A population of hot, dusty ultraluminous galaxies at z≈2

We report spectroscopic redshifts for 18 muJy radio galaxies at a mean redshift of z=2.2 that are faint at both submillimeter and optical wavelengths. While the radio fluxes of these galaxies could indicate far-IR luminosities comparable to high-redshift submillimeter-selected galaxies (greater than or similar to10(12) L-circle dot), none are detected in the submillimeter. We propose that this new population of galaxies represents an extension of the high-redshift submillimeter galaxy population but with hotter characteristic dust temperatures that shift the peak of their far-IR emission to shorter wavelengths, reducing the submillimeter flux below the sensitivity of current instruments. Therefore, surveys in the submillimeter waveband may miss up to half of the most luminous, dusty galaxies at zapproximate to2. Mid-infrared observations with the Spitzer Space Telescope will be a powerful tool to test this hypothesis.