Improved Templates for Photometric Redshifts of Submm Sources

There is growing evidence that some star-forming galaxies at z>1 are characterized by high efficiencies and specific star formation rates. In the local universe, these traits are shared by ``active'' Blue Compact Dwarf galaxies (BCDs) with compact and dense star-forming regions. The Spectral Energy Distributions (SEDs) of these BCDs are dominated by young massive star clusters, embedded in a cocoon of dust. In this Letter, we incorporate these BCD SEDs as templates for two samples of high-redshift galaxy populations selected at submm wavelengths. Because of the severe absorption of the optical light, the featureless mid-infrared spectrum, and the relatively flat radio continuum, the dusty star-cluster SEDs are good approximations to most of the submm sources in our samples. In most cases, the active BCD SEDs fit the observed photometric points better than the ``standard'' templates, M 82 and Arp 220, and predict photometric redshifts significantly closer to the spectroscopic ones. Our results strongly suggest that the embedded dusty star clusters in BCD galaxies are superior to other local templates such as M 82 and Arp 220 in fitting distant submm starburst galaxies.Comment: Accepted by ApJL: 4 pages, 2 figures, 2 table

The MicroJansky Radio Galaxy Population

We use highly spectroscopically complete observations of the radio sources from the VLA 1.4 GHz survey of the HDF-N region to study the faint radio galaxy population and its evolution. We spectrally classify the sources into four spectral types: absorbers, star formers, Seyfert galaxies, and broad-line AGNs, and we analyze their properties by type. We supplement the spectroscopic redshifts with photometric redshifts measured from the rest-frame UV to MIR spectral energy distributions. Using deep X-ray observations of the field, we do not confirm the existence of an X-ray-radio correlation for star-forming galaxies. We also do not observe any correlations between 1.4 GHz flux and R magnitude or redshift. We find that the radio powers of the host galaxies rise dramatically with increasing redshift, while the optical properties of the host galaxies show at most small changes. Assuming that the locally determined FIR-radio correlation holds at high redshifts, we estimate total FIR luminosities for the radio sources. We note that the FIR luminosity estimates for any radio-loud AGNs will be overestimates. Considering only the radio sources with quasar-like bolometric luminosities, we find a maximum ratio of candidate highly-obscured AGNs to X-ray-luminous (>10^42 ergs/s) sources of about 1.9. We use source-stacking analyses to measure the X-ray surface brightnesses of various X-ray and radio populations. We find the contributions to the 4-8 keV light from our candidate highly-obscured AGNs to be very small, and hence these sources are unable to account for the light that has been suggested may be missing at these energies.Comment: 20 pages, Accepted by The Astrophysical Journal (scheduled for 1 Jan 2007), color figures 2 and 3 can be found at http://www.astro.wisc.edu/~barger/radiopaper.htm

Nuclear star formation in the quasar PG1126-041 from adaptive optics assisted spectroscopy

We present adaptive optics assisted spectroscopy of three quasars obtained with NACO at VLT. The high angular resolution achieved with the adaptive optics (~0.08"), joined to the diagnostic power of near-IR spectroscopy, allow us to investigate the properties of the innermost 100 pc of these quasars. In the quasar with the best adaptive optics correction, PG1126-041, we spatially resolve the Pa-alpha emission within the nuclear 100 pc. The comparison with higher excitation lines suggests that the narrow Pa-alpha emission is due to nuclear star formation. The inferred intensity of the nuclear star formation (13 M(sun)/yr) may account for most of the far-IR luminosity observed in this quasar.Comment: 4 pages, 4 figures. Accepted for publication in A&

Discovery of two infrared supernovae: a new window on the SN search

We report the discovery of two supernovae (SN 1999gw and SN 2001db) obtained within the framework of an infrared monitoring campaign of Luminous Infrared Galaxies, aimed at detecting obscured supernovae. SN 2001db, extinguished by Av~5.5 mag, is the first supernova discovered in the infrared which has received the spectroscopic confirmation. This result highlights the power of infrared monitoring in detecting obscured SNe and indicates that optical surveys are probably missing a significant fraction of SNe, especially in obscured systems such as starburst galaxies. The preliminary estimate of SN rate in LIRG galaxies is about an order of magnitude higher than that expected from optical surveys.Comment: 9 pages, 7 figures, accepted for publication in A&

The nature of the absorbing torus in compact Radio Galaxies

We present BeppoSAX observations of the two radio galaxies PKS 1934-63 and S5 1946+708. Strong Iron Kalpha lines are detected in both objects indicating that the two sources are absorbed by column densities higher than 10^24 cm^(-2). Combining radio continuum, HI absorption and X-ray data we can constrain the physical state and the dimensions of the absorber. We find that the putative obscuring torus is molecular and located at a distance higher than 20 pc from the center in S5 1946+70. In PKS 1934-63 no radio nucleus has been observed. If this is due to free-free absorption a radius of only a few pc is inferred. Since the Kalpha lines have been detected only at 90% confidence, we also discuss the implications if they would be not as strong as found from our data. From our results it appears that the combination of hard X-ray data and spatially resolved HI absorption measurements provides a powerful diagnostic for conditions in the absorbing ``torus''.Comment: 8 pages, 5 figures, accepted for publication in Astronomy & Astrophysic