2007ApJ...655L...9G

Using Spitzer Space Telescope IRAC (3.6-8 µm) and MIPS (24 µm) imaging, as well as Hubble Space Telescope optical observations, we identify the IRAC counterparts of the luminous power sources residing within the two largest and brightest Lyα-emitting nebulae (LABs) in the SA 22 protocluster at z=3.09 (LAB 1 and LAB 2). These sources are also both submillimeter galaxies (SMGs). From their rest-frame optical/near-infrared colors, we conclude that the SMG in LAB 1 is likely starburst dominated and heavily obscured (A_V∼3). In contrast, LAB 2 has excess rest-frame ∼2 µm emission (over that expected from starlight) and hosts a hard-X-ray-emitting active galactic nucleus (AGN) at the proposed location of the SMG, consistent with the presence of an AGN. We conclude that LAB 1 and LAB 2 appear to have very different energy sources despite having similar Lyα spatial extents and luminosities, although it remains unclear whether ongoing star formation or periodic AGN heating is responsible for the extended Lyα emission. We find that the mid-infrared properties of the SMGs lying in LAB 1 and LAB 2 are similar to those of the wider SMG population, and so it is possible that extended Lyα halos are a common feature of SMGs in general.