New Views into High Redshift Star-formation from GOODS

The GOODS-North field centered around the historical Hubble Deep Field-North provides one of the richest multiwavelength datasets compiled, spanning radio to X-ray frequencies, for studying the formation and evolution of galaxies at high redshift. In particular, the unprecedented sensitivity of the Spitzer/GOODS 24μm observations allows an unbiased measure of dust-enshrouded star-formation and AGN activity in typical L∗ galaxies rather than the extreme, hyperluminous galaxies which far-infrared surveys detect. We consider a spectroscopically selected sample of 226 galaxies at z>1.5 of which 135 are in the redshift range 1.5< z < 3. Less than 1/4 of galaxies considered here are detected at 24μm. They primarily have red UV slopes but consitute about only 20% of the red galaxies in this sample indicating that the red UV colors of the majority of objects is due to an evolved stellar population. Although 24μm sources are sparse in number, their combined energy output in the 1.5< z < 3 range exceeds the combined UV luminosity of the sample by a factor of ∼30. We also find that AGN, identified by their X-ray to infrared luminosity ratios, account for <10% of the sources considered and contribute less than 30% of the total budget in this redshift range. The infrared luminous galaxies which are increasingly being found at high-z appear to dominate the global energetics of the Universe out to z∼3 as has previously been predicted.