Radio Observations of Infrared-Luminous High-Redshift Quasi-Stellar Objects

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Abstract
We present Very Large Array observations at 1.4 and 5 GHz of a sample of 12 quasi-stellar objects (QSOs) at z = 3.99–4.46. The sources were selected as the brightest sources at 250 GHz from the recent survey of Omont and coworkers. We detect seven sources at 1.4 GHz with flux densities S1.4 ≥ 50 μJy. These centimeter wavelength observations imply that the millimeter emission is most likely thermal dust emission. The radio through optical spectral energy distributions for these sources are within the broad range defined by lower redshift, lower optical luminosity QSOs. For two sources, the radio continuum luminosities and morphologies indicate steep-spectrum, radio-loud emission from a jet-driven radio source. For the remaining 10 sources, the 1.4 GHz flux densities, or limits, are consistent with those expected for active star-forming galaxies. If the radio emission is powered by star formation in these systems, then the implied star formation rates are on the order of 103 M⊙ yr-1. We discuss the angular sizes and spatial distributions of the radio-emitting regions, and we consider briefly these results in the context of coeval black hole and stellar bulge formation in galaxies.
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