Solving the Mystery of the Lyman Alpha Blobs

Abstract

We propose IRS Long Low and MIPS 24 micron imaging of all the Ultraluminous Infrared Galaxies (ULIRGs) associated with high-redshift, Lyman alpha blobs (LABs). The physical origin of the LABs is still unknown, with the two most likely models shocks from supernova-driven winds and escaping AGN illumination. Only with mid-infrared spectroscopy can we definitively measure the PAH strengths and PAH-to-continuum ratios of these UV-bright ULIRGS, quantifying the relative contributions of AGN versus starburst. We will also be sensitive to the broad 9.7 micron silicate feature, which can be used to estimate extinction to the embedded mid-IR sources. Half of all known LAB ULIRGs lie at z=3.09, moving the majority of strong PAH features out the 24 micron filter. None of these z=3.09 LABs have been detected at 24 micron, despite SCUBA 850 micron detections, so for this half of the sample we propose deep MIPS 24 micron imaging in order to either detect the sources or provide strongly constraining upper limits on 24 micron flux. The 850/24 micron ratio measures the relative contribution of hot and cold dust emission, which places strong constraints on AGN energy contributions.