On R − W1 as a Diagnostic to Discover Obscured Active Galactic Nuclei in Wide-Area X-Ray Surveys

LaMassa, Stephanie; Civano, F.; Brusa, M.; Stern, Daniel; Glikman, Eilat; Gallagher, S. C.; Urry, C. Megan; Cales, Sabrina; Cappelluti, N.; Cardamone, Carolin N.; Comastri, A.; Farrah, D.; Greene, Jenny E.; Komossa, Stefanie; Merloni, A.; Mroczkowski, Tony; Natarajan, Priyamvada; Richards, Gordon T.; Salvato, M.; Schawinski, Kevin; Treister, Ezequiel

doi:10.3847/0004-637x/818/1/88

Cited by 24 publications

(31 citation statements)

References 143 publications

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“…24 Together, we have 13 X-ray measurements for our infraredselected sample, 12 of which we classified as AGNs and one as a galaxy. Figure 14 shows the HRs of our X-ray-detected sources, as compared with X-ray-detected AGNs in Stripe 82 from LaMassa et al (2016a). Comparing the mean HRs by type, we see the expected behavior where objects classified as Type-1 unobscured QSOs have a mean HR of −0.63, consistent with the average of −0.63 for radio-quiet quasars with Γ 2-10 =2.0 reported by Gallagher et al (2005).…”

Section: Hardness Ratiossupporting

confidence: 68%

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Luminous WISE-selected Obscured, Unobscured, and Red Quasars in Stripe 82^∗

Glikman

Lacy

LaMassa

et al. 2018

ApJ

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We present a spectroscopically complete sample of 147 infrared-color-selected active galactic nuclei (AGNs) down to a 22 μm flux limit of 20 mJy over the ∼270 deg 2 of the Sloan Digital Sky Survey Stripe 82 region. Most of these sources are in the QSO luminosity regime (L bol  10 12 L e ) and are found out to z;3. We classify the AGNs into three types, finding 57 blue, unobscured Type-1 (broad-lined) sources; 69 obscured, Type-2 (narrow-lined) sources; and 21 moderately reddened Type-1 sources (broad-lined and E(B − V )>0.25). We study a subset of this sample in X-rays and analyze their obscuration to find that our spectroscopic classifications are in broad agreement with low, moderate, and large amounts of absorption for Type-1, red Type-1, and Type-2 AGNs, respectively. We also investigate how their X-ray luminosities correlate with other known bolometric luminosity indicators such asand infrared luminosity (L 6μm ). While the X-ray correlation with L [O III] is consistent with previous findings, the most infrared-luminous sources appear to deviate from established relations such that they are either underluminous in X-rays or overluminous in the infrared. Finally, we examine the luminosity function evolution of our sample, and by AGN type, in combination with the complementary, infrared-selected, AGN sample of Lacy et al. (2013), spanning over two orders of magnitude in luminosity. We find that the two obscured populations evolve differently, with reddened Type-1 AGNs dominating the obscured AGN fraction (∼30%) for L 5μm >10 45 erg s −1 , while the fraction of Type-2 AGNs with L 5μm <10 45 erg s −1 rises sharply from 40% to 80% of the overall AGN population.

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Section: Hardness Ratiossupporting

confidence: 68%

“…LaMassa et al (2016a) computed HRs for X-ray-selected AGN candidates obeying the color cut R−W1>4 in the Stripe 82X catalog. Those measurements were done using BEHR, and we find matches to three sources in our sample.…”

Section: Hardness Ratiosmentioning

confidence: 99%

Luminous WISE-selected Obscured, Unobscured, and Red Quasars in Stripe 82^∗

Glikman

Lacy

LaMassa

et al. 2018

ApJ

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“…As demonstrated in LaMassa et al (2016b), obscured AGN between 0.5 < z < 1 tend to have R − W > 4 colors, which is a redshift regime where the traditional BPT diagnostic becomes untenable for observed-frame optical spectra. We perform BPT analysis on the low redshift sources (z < 0.5) that are spectroscopically classified as "Galaxies" but have X-ray luminosities or W 1 − W 2 colors consistent with AGN and relevant emission line fluxes with a S/N > 5 (see below).…”

Section: Description Of Multi-wavelength Information Inmentioning

confidence: 96%

“…Finally, we include a column that indicates the reddening of the source by calculating the optical to midinfrared R − W 1 color (LaMassa et al 2016b). We first Figure 11.…”

Section: Description Of Multi-wavelength Information Inmentioning

confidence: 99%

SDSS-IV eBOSS Spectroscopy of X-Ray and WISE AGNs in Stripe 82X: Overview of the Demographics of X-Ray- and Mid-infrared-selected Active Galactic Nuclei

LaMassa

Georgakakis

Vivek

et al. 2019

ApJ

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We report the results of a Sloan Digital Sky Survey-IV eBOSS program to target X-ray sources and mid-infrared-selected WISE AGN candidates in a 36.8 deg 2 region of Stripe 82. About half this survey (15.6 deg 2 ) covers the largest contiguous portion of the Stripe 82 X-ray survey. This program represents the largest spectroscopic survey of AGN candidates selected solely by their WISE colors. We combine this sample with X-ray and WISE AGN in the field identified via other sources of spectroscopy, producing a catalog of 4847 sources that is 82% complete to r ∼ 22. Based on X-ray luminosities or WISE colors, 4730 of these sources are AGN, with a median sample redshift of z ∼ 1. About 30% of the AGN are optically obscured (i.e., lack broad lines in their optical spectra). BPT analysis, however, indicates that 50% of the WISE AGN at z < 0.5 have emission line ratios consistent with star-forming galaxies, so whether they are buried AGN or star-forming galaxy contaminants is currently unclear. We find that 61% of X-ray AGN are not selected as MIR AGN, with 22% of X-ray AGN undetected by WISE. Most of these latter AGN have high X-ray luminosities (L x > 10 44 erg s −1 ), indicating that MIR selection misses a sizable fraction of the highest luminosity AGN, as well as lower luminosity sources where AGN heated dust is not dominating the MIR emission. Conversely, ∼58% of WISE AGN are undetected by X-rays, though we do not find that they are preferentially redder than the X-ray detected WISE AGN.

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“…Various optical and IR colour criteria have been used in the literature to identify red AGNs, using either Spitzer (e.g. Fiore et al 2009;Hickox et al 2007;LaMassa et al 2016;Donoso et al 2014) or WISE (Yan et al 2013) IR bands.…”

Section: Introductionmentioning

confidence: 99%

The XXL Survey

Masoura

Georgantopoulos

Mountrichas

et al. 2020

A&A

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The combination of optical and mid-infrared (MIR) photometry has been extensively used to select red active galactic nuclei (AGNs). Our aim is to explore the obscuration properties of these red AGNs with both X-ray spectroscopy and spectral energy distributions (SEDs). In this study, we re-visit the relation between optical/MIR extinction and X-ray absorption. We use IR selection criteria, specifically the W1 and W2 WISE bands, to identify 4798 AGNs in the XMM − XXL area (∼ 25 deg 2 ). Application of optical/MIR colours (r − W2 > 6) reveals 561 red AGNs (14%). Of these, 47 have available X-ray spectra with at least 50 net (backgroundsubtracted) counts per detector. For these sources, we construct SEDs from the optical to the MIR using the CIGALE code. The SED fitting shows that 44 of these latter 47 sources present clear signs of obscuration based on the AGN emission and the estimated inclination angle. Fitting the SED also reveals ten systems (∼ 20%) which are dominated by the galaxy. In these cases, the red colours are attributed to the host galaxy rather than AGN absorption. Excluding these ten systems from our sample and applying X-ray spectral fitting analysis shows that up to 76% (28/37) of the IR red AGNs present signs of X-ray absorption. Thus, there are nine sources (∼ 20% of the sample) that although optically red, are not substantially X-ray absorbed. Approximately 50% of these sources present broad emission lines in their optical spectra. We suggest that the reason for this apparent discrepancy is that the r-W2 criterion is sensitive to smaller amounts of obscuration relative to the X-ray spectroscopy. In conclusion, it appears that the majority of red AGNs present considerable obscuration levels as shown by their SEDs. Their X-ray absorption is moderate with a mean of N H ∼ 10 22 cm −2 .

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On R − W1 as a Diagnostic to Discover Obscured Active Galactic Nuclei in Wide-Area X-Ray Surveys

Cited by 24 publications

References 143 publications

Luminous WISE-selected Obscured, Unobscured, and Red Quasars in Stripe 82^∗

Luminous WISE-selected Obscured, Unobscured, and Red Quasars in Stripe 82^∗

SDSS-IV eBOSS Spectroscopy of X-Ray and WISE AGNs in Stripe 82X: Overview of the Demographics of X-Ray- and Mid-infrared-selected Active Galactic Nuclei

The XXL Survey

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On R − W1 as a Diagnostic to Discover Obscured Active Galactic Nuclei in Wide-Area X-Ray Surveys

Cited by 24 publications

References 143 publications

Luminous WISE-selected Obscured, Unobscured, and Red Quasars in Stripe 82∗

Luminous WISE-selected Obscured, Unobscured, and Red Quasars in Stripe 82∗

SDSS-IV eBOSS Spectroscopy of X-Ray and WISE AGNs in Stripe 82X: Overview of the Demographics of X-Ray- and Mid-infrared-selected Active Galactic Nuclei

The XXL Survey

Contact Info

Product

Resources

About

Luminous WISE-selected Obscured, Unobscured, and Red Quasars in Stripe 82^∗

Luminous WISE-selected Obscured, Unobscured, and Red Quasars in Stripe 82^∗