The GOODS-N Jansky VLA 10 GHz Pilot Survey: Sizes of Star-forming μJY Radio Sources

Abstract

Our sensitive ( ), high-resolution (FWHM ), 10 GHz image covering a single Karl G. Jansky Very Large Array (VLA) primary beam (FWHM ) in the GOODS-N field contains 32 sources with and optical and/or near-infrared (OIR) counterparts. Most are about as large as the star-forming regions that power them. Their median FWHM major axis is , with rms scatter . In units of the effective radius that encloses half their flux, these radio sizes are , with rms scatter . These sizes are smaller than those measured at lower radio frequencies, but agree with dust emission sizes measured at mm/sub-mm wavelengths and extinction-corrected H α sizes. We made a low-resolution ( ) image with better brightness sensitivity, in order to detect extended sources and measure matched-resolution spectral indices . It contains six new sources with and OIR counterparts. The median redshift of all 38 sources is . The 19 sources with 1.4 GHz counterparts have a median spectral index of , with rms scatter . Including upper limits on α for sources not detected at 1.4 GHz flattens the median to , suggesting that the μ Jy radio sources at higher redshifts—and hence those selected at higher rest-frame frequencies—may have flatter spectra. If the non-thermal spectral index is , the median thermal fraction of sources selected at median rest-frame frequency is ≳48%.