Astron. J., 145, 55 (2013/March-0)
Characterizing the mid-infrared extragalactic sky with WISE and SDSS.
YAN L., DONOSO E., TSAI C.-W., STERN D., ASSEF R.J., EISENHARDT P., BLAIN A.W., CUTRI R., JARRETT T., STANFORD S.A., WRIGHT E., BRIDGE C. and RIECHERS D.A.
Abstract (from CDS):
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/NW1>7σ, but only 18.9% at 22 µm with S/NW4> 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/deg2. (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/deg2 at S/NW4 ≥ 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.
galaxies: evolution - galaxies: high-redshift - galaxies: starburst - infrared: galaxies
ULAS J1120+0461 is ULAS J112001.48+064124.3 in Simbad. IRAS 0872+3915 is a misprint for IRAS 08572+3915.
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