%0 Journal Article %A Yan, L %A Donoso, E %A Tsai, C-W %A Stern, D %A Assef, RJ %A Eisenhardt, P %A Blain, Andrew W. %A Cutri, R %A Jarrett, T %A Stanford, SA %A Wright, E %A Bridge, C %A Riechers, DA %D 2017 %T Characterizing the Mid-Infrared Extragalactic Sky with WISE and SDSS %U https://figshare.le.ac.uk/articles/journal_contribution/Characterizing_the_Mid-Infrared_Extragalactic_Sky_with_WISE_and_SDSS/10235489 %2 https://figshare.le.ac.uk/ndownloader/files/18470573 %K Science & Technology %K Physical Sciences %K Astronomy & Astrophysics %K galaxies: evolution %K galaxies: high-redshift %K galaxies: starburst %K infrared: galaxies %K ACTIVE GALACTIC NUCLEI %K SPECTROSCOPIC TARGET SELECTION %K IRAC SHALLOW SURVEY %K 7TH DATA RELEASE %K X-RAY %K LUMINOSITY FUNCTION %K DEEP SURVEY %K MU-M %K GALAXIES %K REDSHIFT %X The Wide-field Infrared Survey Explorer (WISE) has completed its all-sky survey in four channels at 3.4-22 μm, detecting hundreds of millions of objects. We merge the WISE mid-infrared data with optical data from the Sloan Digital Sky Survey (SDSS) and provide a phenomenological characterization of WISE extragalactic sources. WISE is most sensitive at 3.4 μm (W1) and least sensitive at 22 μm (W4). The W1 band probes massive early-type galaxies out to z 1. This is more distant than SDSS identified early-type galaxies, consistent with the fact that 28% of 3.4 μm sources have faint or no r-band counterparts (r > 22.2). In contrast, 92%-95% of 12 μm and 22 μm sources have SDSS optical counterparts with r ≤ 22.2. WISE 3.4 μm detects 89.8% of the entire SDSS QSO catalog at S/N W1 >7σ, but only 18.9% at 22 μm with S/N W4 > 5σ. We show that WISE colors alone are effective in isolating stars (or local early-type galaxies), star-forming galaxies, and strong active galactic nuclei (AGNs)/QSOs at z 3. We highlight three major applications of WISE colors: (1) Selection of strong AGNs/QSOs at z ≤ 3 using W1 – W2 > 0.8 and W2 < 15.2 criteria, producing a better census of this population. The surface density of these strong AGN/QSO candidates is 67.5 ± 0.14 deg–2. (2) Selection of dust-obscured, type-2 AGN/QSO candidates. We show that WISE W1 – W2 > 0.8, W2 < 15.2 combined with r – W2 > 6 (Vega) colors can be used to identify type-2 AGN candidates. The fraction of these type-2 AGN candidates is one-third of all WISE color-selected AGNs. (3) Selection of ultraluminous infrared galaxies (ULIRGs) at z ~ 2 with extremely red colors, r– W4 > 14 or well-detected 22 μm sources lacking detections in the 3.4 and 4.6 μm bands. The surface density of z ~ 2 ULIRG candidates selected with r – W4 > 14 is 0.9 ± 0.07 deg–2 at S/N W4 ≥ 5 (the corresponding, lowest flux density of 2.5 mJy), which is consistent with that inferred from smaller area Spitzer surveys. Optical spectroscopy of a small number of these high-redshift ULIRG candidates confirms our selection, and reveals a possible trend that optically fainter or r – W4 redder candidates are at higher redshifts. %I University of Leicester