Spitzer Infrared Properties of Lyman α Emitters

We present results on the infrared properties of Lyman α emitters. At z=0.3 we demonstrate that our sample of 50 GALEX-identified emitters possess the same extinction properties as similarly ultraviolet-bright galaxies at the same redshift. The AGN fraction for these z=0.3 sources is low, 10-20%, and they show no correlation between Lyα flux and total infrared luminosity. At z=2.4-3.1 we discuss a sample of Lyman α blobs. Roughly two thirds of these blobs have infrared counterparts with infrared and sub-mm colors indicating they are dominated by star formation. Of the six IRS spectra taken of blob counterparts, four show PAH features. Their equivalent widths indicate two are strongly star formation dominated, while the other two are mixed sources with a significant contribution from an AGN. 1. Escaping Lyman α Emission The discovery of Lyα emitters is now common place in the high-redshift universe. Often it is the only measurable line available and in cases of extremely high equivalent width it can be effectively the only information we possess about the galaxy. However, Lyα is a resonant ultraviolet line, both easily scattered and highly vulnerable to dust extinction. We still do not really understand the mechanism by which it escapes the galaxy, i.e., why are some galaxies Lyα emitters and others are not? It could be a function of dust extinction, orientation, or how disturbed the interstellar medium has been by either interaction or a powerful starburst. Until the Lyα escape mechanism is understood, we will not be able to account for the likely biases in the selection of these most distant high-redshift galaxies. Studies at all wavelengths, at redshifts both high and low, are needed to address this. We focus on the infrared properties of these sources, where we can find the most powerful diagnostics for dust re-emission and the presence of an AGN. 2. Lyα Emitters at z=0.3 One of the reasons little is known about the escape mechanisms of Lyα is that, up until recently, there have been only a handful of low redshift examples(i.e., Hayes et al. 2007, Keel et al. 2005). Thanks to a GALEX sample of over 100 z∼0.3 Lyα emitters (Deharveng et al. 2008, Cowie et al. 2010) this dearth of local Lyα-emitters is finally being addressed. We examine the Spitzer properties of sub-sample of 50 of