MID-INFRARED VARIABILITY FROM THE SPITZER DEEP WIDE-FIELD SURVEY

Journal Article · Thu Jun 10 00:00:00 EDT 2010 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/716/1/530· OSTI ID:21451129

Kozlowski, Szymon; Kochanek, Christopher S; Assef, Roberto J ^[1]; Stern, Daniel; Eisenhardt, P R; Gorjian, V; Griffith, R ^[2]; Ashby, Matthew L. N.; Brodwin, M ^[3]; Bock, J J; Borys, C ^[4]; Brand, K; Grogin, N ^[5]; Brown, M J. I. ^[6]; Cool, R ^[7]; Cooray, A ^[8]; Croft, S ^[9]; Dey, Arjun ^[10]; Gonzalez, A ^[11]; Ivison, R ^[12]

---

1. Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)
2. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Drive, Pasadena, CA 91109 (United States)
3. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States)
4. California Institute of Technology, Pasadena, CA 91125 (United States)
5. Space Telescope Science Institute, Baltimore, MD 21218 (United States)
6. School of Physics, Monash University, Clayton 3800, Victoria (Australia)
7. Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544 (United States)
8. University of California, Irvine, CA 92697 (United States)
9. University of California, Berkeley, CA 94720 (United States)
10. National Optical Astronomical Observatory, 950 North Cherry Avenue, Tucson, AZ 85719 (United States)
11. Department of Astronomy, University of Florida, Gainesville, FL 32611 (United States)
12. UK Astronomy Technology Centre, Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom)

We use the multi-epoch, mid-infrared Spitzer Deep Wide-Field Survey to investigate the variability of objects in 8.1 deg{sup 2} of the NOAO Deep Wide Field Survey Booetes field. We perform a Difference Image Analysis of the four available epochs between 2004 and 2008, focusing on the deeper 3.6 and 4.5 {mu}m bands. Out of 474, 179 analyzed sources, 1.1% meet our standard variability selection criteria that the two light curves are strongly correlated (r>0.8) and that their joint variance ({sigma}{sub 12}) exceeds that for all sources with the same magnitude by 2{sigma}. We then examine the mid-IR colors of the variable sources and match them with X-ray sources from the XBooetes survey, radio catalogs, 24 {mu}m selected active galactic nucleus (AGN) candidates, and spectroscopically identified AGNs from the AGN and Galaxy Evolution Survey (AGES). Based on their mid-IR colors, most of the variable sources are AGNs (76%), with smaller contributions from stars (11%), galaxies (6%), and unclassified objects, although most of the stellar, galaxy, and unclassified sources are false positives. For our standard selection criteria, 11%-12% of the mid-IR counterparts to X-ray sources, 24 {mu}m AGN candidates, and spectroscopically identified AGNs show variability. The exact fractions depend on both the search depth and the selection criteria. For example, 12% of the 1131 known z>1 AGNs in the field and 14%-17% of the known AGNs with well-measured fluxes in all four Infrared Array Camera bands meet our standard selection criteria. The mid-IR AGN variability can be well described by a single power-law structure function with an index of {gamma} {approx} 0.5 at both 3.6 and 4.5 {mu}m, and an amplitude of S {sub 0} {approx_equal} 0.1 mag on rest-frame timescales of 2 yr. The variability amplitude is higher for shorter rest-frame wavelengths and lower luminosities.

• OSTI ID: 21451129
• Journal Information: Astrophysical Journal, Vol. 716, Issue 1; Other Information: DOI: 10.1088/0004-637X/716/1/530; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
COSMIC X-RAY SOURCES
COSMOLOGY
GALACTIC EVOLUTION
GALAXIES
IMAGE PROCESSING
LUMINOSITY
QUASARS
STARS
STRUCTURE FUNCTIONS
COSMIC RADIO SOURCES
COSMIC RAY SOURCES
EVOLUTION
FUNCTIONS
OPTICAL PROPERTIES
PHYSICAL PROPERTIES
PROCESSING