 84 μJy was determined by direct
counts of individual sources within 17 arcmin of the map center. The
authors used the confusion P(D) distribution in the central 13×13
arcmin2 of the map to estimate the density of sources between
10 and 84 μJy. The mean radio-source sky densities probed are about
103per deg2 above 87 μJy and 104per
deg2 above 10.5 μJy, comparable with the surface densities
of all galaxies brighter than J ≡ +21 and J ≡ +23.5,
respectively. An evolutionary model which fits the 1.4-GHz counts of
radio sources associated with spiral galaxies was used to predict the
sky densities and median redshifts of far-infrared (λ = 60 μ)
sources as faint as 1 mJy.
An argument is presented to the effect that the radio emission from
distant quasars and radio galaxies is not randomly directed, but rather
has preferred orientations with respect to surrounding large-scale
structures. In particular, the radio major axes of high-redshift sources
are found to exhibit a significant tendency to point in the direction of
neighboring quasars and radio galaxies for separations of up to about
45/h Mpc (comoving). This alignment phenomenon is very similar to that
seen at low redshifts between neighboring rich clusters and their
brightest member galaxies, which suggests that what is being observed
here is tentative evidence of the existence of a filamentary pattern of
superclustering at redshifts of about 1 or more. It is concluded that if
the alignment effect found here is confirmed with larger and more
homogeneous samples, then the orientations of extragalactic radio
sources may provide a very useful probe of large-scale structure at high
redshifts.
The NOAO 4 m Mayall Telescope has been used to obtain CCD images at the
positions of 13 radio sources discovered in a deep VLA survey at 6 cm.
The exposures reach V ≡ 24.5 mag, and identifications are
suggested for ten of the 13 sources. These identifications include one
bright QSO, one very faint object which may also be stellar, seven
galaxies with various morphologies, and one relatively bright galaxy
with emission lines. The results indicate that radio sources at these
low flux-density levels are a diverse mixture of objects.
The VLA has been used to search for radio emission from flare stars in the Pleiades. Two observational strategies were employed. First, about 1/2 sq deg of cluster, containing about 40 known flare stars, was mapped at 1.4 GHz at two epochs. More than 120 sources with flux densities greater than 0.3 mJy exist on the maps. Detailed analysis shows that all but two of these sources are probably extragalactic. The two sources identified as stellar are probably not Pleiades members as judged by their proper motions; rather, based on their colors and magnitudes, they seem to be foreground G stars. One is a known X-ray source. The second observational strategy, where five rapidly rotating flare stars were observed at three frequencies, yielded no detections. The 0.3 mJy flux-density limit of this survey is such that only the most intense outbursts of flare stars in the solar neighborhood could have been detected if those stars were at the distance of the Pleiades.
We present isophotal profiles of six faint field galaxies from some of the first deep images taken for the Hubble Space Telescope (HST) Medium Deep Survey (MDS). These have redshifts in the range z=0.126-0.401. The images were taken with the Wide Field Camera (WFC) in "parallel mode" and deconvolved with the Lucy method using as the point-spread function nearby stars in the image stack. The WFC deconvolutions have a dynamic range of 16-20 dB (4-5 mag) and an effective resolution ≲0″.2 (FWHM). The multiorbit HST images allow us to trace the morphology, light profiles, and color gradients of faint field galaxies down to V≃22-23 mag at sub-kpc resolution, since the redshift range covered is z=0.1-0.4. The goals of the MDS are to study the sub-kpc scale morphology, light profiles, and color gradients for a larger sample of faint field galaxies down to V≃23 mag, and to trace the fraction of early to late-type galaxies as function of cosmic time. In this paper we study the brighter MDS galaxies in the 13h+43° MDS field in detail, and investigate to what extent model fits with pure exponential disks or a1/4 bulges are justified at V≲22 mag. Four of the six field galaxies have light profiles that indicate (small) inner bulges following r1/4 laws down to 0″.2 resolution, plus a dominant surrounding exponential disk with little or no color gradients. Two occur in a group at z=0.401, two are barred spiral galaxies at z=0.179 and z=0.302, and two are rather subluminous (and edge-on) disk galaxies at z=0.126 and z=0.179. Our deep MDS images can detect galaxies down to V, I≲25-26 mag, and demonstrate the impressive potential of HST - even with its pre-refurbished optics - to resolve morphological details in galaxies at cosmologically significant distances (V≲23 mag). Since the median redshift of these galaxies is ≲0.4, the HST resolution allows us to study sub-kpc size scales at the galaxy, which cannot be done with stable images over wide fields from the best ground-based sites.
Deep images were made with 10 arcsec resolution at 8.44 GHz with microjansky sensitivity of two regions previously imaged at several lower frequencies. The differential microjansky source count fits a power-law distribution with slope 2.3 +/- 0.2. This slope is roughly constant between 1.41 and 8.44 GHz and between S(v) = about 4 and X(v) = 1000 microJy. Unless the majority of radio sources at microJy levels are local, their average luminosity and/or space density probably has evolved with cosmic epoch in order to sustain the steep and nearly Euclidean value of the slope over such a large range in flux density. The 8.44 GHz counts probably converge at less than the 1 microjansky level if the evolutionary properties of these weak sources are similar to those of luminous gE radio galaxies and quasars. The median angular size of sources detected at 8.44 GHz at microjansky levels is 2.6 +/- 1.4 arcsec, and 40 percent of the source are larger than 5 arcsec.
Observations of a single primary-beam area centered on alpha = 8h 52m
15s and delta = +17deg 16arcmin (1950.0) are presented, as performed
with an array at 1.452 GHz. A source list, resulting from an rms map
noise of 0.030 + or - 0.001 mJy, is complete to a map peak flux density
(0.2 mJy) within 25 arcmin of the field center. Source counts between
0.2 and 5 mJy were determined from this region. Data suggest that the
faintest sources have absolute radio luminosities (10 to the 24th W/Hz),
and no significant evolution is detected. Most of the radio source
background appears to be a result of sources stronger than 0.2 mJy. It
is also determined that the rms sky-temperature fluctuation in the
central 10 x 10 sq arcmin of the map is less than 0.029 K on an
approximate 19 arcsec angular scale. It is concluded that theories which
attribute the cosmic microwave background to thermalized radiation are
constrained by this limit.
A single primary-beam area centered on the ascension 08h52m15s,
declination +17 deg 16 arcmin field has been observed for 4 x 12 hr with
the Very Large Array at 1.46 GHz. The resultant map has an rms noise
level of 13.3 micro-Jy and yields a reliable list of sources with map
peak flux densities over 84 micro-Jy. The use of the Cambridge automatic
plate measuring machine to make position-coincidence optical
identifications is described. Direct source counts in the flux-density
range 84-1000 micro-Jy are obtained, and the P(D) distribution of the
central portion of the map is used to estimate the sky density of
sources as faint as 30 micro-Jy. An upper limit to the rms temperature
fluctuation in the cosmic microwave background on angular scales of
about 19 arcsec is obtained and compared with predictions from models of
star formation at early epochs.