Obscured and Unobscured Active Galactic Nuclei in the
                    <i>Spitzer Space Telescope</i>
                    First Look Survey

Lacy, Mark; Storrie-Lombardi, L. J.; Sajina, Anna; Appleton, P. N.; Armus, L.; Chapman, Scott; Choi, Philip; Fadda, D.; Fan, Fang; Frayer, David; Heinrichsen, I.; Hélou, G.; Im, Myungshin; Marleau, F.; Masci, Frank J.; Shupe, D. L.; Soifer, B. T.; Surace, J.; Teplitz, Harry I.; Wilson, Gillian; Yan, Lin

doi:10.1086/422816

Cited by 657 publications

(512 citation statements)

References 24 publications

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“…Motivated by the fact that X-rays can be absorbed in high column density environments, a number of groups developed mid-IR color selection techniques to identify AGN at high-z utilizing the bandpasses available on the Spitzer Space Telescope Lacy et al (2004) and Stern et al (2005). These were recently revisited by Donley et al (2012), under the premise that the previously developed color-selection "wedges" were contaminated by star-forming galaxies given deep enough IRAC data.…”

Section: Agn Contentmentioning

confidence: 99%

Dusty star-forming galaxies at high redshift

2014

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Far-infrared and submillimeter wavelength surveys have now established the important role of dusty, star-forming galaxies (DSFGs) in the assembly of stellar mass and the evolution of massive galaxies in the Universe. The brightest of these galaxies have infrared luminosities in excess of 10 13 L with implied star-formation rates of thousands of solar masses per year. They represent the most intense starbursts in the Universe, yet many are completely optically obscured. Their easy detection at submm wavelengths is due to dust heated by ultraviolet radiation of newly forming stars. When summed up, all of the dusty, star-forming galaxies in the Universe produce an infrared radiation field that has an equal energy density as the direct starlight emission from all galaxies visible at ultraviolet and optical wavelengths. The bulk of this infrared extragalactic background light emanates from galaxies as diverse as gas-rich disks to mergers of intense starbursting galaxies. Major advances in far-infrared instrumentation in recent years, both spacebased and ground-based, has led to the detection of nearly a million DSFGs, yet our understanding of the underlying astrophysics that govern the start and end of the dusty starburst phase is still in nascent stage. This review is aimed at summarizing the current status of DSFG studies, focusing especially on the detailed characterization of the bestunderstood subset (submillimeter galaxies, who were summarized in the last review of this field over a decade ago, Blain et al. 2002), but also the selection and characterization of more recently discovered DSFG populations. We review DSFG population statistics, their physical properties including dust, gas and stellar contents, their environments, and current theoretical models related to the formation and evolution of these galaxies.

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Section: Agn Contentmentioning

confidence: 99%

Dusty star-forming galaxies at high redshift

2014

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“…Richards et al (2006) characterized the diversity in SEDs among Type 1 QSOs, using 259 objects with Spitzer and Sloan data, and showed that a mean SED can estimate the bolometric luminosities of individual quasars to within 50%. Lacy et al (2004) and Stern et al (2005) have utilized the combination of IRAC imaging and SDSS data to define mid-IR color criteria to identify AGN. The selection is based purely on IRAC colors.…”

Section: Qsos and Unification Theoriesmentioning

confidence: 99%

The Spitzer View of the Extragalactic Universe

Soifer

Hélou

Werner

2008

Annu. Rev. Astron. Astrophys.

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The Spitzer Space Telescope was launched in August 2003. Scientists from around the world have applied its orders-of-magnitude gain in imaging and spectroscopic capability to a wide array of topics in extragalactic research. Spitzer studies have found massive galaxies at redshifts greater than 6, resolved the cosmic background at 200 μm > λ > 20 μm into the dusty infraredluminous galaxies that comprise it, directly detected dust-enshrouded star formation, and measured the star formation history of the universe to z > 3. In this review we examine a small fraction of the extragalactic studies from Spitzer that have been conducted in its first three years of operations.

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“…It can select a relatively pure sample of AGNs with little contamination from star-forming galaxies but is generally limited to the mostluminous sources (e.g., Polletta et al 2008). IRAC color-color selection applies color cuts in the IRAC color space to identify AGNs (e.g., Lacy et al 2004;Stern et al 2005). This method is based on the IRAC color properties of optically selected QSOs and AGNs, and it tends to have significant contamination from star-forming galaxies when applied to deep mid-IR data (e.g., Cardamone et al 2008;Georgantopoulos et al 2008;Brusa et al 2010).…”

Section: Introductionmentioning

confidence: 99%

REVEALING A POPULATION OF HEAVILY OBSCURED ACTIVE GALACTIC NUCLEI ATz≈ 0.5-1 IN THE CHANDRA DEEP FIELD-SOUTH

Brandt

Xue

Alexander

et al. 2011

ApJ

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Heavily obscured (N H 3 × 10 23 cm −2 ) Active Galactic Nuclei (AGNs) not detected in even the deepest X-ray surveys are often considered to be comparably numerous to the unobscured and moderately obscured AGNs. Such sources are required to fit the cosmic X-ray background (XRB) emission in the 10-30 keV band. We identify a numerically significant population of heavily obscured AGNs at z ≈ 0.5-1 in the Chandra Deep Field-South (CDF-S) and Extended Chandra Deep Field-South by selecting 242 X-ray undetected objects with infrared-based star formation rates (SFRs) substantially higher (a factor of 3.2 or more) than their SFRs determined from the UV after correcting for dust extinction. An X-ray stacking analysis of 23 candidates in the central CDF-S region using the 4 Ms Chandra data reveals a hard X-ray signal with an effective power-law photon index of Γ = 0.6 +0.3 −0.4 , indicating a significant contribution from obscured AGNs. Based on Monte Carlo simulations, we conclude that 74 ± 25% of the selected galaxies host obscured AGNs, within which ≈ 95% are heavily obscured and ≈ 80% are Compton-thick (CT; N H > 1.5 × 10 24 cm −2 ). The heavily obscured objects in our sample are of moderate intrinsic X-ray luminosity [≈ (0.9-4) × 10 42 erg s −1 in the 2-10 keV band]. The space density of the CT AGNs is (1.6 ± 0.5) × 10 −4 Mpc −3 . The z ≈ 0.5-1 CT objects studied here are expected to contribute ≈ 1% of the total XRB flux in the 10-30 keV band, and they account for ≈ 5-15% of the emission in this energy band expected from all CT AGNs according to population-synthesis models. In the 6-8 keV band, the stacked signal of the 23 heavily obscured candidates accounts for < 5% of the unresolved XRB flux, while the unresolved ≈ 25% of the XRB in this band can probably be explained by a stacking analysis of the X-ray undetected optical galaxies in the CDF-S (a 2.5 σ stacked signal). We discuss prospects to identify such heavily obscured objects using future hard X-ray observatories.

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Obscured and Unobscured Active Galactic Nuclei in the Spitzer Space Telescope First Look Survey

Cited by 657 publications

References 24 publications

Dusty star-forming galaxies at high redshift

Dusty star-forming galaxies at high redshift

The Spitzer View of the Extragalactic Universe

REVEALING A POPULATION OF HEAVILY OBSCURED ACTIVE GALACTIC NUCLEI ATz≈ 0.5-1 IN THE CHANDRA DEEP FIELD-SOUTH

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