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We use ultradeep 20 cm data from the Karl G. Jansky Very Large Array and 850 micron data from SCUBA-2 and the Submillimeter Array of an 124 arcmin^2 region of the Chandra Deep Field-north to analyze the high radio power (P_20cm>10^31 erg s^-1 Hz^-1) population. We find that 20 (42+/-9%) of the spectroscopically identified z>0.8 sources have consistent star formation rates (SFRs) inferred from both submillimeter and radio observations, while the remaining sources have lower (mostly undetected) submillimeter fluxes, suggesting that active galactic nucleus (AGN) activity dominates the radio power in these sources. We develop a classification scheme based on the ratio of submillimeter flux to radio power versus radio power and find that it agrees with AGN and star-forming galaxy classifications from Very Long Baseline Interferometry. Our results provide support for an extremely rapid drop in the number of high SFR galaxies above about a thousand solar masses per year (Kroupa initial mass function) and for the locally determined relation between X-ray luminosity and radio power for star-forming galaxies applying at high redshifts and high radio powers. We measure far-infrared (FIR) luminosities and find that some AGNs lie on the FIR-radio correlation, while others scatter below. The AGNs that lie on the correlation appear to do so based on their emission from the AGN torus. We measure a median radio size of 1.0+/-0.3 arcsecond for the star-forming galaxies. The radio sizes of the star-forming galaxies are generally larger than those of the AGNs., Published in ApJ. 10 pages, 8 figures

A large number of deep and wide-field radio interferometric surveys are being designed to measure accurate statistics of faint source populations. Most require mosaic observations, and expect to benefit from the sensitivity provided by broad-band instruments. In this paper, we present preliminary results from a comparison of several wideband imaging methods in the context of how accurately they reconstruct the intensities and spectral indices of micro-Jy level sources., Comment: 4 pages 1 figure

We present an X-ray stacking analysis of a sample of 38 submillimeter galaxies with =2.6 discovered at >4�� significance in the Lockman Hole North with the MAMBO array. We find a 5�� detection in the stacked soft band (0.5-2.0 keV) image, and no significant detection in the hard band (2.0-8 keV). We also perform rest-frame spectral stacking based on spectroscopic and photometric redshifts and find a ~4�� detection of Fe K�� emission with an equivalent width of EW>1 keV. The centroid of the Fe K�� emission lies near 6.7 keV, indicating a possible contribution from highly ionized Fe XXV or Fe XXVI; there is also a slight indication that the line emission is more spatially extended than the X-ray continuum. This is the first X-ray analysis of a complete, flux-limited sample of SMGs with statistically robust radio counterparts., 20 pages, 11 figures, accepted for publication in ApJ

We present new Hubble, Gemini-S, and Chandra observations of the radio galaxy 0313-192, which hosts a 350-kpc double source and jets, even though previous data have suggested that it is a spiral galaxy. We measure the bulge scale and luminosity, radial and vertical profiles of disk starlight, and consider the distributions of H II regions and absorbing dust. In each case, the HST data confirm its classification as an edge-on spiral galaxy, the only such system known to produce such an extended radio source of this kind. The Gemini near-IR images and Chandra spectral fit reveal a strongly obscured central AGN, seen through the entire ISM path length of the disk and showing X-ray evidence of additional absorption from warm or dense material close to the central object. We consider several possible mechanisms for producing such a rare combination of AGN and host properties, some combination of which may be at work. These include an unusually luminous bulge (suggesting a black hole of mass 0.5-0.9 billion solar masses), orientation of the jets near the pole of the gas-rich disk, and some evidence of a weak gravitational interaction which has warped the disk and could have enhanced fuelling of the central engine. An X-ray counterpart of the kiloparsec-scale radio jet emerges to the south; jet/counterjet limits in both radio and X-ray allow them to be symmetric if seen more than 15 degrees from the plane of the sky, still consistent with the jet axes being within ~30 degrees of the poles of the gas-rich galaxy disk. A linear or disklike emission-line structure is seen around thenucleus, inclined by ~20 degrees to the stellar disk but nearly perpendicular to the jets; this may represent the aftermath of a galaxy encounter, where gas is photoionized by the nuclear continuum., In press, Astron. J. 9 figures; 8 in shrunk JPEG form. Supported by NASA through STScI grant HST-GO-09376.01 and Chandra grant GO4-5118X

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 ApJ

We used the HST WFPC2 to obtain I-band images of the centers of 81 brightest cluster galaxies (BCGs), drawn from a volume-limited sample of nearby BCGs. The images show a rich variety of morphological features, including multiple or double nuclei, dust, stellar disks, point source nuclei, and central surface brightness depressions. High resolution surface brightness profiles could be inferred for 60 galaxies. Of those, 88% have well-resolved cores. Twelve percent of the BCG sample lacks a well-resolved core; all but one of these BCGs have ``power-law'' profiles. Some of these galaxies have higher luminosities than any power-law galaxy identified by Faber et al. (1997), and have physical upper limits on the break radius well below the values observed for core galaxies of the same luminosity. These results support the idea that the central structure of early-type galaxies is bimodal in its physical properties, but also suggest that there exist high luminosity galaxies with power-law profiles (or unusually small cores). The BCGs in the latter category tend to fall at the low end of the BCG luminosity function and tend to have low values of the quantity alpha (the logarithmic slope of the metric luminosity as a function of radius, at 10 kpc). Since theoretical calculations have shown that the luminosities and alpha values of BCGs grow with time as a result of accretion, this suggests a scenario in which elliptical galaxies evolve from power-law profiles to core profiles through accretion and merging. This is consistent with theoretical scenarios that invoke the formation of massive black hole binaries during merger events (Abridged)., Comment: Accepted for publication in AJ. Postscript file with high resolution figures (1 and 3) is available at http://spider.ipac.caltech.edu/staff/seppo/bcgfigs

(Abridged) We report on the properties of radio-selected galaxies within 30 very-rich Abell clusters with z < 0.25. These radio data sample the ultra-faint (L(1.4) > 2E22 W/Hz) radio galaxy population with M_R < -21 using the well-known FIR/radio correlation to link the radio with ongoing star formation within individual cluster galaxies. These radio-selected galaxies reveal the `active' galaxy population (starburst and active galactic nuclei) within these rich cluster environments that can be identified regardless of their level of dust obscuration. For all clusters in our sample, we are sensitive to star formation rates (M > 5 M_sun) > 5 M_sun/yr. We have found that the excess number of low-luminosity `starburst' radio-selected galaxies (SBRG) found by Owen et. al. 1999 in Abell 2125 is not indicative of other rich clusters in our sample. The average fraction of SBRG is = 0.022+/-0.003. The A2125 fraction is f(SBRG) = 0.09+/-10.03 which is significantly different from the sample average at a >99.99% confidence level. The bimodal structure of both the x-ray brightness distribution and optical adaptively smoothed images of A1278 and A2125 suggests that ongoing cluster-cluster mergers may be enhancing this SBRG population. There is a significant spatial distribution difference between the low and high-luminosity (HLRG) radio-selected populations. The HLRGs seem to be a subclass of the cluster's massive red elliptical population, while the SBRGs have a projected radial distribution more like the blue spiral population. Our results indicate that most of the SBRGs are probably gas-rich disk galaxies undergoing > 5 M_sun/yr of star-formation., 18 pages, 6 figures, accepted by AJ