The Angular Size Distribution of μJy Radio Sources

We made two new sensitive (rms noise sigma n approximate to 1 mu Jy beam(-1)) high-resolution (theta = 3 ''.0 and theta = 0 ''.66 FWHM) S-band (2 < nu < 4 GHz) images covering a single JVLA primary beam (FWHM approximate to 14') centered on J2000 alpha = 10(h) 46(m), delta = +59 degrees 01'. in the Lockman Hole. These images yielded a catalog of 792 radio sources, 97.7 +/- 0.8% of which have infrared counterparts stronger than S approximate to 2 mu Jy at lambda = 4.5 mu m. About 91% of the radio sources found in our previously published, comparably sensitive low-resolution (0 - 8 '' FWHM) image covering the same area were also detected at 0 ''.66 resolution, so most radio sources with S(3 GHz) greater than or similar to 5 mu Jy have angular structure phi less than or similar to 0 ''.66. The ratios of peak brightness in the 0 ''.66 and 3 '' images have a distribution indicating that most mu Jy radio sources are quite compact, with a median Gaussian angular diameter <phi > = 0 ''.3 +/- 0 ''.1 FWHM and an rms scatter sigma(phi) less than or similar to 0 ''.3 of individual sizes. Most of our mu Jy radio sources obey the tight far-infrared/radio correlation, indicating that they are powered by star formation. The median effective angular radius enclosing half the light emitted by an exponential disk is <rho(e)> approximate to <phi >/2.43 approximate to 0 ''.12, so the median effective radius of star-forming galaxies at redshifts z similar to 1 is < r(e)> approximate to 1.0 kpc.