POLYCYCLIC AROMATIC HYDROCARBON EMISSION WITHIN Lyα BLOBS

We present Spitzer observations of Ly alpha blobs (LABs) at z = 2.38-3.09. The mid-infrared ratios (4.5 mu m/8 mu m and 8 mu m/24 mu m) indicate that similar to 60% of LAB infrared counterparts are cool, consistent with their infrared output being dominated by star formation and not active galactic nuclei (AGNs). The rest have a substantial hot dust component that one would expect from an AGN or an extreme starburst. Comparing the mid-infrared to submillimeter fluxes (similar to 850 mu m or rest-frame far-infrared) also indicates that a large percentage (similar to 2/3) of the LAB counterparts have total bolometric energy output dominated by star formation, although the number of sources with submillimeter detections or meaningful upper limits remains small (similar to 10). We obtained Infrared Spectrograph (IRS) spectra of six infrared-bright sources associated with LABs. Four of these sources have measurable polycyclic aromatic hydrocarbon (PAH) emission features, indicative of significant star formation, while the remaining two show a featureless continuum, indicative of infrared energy output completely dominated by an AGN. Two of the counterparts with PAHs are mixed sources, with PAH line-to-continuum ratios and PAH equivalent widths indicative of large energy contributions from both star formation and AGN. Most of the LAB infrared counterparts have large stellar masses, around 10(11)M(circle dot). There is a weak trend of mass upper limit with the Ly alpha luminosity of the host blob, particularly after the most likely AGN contaminants are removed. The range in likely energy sources for the LABs found in this and previous studies suggests that there is no single source of power that is producing all the known LABs.