Mid-infrared variability from the spitzer deep wide-field survey

Szymon Kozłowski, Christopher S. Kochanek, Daniel Stern, Matthew L N Ashby, Roberto J. Assef, J. J. Bock, C. Borys, K. Brand, M. Brodwin, M. J I Brown, R. Cool, A. Cooray, S. Croft, Arjun Dey, P. R. Eisenhardt, A. Gonzalez, V. Gorjian, R. Griffith, N. Grogin, R. Ivison & 13 others J. Jacob, Buell Tomasson Jannuzi, A. Mainzer, L. Moustakas, H. Röttgering, N. Seymour, H. A. Smith, S. A. Stanford, J. R. Stauffer, I. S. Sullivan, W. Van Breugel, S. P. Willner, E. L. Wright

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

We use the multi-epoch, mid-infrared Spitzer Deep Wide-Field Survey to investigate the variability of objects in 8.1 deg2 of the NOAO Deep Wide Field Survey Boötes 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 μm 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 (σ12) exceeds that for all sources with the same magnitude by 2σ. We then examine the mid-IR colors of the variable sources and match them with X-ray sources from the XBoötes survey, radio catalogs, 24 μm 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 μm 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 γ ≈ 0.5 at both 3.6 and 4.5 μm, and an amplitude of S 0 ≃ 0.1 mag on rest-frame timescales of 2 yr. The variability amplitude is higher for shorter rest-frame wavelengths and lower luminosities.

Original languageEnglish (US)
Pages (from-to)530-543
Number of pages14
JournalAstrophysical Journal
Volume716
Issue number1
DOIs
StatePublished - 2010
Externally publishedYes

Fingerprint

field survey
active galactic nuclei
galaxies
image analysis
time measurement
power law
color
radio
wavelength
timescale
light curve
catalogs
x rays
cameras
luminosity
stars
wavelengths

Keywords

  • Cosmology: observations
  • Galaxies: active
  • Infrared: galaxies
  • Quasars: general

ASJC Scopus subject areas

  • Space and Planetary Science
  • Astronomy and Astrophysics

Cite this

Kozłowski, S., Kochanek, C. S., Stern, D., Ashby, M. L. N., Assef, R. J., Bock, J. J., ... Wright, E. L. (2010). Mid-infrared variability from the spitzer deep wide-field survey. Astrophysical Journal, 716(1), 530-543. https://doi.org/10.1088/0004-637X/716/1/530

Mid-infrared variability from the spitzer deep wide-field survey. / Kozłowski, Szymon; Kochanek, Christopher S.; Stern, Daniel; Ashby, Matthew L N; Assef, Roberto J.; Bock, J. J.; Borys, C.; Brand, K.; Brodwin, M.; Brown, M. J I; Cool, R.; Cooray, A.; Croft, S.; Dey, Arjun; Eisenhardt, P. R.; Gonzalez, A.; Gorjian, V.; Griffith, R.; Grogin, N.; Ivison, R.; Jacob, J.; Jannuzi, Buell Tomasson; Mainzer, A.; Moustakas, L.; Röttgering, H.; Seymour, N.; Smith, H. A.; Stanford, S. A.; Stauffer, J. R.; Sullivan, I. S.; Van Breugel, W.; Willner, S. P.; Wright, E. L.

In: Astrophysical Journal, Vol. 716, No. 1, 2010, p. 530-543.

Research output: Contribution to journalArticle

Kozłowski, S, Kochanek, CS, Stern, D, Ashby, MLN, Assef, RJ, Bock, JJ, Borys, C, Brand, K, Brodwin, M, Brown, MJI, Cool, R, Cooray, A, Croft, S, Dey, A, Eisenhardt, PR, Gonzalez, A, Gorjian, V, Griffith, R, Grogin, N, Ivison, R, Jacob, J, Jannuzi, BT, Mainzer, A, Moustakas, L, Röttgering, H, Seymour, N, Smith, HA, Stanford, SA, Stauffer, JR, Sullivan, IS, Van Breugel, W, Willner, SP & Wright, EL 2010, 'Mid-infrared variability from the spitzer deep wide-field survey', Astrophysical Journal, vol. 716, no. 1, pp. 530-543. https://doi.org/10.1088/0004-637X/716/1/530
Kozłowski S, Kochanek CS, Stern D, Ashby MLN, Assef RJ, Bock JJ et al. Mid-infrared variability from the spitzer deep wide-field survey. Astrophysical Journal. 2010;716(1):530-543. https://doi.org/10.1088/0004-637X/716/1/530
Kozłowski, Szymon ; Kochanek, Christopher S. ; Stern, Daniel ; Ashby, Matthew L N ; Assef, Roberto J. ; Bock, J. J. ; Borys, C. ; Brand, K. ; Brodwin, M. ; Brown, M. J I ; Cool, R. ; Cooray, A. ; Croft, S. ; Dey, Arjun ; Eisenhardt, P. R. ; Gonzalez, A. ; Gorjian, V. ; Griffith, R. ; Grogin, N. ; Ivison, R. ; Jacob, J. ; Jannuzi, Buell Tomasson ; Mainzer, A. ; Moustakas, L. ; Röttgering, H. ; Seymour, N. ; Smith, H. A. ; Stanford, S. A. ; Stauffer, J. R. ; Sullivan, I. S. ; Van Breugel, W. ; Willner, S. P. ; Wright, E. L. / Mid-infrared variability from the spitzer deep wide-field survey. In: Astrophysical Journal. 2010 ; Vol. 716, No. 1. pp. 530-543.
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abstract = "We use the multi-epoch, mid-infrared Spitzer Deep Wide-Field Survey to investigate the variability of objects in 8.1 deg2 of the NOAO Deep Wide Field Survey Bo{\"o}tes 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 μm 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 (σ12) exceeds that for all sources with the same magnitude by 2σ. We then examine the mid-IR colors of the variable sources and match them with X-ray sources from the XBo{\"o}tes survey, radio catalogs, 24 μm 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 μm 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 γ ≈ 0.5 at both 3.6 and 4.5 μm, and an amplitude of S 0 ≃ 0.1 mag on rest-frame timescales of 2 yr. The variability amplitude is higher for shorter rest-frame wavelengths and lower luminosities.",
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AU - Kozłowski, Szymon

AU - Kochanek, Christopher S.

AU - Stern, Daniel

AU - Ashby, Matthew L N

AU - Assef, Roberto J.

AU - Bock, J. J.

AU - Borys, C.

AU - Brand, K.

AU - Brodwin, M.

AU - Brown, M. J I

AU - Cool, R.

AU - Cooray, A.

AU - Croft, S.

AU - Dey, Arjun

AU - Eisenhardt, P. R.

AU - Gonzalez, A.

AU - Gorjian, V.

AU - Griffith, R.

AU - Grogin, N.

AU - Ivison, R.

AU - Jacob, J.

AU - Jannuzi, Buell Tomasson

AU - Mainzer, A.

AU - Moustakas, L.

AU - Röttgering, H.

AU - Seymour, N.

AU - Smith, H. A.

AU - Stanford, S. A.

AU - Stauffer, J. R.

AU - Sullivan, I. S.

AU - Van Breugel, W.

AU - Willner, S. P.

AU - Wright, E. L.

PY - 2010

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N2 - We use the multi-epoch, mid-infrared Spitzer Deep Wide-Field Survey to investigate the variability of objects in 8.1 deg2 of the NOAO Deep Wide Field Survey Boötes 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 μm 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 (σ12) exceeds that for all sources with the same magnitude by 2σ. We then examine the mid-IR colors of the variable sources and match them with X-ray sources from the XBoötes survey, radio catalogs, 24 μm 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 μm 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 γ ≈ 0.5 at both 3.6 and 4.5 μm, and an amplitude of S 0 ≃ 0.1 mag on rest-frame timescales of 2 yr. The variability amplitude is higher for shorter rest-frame wavelengths and lower luminosities.

AB - We use the multi-epoch, mid-infrared Spitzer Deep Wide-Field Survey to investigate the variability of objects in 8.1 deg2 of the NOAO Deep Wide Field Survey Boötes 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 μm 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 (σ12) exceeds that for all sources with the same magnitude by 2σ. We then examine the mid-IR colors of the variable sources and match them with X-ray sources from the XBoötes survey, radio catalogs, 24 μm 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 μm 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 γ ≈ 0.5 at both 3.6 and 4.5 μm, and an amplitude of S 0 ≃ 0.1 mag on rest-frame timescales of 2 yr. The variability amplitude is higher for shorter rest-frame wavelengths and lower luminosities.

KW - Cosmology: observations

KW - Galaxies: active

KW - Infrared: galaxies

KW - Quasars: general

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