Spitzer Power-Law Active Galactic Nucleus Candidates in the Chandra Deep Field-North

By J. Donley, G. Rieke, P. Pérez-González, J. Rigby, A. Alonso-Herrero, U. Arizona, U. Madrid, Spain, Instituto de Estructura de la Materia, Csic. 2007

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We define a sample of 62 galaxies in the Chandra Deep Field-North whose Spitzer IRAC SEDs exhibit the characteristic power-law emission expected of luminous AGNs. We study the multiwavelength properties of this sample and compare the AGNs selected in this way to those selected via other Spitzer color-color criteria. Only 55% of the power-law galaxies are detected in the X-ray catalog at exposures of >0.5 Ms, although a search for faint emission results in the detection of 85% of the power-law galaxies at the ≥2.5 σ detection level. Most of the remaining galaxies are likely to host AGNs that are heavily obscured in the X-ray. Because the power-law selection requires the AGNs to be energetically dominant in the near- and mid-infrared, the power-law galaxies comprise a significant fraction of the Spitzer-detected AGN population at high luminosities and redshifts. The high 24 μm detection fraction also points to a luminous population. The power-law galaxies comprise a subset of color-selected AGN candidates. A comparison with various mid-infrared color selection criteria demonstrates that while the color-selected samples contain a larger fraction of the X-ray-luminous AGNs, there is evidence that these selection techniques also suffer from a higher degree of contamination by star-forming galaxies in the deepest exposures. Considering only those power-law galaxies detected in the X-ray catalog, we derive an obscured fraction of 68% (2 : 1). Including all of the power-law galaxies suggests an obscured fraction of <81% (4 : 1).

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/46b6fd786232d2b73b336023c2c4065dce5e6296

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LOW-RESOLUTION SPECTRAL TEMPLATES FOR ACTIVE GALACTIC NUCLEI AND GALAXIES FROM 0.03 TO 30 μm (2010, methodology): “In an earlier work, Donley et al. (2008) used objects in the GOODS-S field (Giavalisco et al. 2004) to compare the reliability of these two AGN selection criteria in addition to the power-law galaxies selection method of Alonso-Herrero et al. (2006) and Donley et al. (2007).”
MID-INFRARED SELECTION OF ACTIVE GALACTIC NUCLEI WITH THE WIDE-FIELD INFRARED SURVEY EXPLORER. I. CHARACTERIZING WISE-SELECTED ACTIVE GALACTIC NUCLEI IN COSMOS (2012, methodology): “For example, Donley et al. (2007), using data from the Ms Chandra Deep FieldNorth (Alexander et al. 2003), find that the mid-infrared selection efficiency increases from ∼ 14% at L0.”
Multiwavelength Study of Massive Galaxies at z ~ 2. II. Widespread Compton-thick Active Galactic Nuclei and the Concurrent Growth of Black Holes and Bulges (2007, background): “…factor of∼ 2 higher than that of X-ray sources individually detected in X-rays in GOODS-S (Zheng et al 2004), a factor≈ 10 higher than X-ray detected submillimeter-emitting galaxies (Alexander et al. 2003b), and ≈ 20 times higher than X-ray undetected power-law AGN candidates (Donley et al. 2007).”
Galaxy pairs in the Sloan Digital Sky Survey – IX. Merger-induced AGN activity as traced by the Wide-field Infrared Survey Explorer (2014, background): “…over the past decade have demonstrated the power and reliability of mid-infrared observations in discovering optically hidden AGNs (e.g., Lacy et al. 2004; Stern et al. 2005; Donley et al. 2007; Hickox et al. 2007; Donley et al. 2008; Eckart et al. 2010; Stern et al. 2012; Mateos et al. 2013).”
DETERMINING STAR FORMATION RATES FOR INFRARED GALAXIES (2008, background): “Our templates have played important roles in a number of recent studies (Donley et al. 2007; Rigby et al. 2008; Seymour et al. 2008; Donley et al. 2008).”
A physical model for z∼ 2 dust-obscured galaxies (2009, methodology): “With the launch of the Spitzer Space Telescope, surveys at 24 μm have uncovered a population of ULIRGs at z ∼ 2 (e.g. Rigby et al. 2004; Donley et al. 2007; Yan et al. 2007; Farrah et al. 2008; Soifer, Helou & Werner 2008; Lonsdale et al. 2009; Huang et al. 2009, and references therein).”
AN ATLAS OF GALAXY SPECTRAL ENERGY DISTRIBUTIONS FROM THE ULTRAVIOLET TO THE MID-INFRARED (2013, methodology): “In Figure 12 we plot our spectrum of IC 4553 (Arp 220), along with other IC 4553 templates from the recent literature (Chary & Elbaz 2001; Donley et al. 2007; Polletta et al. 2007; Rieke et al. 2009).”
The Stellar Mass Assembly of Galaxies from z = 0 to z = 4: Analysis of a Sample Selected in the Rest-Frame Near-Infrared with Spitzer (2007, methodology): “Other selection procedures have been used to identify obscured AGNs, such as the presence of a power-law spectrum in the IRAC bands (Alonso-Herrero et al. 2004; Donley et al. 2007).”
Cosmic X-ray surveys of distant active galaxies (2015, methodology): “Power-law selection from MIR photometric and/or MIR spectroscopic data (e.g., Alonso-Herrero et al 2006; Donley et al 2007; Alexander et al 2008; Donley et al 2008; Park et al 2010).”
IDENTIFYING LUMINOUS ACTIVE GALACTIC NUCLEI IN DEEP SURVEYS: REVISED IRAC SELECTION CRITERIA (2012, methodology): “…galaxies While the purely star-forming templates shown in Figures 2 and 3 lie outside of the power-law region in IRAC color space, they enter the Lacy et al. (2004, 2007) and Stern et al. (2005) AGN selection wedges at both low and high redshift (Barmby et al. 2006; Donley et al. 2007, 2008).”
Multiwavelength Study of Massive Galaxies at z~2. I. Star Formation and Galaxy Growth (2007, background): “This could be due to additional radio emission from an AGN (despite nondetection at X-ray wavelengths), as suggested also by Donley et al. (2007), mostly in lower redshift sources.”
A CORRELATION BETWEEN STAR FORMATION RATE AND AVERAGE BLACK HOLE ACCRETION IN STAR-FORMING GALAXIES (2013, background): “…effectively identify obscured AGN at moderate redshift (Gorjian et al. 2008; Assef et al. 2010), since mid-IR wavelengths are not as strongly affected by obscuration as the optical or UV (e.g. Lacy et al. 2004; Stern et al. 2005; Donley et al. 2007; Hickox et al. 2007; Goulding & Alexander 2009).”
SPECTRAL ENERGY DISTRIBUTIONS OF LOCAL LUMINOUS AND ULTRALUMINOUS INFRARED GALAXIES (2012, background): “2) > 0 to select galaxies with power-law SED shape in the near-IR, corresponding to Fν spectral slope of 0.4 (Kartaltepe et al. 2010; Alonso-Herrero et al. 2006; Donley et al. 2007).”
A NEW DIAGNOSTIC OF ACTIVE GALACTIC NUCLEI: REVEALING HIGHLY ABSORBED SYSTEMS AT REDSHIFT >0.3 (2011, background): “Another such tracer is mid-infrared continuum emission originating from hot dust heated by the AGN (e.g., Lacy et al. 2004; Stern et al. 2005; Donley et al. 2007).”
A Highly Complete Spectroscopic Survey of the GOODS-N Field (2008, background): “We can see from our data that this color-color plot is quite poor at picking out lower luminosity AGNs (see also Barmby et al. 2006; Treister et al. 2006; Donley et al. 2007; Cardamone et al. 2008), while also missing one of the more luminous X-ray AGNs and six of the high radio power sources.”