Spitzer IRS Spectroscopy of Lyman Alpha Blobs

Abstract

We present Spitzer IRS Long Low and MIPS 24 micron imaging of all the Ultraluminous Infrared Galaxies (ULIRGs) associated with high-redshift, Lyman alpha blobs (LABs). LABs are an extremely energetic class of objects, so far found only in high-redshift, overdense regions. While similar in extent ( 100 kpc) and Lyman alpha flux ( 1044 ergs/s) to high-redshift radio galaxies, blobs are radio quiet and are therefore unlikely to arise from interaction with jets. The physical origin of the LABs is still unknown, with the two most likely models shocks from supernova-driven winds and escaping AGN illumination. With mid-infrared spectroscopy one can detect PAH features if they exist in these UV-bright ULIRGS, allowing a measurement of the relative contribution of AGN versus starburst. Half of all known LAB ULIRGs lie at z=3.09, where the majority of strong PAH features would actually lie outside the 24 micron filter. For this half of the sample we present 850/24 micron ratio, which roughly measures the relative contribution of hot and cold dust emission, placing strong constraints on AGN energy contributions. Show more