A ug 2 00 7 Discovery of Radio Jets in z ∼ 2 ULIRGs with Deep 9 . 7 μ m Silicate Absorption

Recent Spitzer observations have revealed a substantial population of z∼ 2 ULIRGs with deep silicate absorption (τ9.7> 1). This paper reports a 20cm radio study of such a sample to elucidate their physical nature. We discover that a substantial fraction (40%) of deep silicate absorption ULIRGs at z∼ 2 are moderately radio-loud with L1.4GHz=10 25 – 10WHz. This is in strong contrast with z < ∼ 1 radio galaxies and radio-loud quasars where none of the sources with available IRS spectra have τ9.7> 1. In addition, we observe radio jets in two of our sources where one has a double lobe structure ∼ 200 kpc in extent, and another shows a one-sided jet extending ∼ 90 kpc from the nucleus. The likely high inclination of the latter, coupled with its deep silicate absorption, implies the mid-IR obscuration does not share an axis with the radio jets. These sources are highly obscured quasars, observed in the transition stage after the birth of the radio source, but before feedback effects dispel the ISM and halt the black hole accretion and starburst activity. Subject headings: galaxies:active — galaxies: high-redshift — galaxies: jets — infrared: galaxies — radio continuum: galaxies