Mid-infrared selection of active galaxies

Daniel Stern, Peter Eisenhardt, Varoujan Gorjian, Christopher S. Kochanek, Nelson Caldwell, Daniel Eisenstein, Mark Brodwin, Michael J I Brown, Richard Cool, Arjun Dey, Paul Green, Buell Tomasson Jannuzi, Stephen S. Murray, Michael A. Pahre, S. P. Willner

Research output: Contribution to journalArticle

611 Citations (Scopus)

Abstract

Mid-infrared photometry provides a robust technique for identifying active galaxies. While the ultraviolet to mid-infrared (λ ≲ 5 μm) continuum of stellar populations is dominated by the composite blackbody curve and peaks at approximately 1.6 μm, the ultraviolet to mid-infrared continuum of active galactic nuclei (AGNs) is dominated by a power law. Consequently, with a sufficient wavelength baseline, one can easily distinguish AGNs from stellar populations. Mirroring the tendency of AGNs to be bluer than galaxies in the ultraviolet, where galaxies (and stars) sample the blue, rising portion of stellar spectra, AGNs tend to be redder than galaxies in the mid-infrared, where galaxies sample the red, falling portion of the stellar spectra. We report on Spitzer Space Telescope mid-infrared colors, derived from the IRAC Shallow Survey, of nearly 10,000 spectroscopically identified sources from the AGN and Galaxy Evolution Survey. On the basis of this spectroscopic sample, we find that simple mid-infrared color criteria provide remarkably robust separation of active galaxies from normal galaxies and Galactic stars, with over 80% completeness and less than 20% contamination. Considering only broad-lined AGNs, these mid-infrared color criteria identify over 90% of spectroscopically identified quasars and Seyfert 1 galaxies. Applying these color criteria to the full imaging data set, we discuss the implied surface density of AGNs and find evidence for a large population of optically obscured active galaxies.

Original languageEnglish (US)
Pages (from-to)163-168
Number of pages6
JournalAstrophysical Journal
Volume631
Issue number1 I
DOIs
StatePublished - Sep 20 2005
Externally publishedYes

Fingerprint

active galaxies
active galactic nuclei
galaxies
color
stellar spectra
power law
continuums
stars
infrared photometry
Space Infrared Telescope Facility
wavelength
completeness
falling
quasars
tendencies
contamination
composite materials
curves
wavelengths

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Stern, D., Eisenhardt, P., Gorjian, V., Kochanek, C. S., Caldwell, N., Eisenstein, D., ... Willner, S. P. (2005). Mid-infrared selection of active galaxies. Astrophysical Journal, 631(1 I), 163-168. https://doi.org/10.1086/432523

Mid-infrared selection of active galaxies. / Stern, Daniel; Eisenhardt, Peter; Gorjian, Varoujan; Kochanek, Christopher S.; Caldwell, Nelson; Eisenstein, Daniel; Brodwin, Mark; Brown, Michael J I; Cool, Richard; Dey, Arjun; Green, Paul; Jannuzi, Buell Tomasson; Murray, Stephen S.; Pahre, Michael A.; Willner, S. P.

In: Astrophysical Journal, Vol. 631, No. 1 I, 20.09.2005, p. 163-168.

Research output: Contribution to journalArticle

Stern, D, Eisenhardt, P, Gorjian, V, Kochanek, CS, Caldwell, N, Eisenstein, D, Brodwin, M, Brown, MJI, Cool, R, Dey, A, Green, P, Jannuzi, BT, Murray, SS, Pahre, MA & Willner, SP 2005, 'Mid-infrared selection of active galaxies', Astrophysical Journal, vol. 631, no. 1 I, pp. 163-168. https://doi.org/10.1086/432523
Stern D, Eisenhardt P, Gorjian V, Kochanek CS, Caldwell N, Eisenstein D et al. Mid-infrared selection of active galaxies. Astrophysical Journal. 2005 Sep 20;631(1 I):163-168. https://doi.org/10.1086/432523
Stern, Daniel ; Eisenhardt, Peter ; Gorjian, Varoujan ; Kochanek, Christopher S. ; Caldwell, Nelson ; Eisenstein, Daniel ; Brodwin, Mark ; Brown, Michael J I ; Cool, Richard ; Dey, Arjun ; Green, Paul ; Jannuzi, Buell Tomasson ; Murray, Stephen S. ; Pahre, Michael A. ; Willner, S. P. / Mid-infrared selection of active galaxies. In: Astrophysical Journal. 2005 ; Vol. 631, No. 1 I. pp. 163-168.
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