Radio and Millimeter Properties of z ∼ 5.7 Lyα Emitters in the COSMOS Field: Limits on Radio AGNs, Submillimeter Galaxies, and Dust Obscuration

Abstract

We present observations at 1.4 and 250 GHz of the z ∼ 5.7 Lyα emitters (LAEs) in the COSMOS field found by Murayama et al. At 1.4 GHz there are 99 LAEs in the lower noise regions of the radio field. We do not detect any individual source down to 3 σ limits of ∼30 μJy beam -1 at 1.4 GHz, nor do we detect a source in a stacking analysis, to a 2 σ limit of 2.5 μJy beam -1. At 250 GHz we do not detect any of the 10 LAEs that are located within the central regions of the COSMOS field covered by MAMBO (20′ × 20′) to a typical 2 σ limit of S 250 < 2 mJy. The radio data imply that there are no low-luminosity radio AGNs with L 1.4 > 6 × 10 24W Hz -1 in the LAE sample. The radio and millimeter observations also rule out any highly obscured, extreme starbursts in the sample, i.e., any galaxies with massive star formation rates >1500 M⊙ yr -1 in the full sample (based on the radio data), or 500 M ⊙ yr -1 for the 10% of the LAE sample that falls in the central MAMBO field. The stacking analysis implies an upper limit to the mean massive star formation rate of ∼ 100 M⊙ yr -1. © 2007. The American Astronomical Society. All rights reserved.