Identifying Luminous AGN in Deep Surveys: Revised IRAC Selection Criteria
J. L. Donley, A. M. Koekemoer, M. Brusa, P. Capak, C. N. Cardamone, F. Civano, O. Ilbert, C. D. Impey, J. S. Kartaltepe, T. Miyaji, M. Salvato, D. B. Sanders, J… 展开作者
J. L. Donley, A. M. Koekemoer, M. Brusa, P. Capak, C. N. Cardamone, F. Civano, O. Ilbert, C. D. Impey, J. S. Kartaltepe, T. Miyaji, M. Salvato, D. B. Sanders, J. R. Trump, G. Zamorani
Spitzer IRAC selection is a powerful tool for identifying luminous AGN. For deep IRAC data, however, the AGN selection wedges currently in use are heavily contaminated by star-forming galaxies, especially at high redshift. Using the large samples of luminous AGN and high-redshift star-forming galaxies in COSMOS, we redefine the AGN selection criteria for use in deep IRAC surveys. The new IRAC criteria are designed to be both highly complete and reliable, and incorporate the best aspects of the current AGN selection wedges and of infrared power-law selection while excluding high redshift star-forming galaxies selected via the BzK, DRG, LBG, and SMG criteria. At QSO-luminosities of log L(2-10 keV) (ergs/s) > 44, the new IRAC criteria recover 75% of the hard X-ray and IRAC-detected XMM-COSMOS sample, yet only 38% of the IRAC AGN candidates have X-ray counterparts, a fraction that rises to 52% in regions with Chandra exposures of 50-160 ks. X-ray stacking of the individually X-ray non-detected AGN candidates leads to a hard X-ray signal indicative of heavily obscured to mildly Compton-thick obscuration (log N_H (cm^-2) = 23.5 +/- 0.4). While IRAC selection recovers a substantial fraction of luminous unobscured and obscured AGN, it is incomplete to low-luminosity and host-dominated AGN.
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Ultradeep Infrared Array Camera Observations of sub-L* z~7 and z~8 Galaxies in the Hubble Ultra Deep Field: the Contribution of Low-Luminosity Galaxies to the Stellar Mass Density and Reionization
We study the Spitzer Infrared Array Camera (IRAC) mid-infrared (rest-frame optical) fluxes of 14 newly WFC3/IR-detected z=7 z_{850} -dropout galaxies and 5 z=8 Y_{105} -dropout galaxies. The WFC3/IR depth and spatial resolution allow accurate removal of contaminating foreground light, enabling reliable flux measurements at 3.6 micron and 4.5 micron. None of the galaxies are detected to [3.6]=26.9 (AB, 2 sigma), but a stacking analysis reveals a robust detection for the z_{850} -dropouts and an upper limit for the Y_{105} -dropouts. We construct average broadband SEDs using the stacked ACS, WFC…
