We report on sensitive radio observations made with the VLA at 8.5 GHz centered on the Hubble Deep Field (HDF). We collected data in the A, CnB, C, DnC, and D configurations corresponding to angular ...resolutions ranging from 3 to 10 arcsec. We detected 29 radio sources in a complete sample within 46 of the HDF center and above a flux density limit of 9.0 micro-Jy. Seven of these sources are located within the HDF itself, while the remaining 22 sources are covered by the Hubble flanking fields or ground-based optical images. All of the sources in the HDF are identified with galaxies with a mean magnitude R = 21.7, while the mean magnitude of the identifications outside the HDF is R = 22.1. One radio source in the HDF, which is just below our formal completeness level but is confirmed by independent 1.4 GHz observations, has no optical counterpart above the HDF limit of R = 29. Three radio sources outside the HDF have no optical counterparts to R = 27. Based on a radio and optical positional coincidence, we detected an additional 19 radio sources in this field with S(v) not less than 6.3 micro-Jy and less than 9.0 micro-Jy and R = 25 or less but which are not included in the complete sample. The microjansky radio sources are distributed over a wide range of redshifts and have a typical monochromatic luminosity of about 10 exp 23 W/Hz. The majority of the optical identifications are with luminous galaxies at modest redshifts, many with evidence for recent star formation. (Author)
We present the optical and infrared identifications of the 266 radio sources detected at 20 cm with the Very Large Array in the Chandra Deep Field-South. Using deep i-band Advanced Camera for ...Surveys, R-band Wide Field Imager, K-band SOFI NTT, K-band ISAAC VLT and Spitzer imaging data, we are able to find reliable counterparts for 254 (image95%) VLA sources. Twelve radio sources remain unidentified, and three of them are 'empty fields.' Using literature and our own data we are able to assign redshifts to 186 (image70%) radio sources: 108 are spectroscopic redshifts and 78 are reliable photometric redshifts. Based on the rest-frame colors and morphological distributions of the host galaxies, we find evidences for a change in the submillijansky radio source population: (1) above sim0.08 mJy early-type galaxies are dominating and (2) at flux densities below sim0.08 mJy, starburst galaxies become dominant.
We present full polarization Very Long Baseline Array (VLBA) observations at 5 and 15 GHz of 24 compact active galactic nuclei (AGNs). These sources were observed as part of a pilot project to ...demonstrate the feasibility of conducting a large VLBI survey to further our understanding of the physical properties and temporal evolution of AGN jets. The sample is drawn from the Cosmic Lens All-Sky Survey (CLASS) where it overlaps with the Sloan Digital Sky Survey at declinations north of 15 degree . There are 2100 CLASS sources brighter than 50 mJy at 8.4 GHz, of which we have chosen 24 for this pilot study. All 24 sources were detected and imaged at 5 GHz with a typical dynamic range of 500: 1, and 21 of 24 sources were detected and imaged at 15 GHz. Linear polarization was detected in eight sources at both 5 and 15 GHz, allowing for the creation of Faraday rotation measure (RM) images. The core RMs for the sample were found to have an average absolute value of 390 plus or minus 100 rad m super(-2). We also present the discovery of a new compact symmetric object, J08553+5751. All data were processed automatically using pipelines created or adapted for the survey.
The VLBI Space Observatory Programme (VSOP) mission is a Japanese-led project to study radio sources with submilliarcsecond angular resolution, using an orbiting 8 m telescope on board the satellite ...HALCA with a global Earth-based array of telescopes. A major program is the 5 GHz VSOP Survey Program, which we supplement here with Very Long Baseline Array observations to produce a complete and flux density-limited sample. Using statistical methods of analysis of the observed visibility amplitude versus projected (u, v) spacing, we have determined the angular size and brightness temperature distribution of bright radio emission from active galactic nuclei. On average, the cores have a diameter (full width, half-power) of 0.20 mas, which contains about 20% of the total source emission, and 14% plus or minus 6% of the cores are less than 0.04 mas in size. About 20% plus or minus 5% of the radio cores have a source frame brightness temperature T sub(b) > 1.0 x 10 super(13) K, and 3% plus or minus 2% have T sub(b) > 1.0 x 10 super(14) K. A model of the high brightness temperature tail suggests that the radio cores have brightness temperatures approximately 1 x 10 super(12) K and are beamed toward the observer with an average bulk motion of beta = 0.993 plus or minus 0.004.
We present Atacama Large Millimeter/submillimeter Array (ALMA) 860 mu m imaging of four high-redshift (z = 2.8-5.7) dusty sources that were detected using the South Pole Telescope (SPT) at 1.4 mm and ...are not seen in existing radio to far-infrared catalogs. At 1".5 resolution, the ALMA data reveal multiple images of each submillimeter source, separated by l"-3", consistent with strong lensing by intervening galaxies visible in near-IR imaging of these sources. We describe a gravitational lens modeling procedure that operates on the measured visibilities and incorporates self-calibration-like antenna phase corrections as part of the model optimization, which we use to interpret the source structure. Lens models indicate that SPT0346-52, located at z = 5.7, is one of the most luminous and intensely star-forming sources in the universe with a lensing corrected FIR luminosity of 3.7 x 10 super(13) L sub(middot in circle) and star formation surface density of 4200 M sub(middot in circle) yr super(-1) kpc super(-2). We find magnification factors of 5 to 22, with lens Einstein radii of 1".1-2".0 and Einstein enclosed masses of 1.6-7.2 x 10 super(11) M sub(middot in circle). These observations confirm the lensing origin of these objects, allow us to measure their intrinsic sizes and luminosities, and demonstrate the important role that ALMA will play in the interpretation of lensed submillimeter sources.
ABSTRACT We present Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum images of the asteroid 3 Juno obtained with an angular resolution of (60 km at 1.97 AU). The data were ...obtained over a single 4.4 hr interval, which covers 60% of the 7.2 hr rotation period, approximately centered on local transit. A sequence of 10 consecutive images reveals continuous changes in the asteroid's profile and apparent shape, in good agreement with the sky projection of the three-dimensional model of the Database of Asteroid Models from Inversion Techniques. We measure a geometric mean diameter of 259 4 km, in good agreement with past estimates from a variety of techniques and wavelengths. Due to the viewing angle and inclination of the rotational pole, the southern hemisphere dominates all of the images. The median peak brightness temperature is 215 13 K, while the median over the whole surface is 197 15 K. With the unprecedented resolution of ALMA, we find that the brightness temperature varies across the surface with higher values correlated to the subsolar point and afternoon areas and lower values beyond the evening terminator. The dominance of the subsolar point is accentuated in the final four images, suggesting a reduction in the thermal inertia of the regolith at the corresponding longitudes, which are possibly correlated to the location of the putative large impact crater. These results demonstrate ALMA's potential to resolve thermal emission from the surface of main belt asteroids and to measure accurately their position, geometric shape, rotational period, and soil characteristics.
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