28 research outputs found
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 Dynamics of Abell 2125
We present 371 galaxy velocities in the field of the very rich cluster Abell
2125 (z~0.25). These were determined using optical spectroscopy collected over
several years from both the WIYN 3.5m telescope and NOAO Mayall 4m telescope.
Prior studies at a variety of wavelengths (radio, optical, and X-ray) have
indicated that A2125 is a likely cluster-cluster merger, a scenario which we
are able to test using our large velocity database. We identified 224 cluster
galaxies, which were subjected to a broad range of statistical tests using both
positional and velocity information to evaluate the cluster dynamics and
substructure. The tests confirmed the presence of substructures within the
Abell 2125 system at high significance, demonstrating that A2125 is a complex
dynamical system. Comparison of the test results with existing simulations
strengthens the merger hypothesis, and provides clues about the merger geometry
and stage. The merger model for the system can reconcile A2125's low X-ray
temperature and luminosity with its apparently high richness, and might also
explain A2125's high fraction of active galaxies identified in prior radio and
optical studies.Comment: 34 pages, including tables and 3 color figures; to appear in Ap
A catalog of Nearby Poor Clusters of Galaxies
A catalog of 732 optically selected, nearby poor clusters of galaxies
covering the entire sky north of declination is presented. The
poor clusters, called WBL clusters, were identified as concentrations of 3 or
more galaxies with photographic magnitudes brighter than 15.7, possessing a
galaxy surface overdensity of . These criteria are consistent with
those used in the identification of the original Yerkes poor clusters, and this
new catalog substantially increases the sample size of such objects. These poor
clusters cover the entire range of galaxy associations up to and including
Abell clusters, systematically including poor and rich galaxy systems spanning
over three orders of magnitude in the cluster mass function. As a result, this
new catalog contains a greater diversity of richness and structures than other
group catalogs, such as the Hickson or Yerkes catalogs. The information on
individual galaxies includes redshifts and cross-references to other galaxy
catalogs. The entries for the clusters include redshift (where available) and
cross-references to other group and cluster catalogs.Comment: 27 pages, 7 figures, + one 20-page landscape table, accepted for
publication in A
Substructure in clusters containing wide-angle tailed radio galaxies. I. New redshifts
We present new redshifts and positions for 635 galaxies in nine rich clusters
containing Wide-Angle Tailed (WAT) radio galaxies. Combined with existing data,
we now have a sample of 18 WAT-containing clusters with more than 10 redshifts.
This sample contains a substantial portion of the WAT clusters in the VLA 20 cm
survey of Abell clusters, including 75% of WAT clusters in the complete survey
(z0.09. It is a representative sample
which should not contain biases other than selection by radio morphology. We
graphically present the new data using histograms and sky maps. A
semi-automated procedure is used to search for emission lines in the spectra in
order to add and verify galaxy redshifts. We find that the average apparent
fraction of emission line galaxies is about 9% in both the clusters and the
field. We investigate the magnitude completeness of our redshift surveys with
CCD data for a test case, Abell 690. This case indicates that our galaxy target
lists are deeper than the detection limit of a typical MX exposure, and they
are 82% complete down to R=19.0. The importance of the uniformity of the
placement of fibers on targets is posited, and we evaluate this in our
datasets. We find some cases of non-uniformities which may influence dynamical
analyses. A second paper will use this database to look for correlations
between the WAT radio morphology and the cluster's dynamical state.Comment: 15 pages, 5 figures, 7 tables. To appear in the Astronomical Journa
Redshifts and Optical Properties for a Statistically Complete Sample of Poor Galaxy Clusters
From the poor cluster catalog of White et al. (1996), we define a sample of
71 optically-selected poor galaxy clusters. The surface-density enhance- ment
we require for our clusters falls between that of the loose associations of
Turner and Gott (1976) and the Hickson compact groups (Hickson, 1982). We
review the selection biases and determine the statistical comleteness of the
sample. For this sample, we report new velocity measurements made with the ARC
3.5-m Dual-Imaging spectrograph and the 2.3-m Steward Observatory MX fiber
spectrograph. Combining our own measurements with those from the literature, we
examine the velocity distributions, velocity dispersions, and 1-d velocity
substructure for our poor cluster sample, and compare our results to other poor
cluster samples. We find that approximately half of the sample may have
significant 1-d velocity substructure. The optical morphology, large-scale
environment, and velocity field of many of these clusters is indicative of
young, dynamically evolving systems. In future papers, we will use this sample
to derive the poor cluster X-ray luminosity function and gas mass function (see
astro-ph/9606120), and will examine the optical/X-ray properties of the
clusters in more detail.Comment: 15 pages LaTeX, 3 tables, 5 postscript figures. To appear in the
August 1996 Astronomical Journa
The X-ray Luminosity Function of Nearby Rich and Poor Clusters of Galaxies: A Cosmological Probe
In this letter, we present a new determination of the local (z<0.09) X-ray
luminosity function (XLF) using a large, statistical sample of 294 Abell
clusters and the ROSAT All-Sky-Survey. Given our large sample size, we have
reduced errors by a factor of two for L(X)(0.5-2keV)>10^43 ergs/sec. We combine
our data with previous work in order to explore possible constraints imposed by
the shape of the XLF on cosmological models. A set of currently viable
cosmologies is used to construct theoretical XLFs assuming Lx is proportional
to M^p and a sigma_8-Omega_0 constraint (from Viana & Liddle 1996) based on the
local X-ray temperature function. We fit these models to our observed XLF and
verify that the simplest adiabatic, analytic scaling relation (e.g. Kaiser
1986) disagrees strongly with observations. If we assume that clusters can be
described by the pre-heated, constant core-entropy models of Evrard & Henry
(1991) then the observed XLF is consistent only with 0.1 < Omega_0 < 0.4 if the
energy per unit mass in galaxies is roughly equal to the gas energy (ie if
beta=1). (abridged)Comment: 4 pages, 2 figures, accepted for publication in ApJ Letters. uses
emulateapj.st
The Cluster of Galaxies Surrounding Cygnus A
We report optical imaging and spectroscopy of 41 galaxies in a 22 arcmin
square region surrounding Cygnus A. The results show that there is an extensive
rich cluster associated with Cygnus A of Abell richness at least 1 and possibly
as high as 4. The velocity histogram has two peaks, one centered on Cygnus A,
and a more significant peak redshifted by about 2060 km/s from the velocity of
Cygnus A. The dynamical centroid of the spatial distribution is also shifted
somewhat to the NW. However, statistical tests show only weak evidence that
there are two distinct clusters. The entire system has a velocity dispersion of
1581 km/s which is slightly larger than other, well studied, examples of rich
clusters.Comment: 11 pages LaTeX, 1 table, 3 postscript figures. Accepted for
publication in Ap.J. Letter
Constraints on UV Absorption in the Intracluster Medium of Abell 1030
We present results from an extensive HST spectroscopic search for UV
absorption lines in the spectrum of the quasar B2~1028+313, which is associated
with the central dominant galaxy in the cluster Abell~1030 (). This is
one of the brightest known UV continuum sources located in a cluster, and
therefore provides an ideal opportunity to obtain stringent constraints on the
column densities of any cool absorbing gas that may be associated with the
intracluster medium (ICM). Our HST spectra were obtained with the FOS and GHRS,
and provide continuous coverage at rest-frame wavelengths from to
4060~\AA, thereby allowing the investigation of many different elements and
ionization levels. We utilize a new technique that involves simultaneous
fitting of large numbers of different transitions for each species, thereby
yielding more robust constraints on column densities than can be obtained from
a single transition. This method yields upper limits of cm on the column densities of a wide range of molecular, atomic
and ionized species that may be associated with the ICM. We also discuss a
possible \Lya and C IV absorption system associated with the quasar. We discuss
the implications of the upper limits on cool intracluster gas in the context of
the physical properties of the ICM and its relationship to the quasar.Comment: Astrophysical Journal, in press, 19 pages, includes 5 PostScript
figures. Latex format, uses aas2pp4.sty and epsfig.sty file
The X-ray Properties of Nearby Abell Clusters from the ROSAT All-Sky Survey: The Sample and Correlations with Optical Properties
We present an analysis of the X-ray emission for a complete sample of 288
Abell clusters spanning the redshift range 0.016<= z <= 0.09 from the ROSAT
All-Sky Survey. This sample is based on our 20cm VLA survey of nearby Abell
clusters. We find an X-ray detection rate of 83%. We report cluster X-ray
fluxes and luminosities and two different flux ratios indicative of the
concentration and extent of the emission. We examine correlations between the
X-ray luminosity, Abell Richness, and Bautz-Morgan and Rood-Sastry cluster
morphologies. We find a strong correlation between Lx and cluster richness
coupled to a dependence on the optical morphological type. These results are
consistent with the observed scatter between X-ray luminosity and temperature
and a large fraction of cooling flows. For each cluster field we also report
the positions, peak X-ray fluxes, and flux-ratios of all X-ray peaks above
3-sigma significance within a box of 2x2 Mpc centered on Abell's position.Comment: 59 pages including 3 tables, + 10 figures. To appear in AJ, Dec 200