We used the Karl G. Jansky Very Large Array (VLA) to image one primary beam area at 3 GHz with 8 FWHM resolution and 1.0 µJy beam −1 rms noise near the pointing center. The P (D) distribution from the central 10 arcmin of this confusion-limited image constrains the count of discrete sources in the 1 < S(µJy) < 10 range. At this level the brightness-weighted differential count S 2 n(S) is converging rapidly, as predicted by evolutionary models in which the faintest radio sources are starforming galaxies; and ≈ 96% of the background originating in galaxies has been resolved into discrete sources. About 63% of the radio background is produced by AGNs, and the remaining 37% comes from star-forming galaxies that obey the far-infrared (FIR) / radio correlation and account for most of the FIR background at λ ≈ 160 µm. Our new data confirm that radio sources powered by AGNs and star formation evolve at about the same rate, a result consistent with AGN feedback and the rough The confusion at centimeter wavelengths is low enough that neither the planned SKA nor its pathfinder ASKAP EMU survey should be confusion limited, and the ultimate source detection limit imposed by "natural" confusion is ≤ 0.01 µJy at ν = 1.4 GHz. If discrete sources dominate the bright extragalactic background reported by ARCADE 2 at 3.3 GHz, they cannot be located in or near galaxies and most are ≤ 0.03 µJy at 1.4 GHz.

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We present the evolutionary properties and luminosity functions of the radio sources belonging to the Chandra Deep Field South VLA survey, which reaches a flux density limit at 1.4 GHz of 43 µJy at the field center and redshift ∼ 5, and which includes the first radio-selected complete sample of radio-quiet active galactic nuclei (AGN). We use a new, comprehensive classification scheme based on radio, farand near-IR, optical, and X-ray data to disentangle star-forming galaxies from AGN and radio-quiet from radio-loud AGN. We confirm our previous result that star-forming galaxies become dominant only below 0.1 mJy. The sub-millijansky radio sky turns out to be a complex mix of star-forming galaxies and radio-quiet AGN evolving at a similar, strong rate; non-evolving low-luminosity radio galaxies; and declining radio powerful (P 3 × 10 24 W Hz −1 ) AGN. Our results suggest that radio emission from radio-quiet AGN is closely related to star formation. The detection of compact, high brightness temperature cores in several nearby radio-quiet AGN can be explained by the co-existence of two components, one non-evolving and AGN-related and one evolving and star-formation-related. Radio-quiet AGN are an important class of sub-millijansky sources, accounting for ∼ 30% of the sample and ∼ 60% of all AGN, and outnumbering radio-loud AGN at 0.1 mJy. This implies that future, large area sub-millijansky surveys, given the appropriate ancillary multi-wavelength data, have the potential of being able to assemble vast samples of radio-quiet AGN by-passing the problems of obscuration, which plague the optical and soft X-ray bands.

We present images of extended Hα clouds associated with 14 member galaxies in the Coma cluster obtained from deep narrow band imaging observations with the Suprime-Cam at the Subaru Telescope. The parent galaxies of the extended Hα clouds are distributed farther than 0.2 Mpc from the peak of X-ray emission of the cluster. Most of the galaxies are bluer than g −r ≈ 0.5 and they account for 57% of the blue (g −r < 0.5) bright (r < 17.8 mag) galaxies in the central region of the Coma cluster. They reside near the red-and blue-shifted edges of the radial velocity distribution of Coma cluster member galaxies. Our findings suggest that the most of the parent galaxies were recently captured by the Coma cluster potential and are now infalling toward the cluster center with their disk gas being stripped off and producing the observed Hα clouds.

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. ABSTRACTWe present ;0 4 resolution extinction-independent distributions of star formation and dust in 11 star-forming galaxies (SFGs) at z=1.3-3.0. These galaxies are selected from sensitive blank-field surveys of the 2′×2′ Hubble Ultra-Deep Field at λ=5 cm and 1.3 mm using the Karl G. Jansky Very Large Array and Atacama Large Millimeter/submillimeter Array. They have star formation rates (SFRs), stellar masses, and dust properties representative of massive main-sequence SFGs at z∼2. Morphological classification performed on spatially resolved stellar mass maps indicates a mixture of disk and morphologically disturbed systems; half of the sample harbor X-ray active galactic nuclei (AGNs), thereby representing a diversity of z∼2 SFGs undergoing vigorous mass assembly. We find that their intense star formation most frequently occurs at the location of stellar-mass concentration and extends over an area comparable to their stellar-mass distribution, with a median diameter of 4.2±1.8 kpc. This provides direct evidence of galaxy-wide star formation in distant blank-field-selected mainsequence SFGs. The typical galactic-average SFR surface density is 2.5 M e yr −1 kpc −2 , sufficiently high to drive outflows. In X-ray-selected AGN where radio emission is enhanced over the level associated with star formation, the radio excess pinpoints the AGNs, which are found to be cospatial with star formation. The median extinctionindependent size of main-sequence SFGs is two times larger than those of bright submillimeter galaxies, whose SFRs are 3-8 times larger, providing a constraint on the characteristic SFR (∼300 M e yr −1 ) above which a significant population of more compact SFGs appears to emerge.