Frazer N. Owen

SWIRE: The SIRTF Wide-Area Infrared Extragalactic Survey

The largest of the SIRTF Legacy programs, SWIRE will survey 65 sq. deg. in seven high latitude fields selected to be the best wide low-extinction windows into the extragalactic sky. SWIRE will detect millions of spheroids, disks and starburst galaxies to z>3 and will map L* and brighter systems on scales up to 150 Mpc at z∼0.5–1. It will also detect ∼104 low extinction AGN and large numbers of obscured AGN. An extensive program of complementary observations is underway. The data are non-proprietary and will be made available beginning in Spring 2004.

20 CM 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.

High-resolution, high dynamic range VLA images of the M87 jet at 2 centimeters

New high-dynamic-range radio observations, made with the VLA in the A array at 2 cm with a resolution of 0.1 arcsec, are reported. The new maps show a complex pattern of filamentary and other fine-scale structures in the jet. A new physical interpretation of the jet, suggested by these observations, is presented. It is concluded that the overall morphology of M87 is more consistent with a boundary layer phenomena rather than with a structure dominated by shocks or other centrally driven flow phenomena. This morphology appears to be most consistent with a picture in which electrodynamic phenomena play an important role in the physics. 27 refs.

Faraday rotation in cooling flow clusters of galaxies. I - Radio and X-ray observations of Abell 1795

We present new, multiwavelength Very Large Array observations of the radio galaxy 1346+268 in the center of cooling flow cluster Abell 1795. With the high resolution (0.6) observations, the radio source is generally 10% to 30% polarized. We find large Faraday rotation measures, exceeding 3000 rad m −2 in places. Using the x-ray images of Abell 1795 from the Einstein database, we have modeled the distribution of the hot, x-ray emitting gas. The large rotation measures could be induced by the magneto-ionized intracluster medium. The field must be typically > 20 μG near the cluster center. It the field is not ordered, it may have a similar energy density as the thermal energy density in the x-ray emitting gas

Clumped X-ray emission around radio galaxies in Abell clusters

We have made a comparison of the X-ray and radio morphologies for a sample of 41 rich cluster fields using Einstein Observatory Imaging Proportional Counter (IPC) and Very Large Array (VLA) 20 cm images. Surprisingly, we find that 75% of the radio galaxies have a statistically significant X-ray peak or subclump within 5 min of the radio galaxy position. The X-ray luminosity and the generally extended nature of the X-ray subclumps suggest that these subclumps are overdense regions emitting free-free radiation, although there is also evidence for Active Galactic Nuclei (AGN) X-ray emission coming from some of the more compact, high surface brightness X-ray peaks. Some interesting correlations with radio morphology were also discovered. For clusters which contain wide-angle-tailed radio sources associated with centrally dominant galaxies, there are significant elongations or clumps in the central X-ray emission which are unusual for this type of cluster. We suggest that cluster radio galaxies are pointers to particular clusters or regions within clusters that have recently undergone mergers between cluster subsystems.

Radio Sources with Wide-Angle Tails in Abell Clusters of Galaxies

Observations are presented of six previously unreported radio sources in rich clusters of galaxies. These sources were discovered during a survey of radio sources in Abell clusters of galaxies, using the NRAO interferometer. Total intensity maps at 2695 MHz and optical identifications are reported. Physical parameters are also derived for these radio galaxies, and their optical properties are summarized. It is argued that the sources presented here are a simple extension of the head-tail class of radio sources, only with larger angles between their twin tails. Sources with widely diverging tails usually seem to be associated with one of the more dominant galaxies in a rich cluster, unlike radio galaxies with long, thin tails. These wide-tail sources are also ususally of higher radio luminosity than those with narrower tails. Some possible explanations of these correlations are discussed. (AIP)

ABELL 2255: INCREASED STAR FORMATION AND AGN ACTIVITY IN A CLUSTER-CLUSTER MERGER

Deep VLA 1.4 GHz radio continuum imaging of Abell 2255 is presented. This cluster is among the better nearby candidates for rich cluster-cluster merger systems, with evidence including an elongated X-ray morphology, the presence of a radio halo, and substructure present in its galaxy distribution. Our radio observations reach an rms sensitivity of ~40 μJy beam-1, enabling us to detect (at 5 σ) star formation rates as low as 1.4 M⊙ yr-1 from the center of the cluster out to a radial distance of 3 h Mpc. The radio data are complemented by optical imaging and a large spectroscopic database, allowing us to separate all galaxies with M ≤ -20 into cluster members and foreground/background galaxies. The spectra are also used to associate the galaxies radio emission with either star formation or active galactic nuclei (AGNs). We compare the resulting cluster radio galaxy population with those of 19 other nearby Abell clusters and find strong evidence for an increase in the frequency of radio galaxies in Abell 2255. This increase is seen in two separate types of galaxies: powerful radio AGNs and optically faint star-forming galaxies. The optical spectra of the latter often indicate current or recent starbursts, and these galaxies appear to be distributed along an axis perpendicular to the probable merger axis. We assess these factors in light of models of galaxy evolution and suggest that the cluster-cluster merger is responsible for triggering galaxy activity in Abell 2255.

Flow dynamics and bending of wide-angle tailed radio sources

The dynamics of tailed radio sources (WATs) is studied on the basis of VLA observations of 11 wide-angle WATs at 6 and 20 cm. These new images, in conjunction with optical and X-ray data, are used to describe the unifying characteristics of this class. WATs are found in centers of clusters without cooling cores, associated with galaxies of low space velocity. They are large sources, extending at least 50 kpc from the cluster center, and they have radio power close to the Fanaroff-Riley I/II break. The surface brightness and spectral distributions are used to model the flow fields and bending dynamics of the sources. Two limiting models are employed: the adiabatic model, in which no in situ energization takes place, and the kinetic model, in which all of the radio luminosity comes from in situ energization. It is found that the sources cannot be bent by the slow galaxy motion in the kinetic model. The sources can be bent by the ram pressure of a slowly moving central galaxy in the adiabatic model.

The Cluster of Galaxies Surrounding Cygnus A

We report optical imaging and spectroscopy of 41 galaxies in a 22 square region surrounding Cygnus A. The results show that there is an extensive rich cluster associated with Cyg A of Abell richness of at least 1 and possibly as high as 4. The velocity histogram has two peaks, one centered on Cyg A and a more significant peak redshifted by about 2060 km s-1 from the velocity of Cyg A. The dynamical centroid of the spatial distribution is also shifted somewhat to the northwest. However, statistical tests show only weak evidence that there are two distinct clusters. The entire system has a velocity dispersion of 1581 km s-1, which is slightly larger than other, well-studied examples of rich clusters.

SCUBA observations of the sources detected in the MAMBO 1200-μm survey

We have observed 23 sources from the MAMBO 1200μm survey with SCUBA at 850μm, detecting 19 of the sources. The sources generally have low values for the ratio of 850μm to 1200μm flux. Two possible explanations for the low values are either that the sources are at very high redshifts or that the global properties of the dust in the MAMBO sources are different from the global properties of dust in low-redshift galaxies. If the former explanation is correct, we estimate that 15 of the MAMBO sources lie at z > 3.