Radio and Infrared Selected Optically Invisible Sources in the Boötes Ndwfs

We have combined data from the NOAO Deep Wide-Field Survey in Boötes and the Spitzer Space Telescope to determine basic properties for sixteen optically “invisible” MIPS 24 μm (OIMS) and thirty-five optically “invisible” radio (OIRS) sources, including their spectral energy distributions (SED) and luminosities. Most OIMSs possess steep power-law SEDs over λrest = 1 − 10 μm, indicating the presence of obscured AGN in agreement with Spitzer spectroscopy. These objects are extremely luminous at rest-frame near and mid-IR (νLν(5 μm) ≈ 10 38 − 10 W), consistent with accretion near the Eddington limit and further implying that they host buried QSOs. The majority of the IRAC detected OIRSs have flat 3.6 to 24 μm SEDs, implying comparable emission from stellar photospheres and hot AGN illuminated dust. This may reflect relatively small amounts of dust close to the central engine or current low mass accretion rates. A small subset of OIRSs appear to be starburst dominated with photometric redshifts from 1.0 to 4.5. The OIMSs and OIRSs with significant starburst components have similar LK and stellar masses (M∗ ≈ 10 11 M⊙) assuming minimal AGN contribution. Roughly half of the OIRSs are not detected by Spitzer’s IRAC or MIPS. These are most likely z & 2 radio galaxies. The IRAC detected OIRSs are more likely than OIMSs to appear non point-like in the 3.6 μm and 4.5 μm images, suggesting that interactions play a role in triggering their activity. The AGN powered OIMSs may represent sub-millimeter galaxies making the transition from starburst to accretion dominance in their evolution to current epoch massive ellipticals. Subject headings: galaxies: high-redshift – galaxies: starburst – galaxies: active – infrared: galaxies – radio continuum: galaxies