99 research outputs found
The Deep SWIRE Field III. WIYN Spectroscopy
We present the results of spectroscopy using HYDRA on the WIYN 3.5m telescope
of objects in the deep SWIRE radio field. The goal of the project was to
determine spectroscopic redshifts for as many of the brighter objects in the
field as possible, especially those detected in the radio and at 24 microns.
These redshifts are primarily being used in studies of galaxy evolution and the
connection of that evolution to AGN and star-formation. Redshifts measured for
365 individual objects are reported. The redshifts range from 0.03 to 2.5,
mostly with z < 0.9. The sources were selected to be within the WIYN HYDRA
field of approximately 30' in radius from the center of the SWIRE deep field,
10h46m00s, 59d 01'00" (J2000). Optical sources for spectroscopic observation
were selected from a r-band image of the field. A priority list of
spectroscopic targets was established in the following order: 20cm detections,
24 micron detections, galaxies with r < 20 and the balance made up of fainter
galaxies in the field. We provide a table listing the galaxy positions,
measured redshift and error, and note any emission lines that were visible in
the spectrum. In practice almost all the galaxies with r < 19 were observed
including all of the radio sources and most of the 24 microns sources with r <
20 and a sample of radio sources which had fainter optical counterparts on the
r-band image.Comment: 6 pages, 3 tables, 2 figures, full electronic tables at
http://www.aoc.nrao.edu/~fowen/papers/SWIRE/WIYNpaper3/, accepted ApJ Suppl
Serie
Current Star Formation in Post-Starburst Galaxies?
Radio continuum observations are a probe of star formation in galaxies, and
are unaffected by dust extinction. Observations of the distant rich cluster Cl
0939+4713 have detected radio galaxies classified as post-starburst (``k+a'')
on the basis of their optical spectra, and presumably this situation arises
from heavily dust-obscured star formation (Smail et al. 1999). We present the
results of a radio continuum survey of post-starburst galaxies identified from
the Las Campanas Redshift Survey by Zabludoff et al. (1996). This sample was
selected using very stringent criteria, and therefore provides an estimate on
the incidence of potential star formation in galaxies whose optical spectra
exhibit the strongest post-starburst features. We detected two of fifteen such
galaxies at radio luminosities consistent with moderate levels of star
formation. This result underscores the potential importance of dust extinction
when investigating star formation in galaxies.Comment: Replaced with corrected version of Table
A 20cm VLA Survey of Abell Clusters of Galaxies VI. Radio/Optical Luminosity Functions
From a statistically complete sample of 188 radio galaxies in Abell clusters,
we examine the radio/optical correlations, the FR I/II division, and the
univariate and bivariate luminosity functions. As suggested by Owen (1993), the
FR I/II division is shown to be a strong function of the optical luminosity of
the host galaxy (proportional to L_opt^2). This dependence is also seen in the
bivariate luminosity function, which suggests that the evolutionary tracks of
radio sources and/or the initial conditions in the source are governed by the
host galaxy properties. The probability for detecting radio emission increases
with optical luminosity. The optical dependence is clearly separated in the
integral luminosity functions which can be used as a constraint to models of FR
I radio power evolution. Additionally, the source counts from the integrated
univariate radio luminosity function (RLF) are consistent with our suggestion
in paper V that radio sources may be a transient phenomenon which occurs in all
elliptical galaxies at some time (or several times) over their lifetime. We
find no statistically significant differences in the luminosity functions
between rich cluster samples and radio sources not selected to reside in
clusters. These results suggest that all radio galaxies live in similar
environments in that the optical luminosity and the properties of the host
galaxy are the most important parameters which affect radio source formation
and evolution.Comment: 21 pages LaTeX, 3 tables, 12 figures. To appear in July 1996 A
The Radio Galaxy Populations of Nearby Northern Abell Clusters
We report on the use of the NRAO VLA Sky Survey (NVSS) to identify radio
galaxie s in eighteen nearby Abell clusters. The listings extend from the cores
of the clusters out to radii of 3 Mpc, which corresponds to 1.5 Abell radii and
approximately four orders of magnitude in galaxy density. To create a truly
useful catalog, we have collected optical spectra for nearly all of the
galaxies lacking public velocity measurements. Consequently, we are able to
discriminate between those radio galaxies seen in projection on the cluster and
those which are in actuality cluster members. The resulting catalog consists of
329 cluster radio galaxies plus 138 galaxies deemed foreground/background
objects, and new velocity measurements are reported for 273 of these radio
galaxies.
The motivation for the catalog is the study of galaxy evolution in the
cluster environment. The radio luminosity function (RLF) is a powerful tool in
the identification of active galaxies, as it is dominated by star-forming
galaxies at intermediate luminosities and active galactic nuclei (AGN) at
higher luminosities. The flux limit of the NVSS allows us to identify AGN and
star- forming galaxies down to star formation rates (SFR) less than 1 solar
mass per year. This sensitivity, coupled with the all-sky nature of the NVSS,
allows us to produce a catalog of considerable depth and breadth. In addition
to these data, we report detected infrared fluxes and upper limits obtained
from IRAS data. It is hoped that this database will prove useful in a number of
potential studies of the effect of environment on galaxy evolution.Comment: 53 pages (AASTeX v5.0), plus 3 figures. To appear in the
Astrophysical Journal Supplement Serie
VLA 1.4GHz observations of the GOODS-North Field: Data Reduction and Analysis
We describe deep, new, wide-field radio continuum observations of the Great
Observatories Origins Deep Survey -- North (GOODS-N) field. The resulting map
has a synthesized beamsize of ~1.7" and an r.m.s. noise level of ~3.9uJy/bm
near its center and ~8uJy/bm at 15', from phase center. We have cataloged 1,230
discrete radio emitters, within a 40' x 40' region, above a 5-sigma detection
threshold of ~20uJy at the field center. New techniques, pioneered by Owen &
Morrison (2008), have enabled us to achieve a dynamic range of 6800:1 in a
field that has significantly strong confusing sources. We compare the 1.4-GHz
(20-cm) source counts with those from other published radio surveys. Our
differential counts are nearly Euclidean below 100uJy with a median source
diameter of ~1.2". This adds to the evidence presented by Owen & Morrison
(2008) that the natural confusion limit may lie near ~1uJy. If the Euclidean
slope of the counts continues down to the natural confusion limit as an
extrapolation of our log N - log S, this indicates that the cutoff must be
fairly sharp below 1uJy else the cosmic microwave background temperature would
increase above 2.7K at 1.4 GHz.Comment: Accepted for publication in ApJS. 16 pages, 19 figures. Radio data
and source list can be found at http://www.ifa.hawaii.edu/~morrison/GOODSN
A Deep Radio Survey of Abell 2125 III: The Cluster Core - Merging and Stripping
We use radio, near-IR, optical, and X-ray observations to examine dynamic
processes in the central region of Abell 2125. In addition to the central
triple, including members of both major dynamical subsystems identified from a
redshift survey, this region features a galaxy showing strong evidence for
ongoing gas stripping during a high-velocity passage through the gas in the
cluster core. The disk galaxy C153 exhibits a plume stretching toward the
cluster center seen in soft X-rays by Chandra, parts of which are also seen in
[O II] emission and near-UV continuum light. HST imaging shows a distorted
disk, with star-forming knots asymmetrically distributed and remnant spiral
structure possibly defined by dust lanes. The stars and ionized gas in its disk
are kinematically decoupled, demonstrating that pressure stripping must be
important, and that tidal disruption is not the only mechanism at work.
Comparison of the gas properties seen in the X-ray and optical data on the
plume highlight significant features of the history of stripped gas in the
intracluster medium. The nucleus of C153 also hosts an AGN, shown by the weak
and distorted extended radio emission and a radio compact core. The unusual
strength of the stripping signatures in this instance is likely related to the
high relative velocity of the galaxy with respect to the intracluster medium,
during a cluster/cluster merger, and its passage very near the core of the
cluster. Another sign of recent dynamical events is diffuse starlight
asymmetrically placed about the central triple in a cD envelope. Transient and
extreme dynamical events as seen in Abell 2125 may be important drivers of
galaxy evolution in the cores of rich clusters.Comment: 36 pages, 16 figures, accepted AJ, paper with full resolution figures
is available at http:www.aoc.nrao.edu/~fowen/papers/a2125/a2125paper3.ps.g
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