We estimate the relative contributions of the supermassive black hole (SMBH) accretion disk, corona, and obscuring torus to the bolometric luminosity of Seyfert galaxies, using Spizter mid-infrared (MIR) observations of a complete sample of 68 nearby
active galactic nuclei from the INTEGRAL all-sky hard X-ray (HX) survey. This is the first HX-selected (above 15 keV) sample of AGNs with complementary high angular resolution, high signal to noise, MIR data. Correcting for the host galaxy contribution, we find a correlation between HX and MIR luminosities: L_MIR L_HX^(0.74+/-0.06). Assuming that the observed MIR emission is radiation from an accretion disk reprocessed in a surrounding dusty torus that subtends a solid angle decreasing with increasing luminosity (as inferred from the declining fraction of obscured AGNs), the intrinsic disk luminosity, L_D, is approximately proportional to the luminosity of the corona in the 2-300 keV energy band, L_C, with the L_D/L_C ratio varying by a factor of 2.1 around a mean value of 1.6. This ratio is a factor of ~2 smaller than for typical quasars producing the cosmic X-ray background (CXB). Therefore, over three orders of magnitude in luminosity, HX radiation carries a large, and roughly comparable, fraction of the bolometric output of AGNs. We estimate the cumulative bolometric luminosity density of local AGNs at ~(1-3)x10^40 erg/s/Mpc^3. Finally, the Compton temperature ranges between kT_c~2 and ~6 keV for nearby AGNs, compared to kT_c~2 keV for typical quasars, confirming that radiative heating of interstellar gas can play an important role in regulating SMBH growth.
This paper analyzes a sample of 489 Spitzer/IRAC sources in the Extended Groth Strip whose spectral energy distributions fit a red power law from 3.6 to 8.0 micron. The median for sources with known redshift is <z>=1.6. Though all or nearly all of th
e sample are likely to be active galactic nuclei, only 33% were detected in the EGS X-ray survey (AEGIS-X) using 200 ks Chandra observations. The detected sources are X-ray luminous with L_X > 10^43 erg/s and moderately to heavily obscured with N_H > 10^22 cm^-2. Stacking the X-ray-undetected sample members yields a statistically significant X-ray signal, suggesting that they are on average more distant or more obscured than sources with X-ray detections. The ratio of X-ray to mid-infrared fluxes suggests that a substantial fraction of the sources undetected in X-rays are obscured at the Compton-thick level, in contrast to the X-ray-detected sources, all of which appear to be Compton-thin. For the X-ray-detected power-law sources with redshifts, an X-ray luminosity L_X ~ 10^44 erg/s marks a transition between low-luminosity, blue sources dominated by the host galaxy to high-luminosity, red power-law sources dominated by nuclear activity. X-ray-to-optical ratios, infrared variability, and 24 micron properties of the sample are consistent with the identification of infrared power-law sources as active nuclei, but a rough estimate is that only 22% of AGNs are selected by the power law criteria. Comparison of the power-law selection technique and various IRAC color criteria for identifying AGNs confirms that high-redshift samples selected via simple IRAC colors may be heavily contaminated by starlight-dominated objects.
We have combined data from the NOAO Deep Wide-Field Survey in Bootes and the Spitzer Space Telescope to determine basic properties for sixteen optically invisible MIPS 24um (OIMS) and thirty-five optically invisible radio (OIRS) soruces, including th
eir spectral energy distributions (SED) and luminosities. Most OIMSs possess steep power-law SEDs over lambda(rest) = 1-10 um, indicating the presence of obscured AGN in agreement with Spitzer spectroscopy. These objects are extremely luminous at rest-frame near and mid-IR (nu L_nu(5um) ~ 10^{38}-10^{39} 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 24um 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 L_K and stellar masses (M* ~ 10^{11} M_solar) assuming minimal AGN contribution. Roughly half of the OIRSs are not detected by Spitzers 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 3.6um and 4.5um 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.
A SST survey in the NOAO Deep-Wide Field in Bootes provides a complete, 8-micron-selected sample of galaxies to a limiting (Vega) magnitude of 13.5. In the 6.88 deg$^2$ field sampled, 79% of the 4867 galaxies have spectroscopic redshifts, allowing an
accurate determination of the local (z<0.3) galaxy luminosity function. Stellar and dust emission can be separated on the basis of observed galaxy colors. Dust emission (mostly PAH) accounts for 80% of the 8 micron luminosity, stellar photospheres account for 19%, and AGN emission accounts for roughly 1 %. A sub-sample of the 8 micron-selected galaxies have blue, early-type colors, but even most of these have significant PAH emission. The luminosity functions for the total 8 micron luminosity and for the dust emission alone are both well fit by Schechter functions. For the 8 micron luminosity function, the characteristic luminosity is u L_{ u}^*(8.0 micron) = 1.8 times 10^{10}$ Lsun while for the dust emission alone it is 1.6 x 10^{10}$ Lsun ull. The average 8 micron luminosity density at z<0.3 is 3.1 x 10^7 Lsun Mpc^{-3}, and the average luminosity density from dust alone is 2.5 x 10^7 Lsun Mpc^{-3}. This luminos ity arises predominantly from galaxies with 8 micron luminosities ($ u L_{ u}$) between $2times 10^9$ and $2 x 10^{10}$ Lsun, i.e., normal galaxies, not LIRGs or ULIRGs.
We analyze five epochs of Spitzer Space Telescope/Infrared Array Camera (IRAC) observations of the nearby spiral galaxy M33. Each epoch covered nearly a square degree at 3.6, 4.5, and 8.0 microns. The point source catalog from the full dataset contai
ns 37,650 stars. The stars have luminosities characteristic of the asymptotic giant branch and can be separated into oxygen-rich and carbon-rich populations by their [3.6] - [4.5] colors. The [3.6] - [8.0] colors indicate that over 80% of the stars detected at 8.0 microns have dust shells. Photometric comparison of epochs using conservative criteria yields a catalog of 2,923 variable stars. These variables are most likely long-period variables amidst an evolved stellar population. At least one-third of the identified carbon stars are variable.
