The $XXL$ survey: XL. Obscuration properties of red AGN in $XXL-N$

Abstract

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 ($\sim 25$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 (background-subtracted) 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 ($\sim 20\%$) 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 ($\sim 20\%$ 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 ${\mathrm{N}}_{\mathrm{H}}\sim 10^{22}\mathrm{c}{\mathrm{m}}^{-2}$.

arXiv commentA&A accepted, 37 pages, 51 figures, 7 tables

References in corpus (48)

• Stellar population synthesis at the resolution of 2003
• The Wide-field Infrared Survey Explorer (WISE): Mission Description and Initial On-orbit Performance
• The Dust Content and Opacity of Actively Star-Forming Galaxies
• The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections
• Galaxy and Mass Assembly (GAMA): survey diagnostics and core data release
• Analysis of galaxy SEDs from far-UV to far-IR with CIGALE: Studying a SINGS test sample
• Revisiting the Unified Model of Active Galactic Nuclei
• Mid-Infrared Selection of AGN with the Wide-Field Infrared Survey Explorer. I. Characterizing WISE-Selected AGN in COSMOS
• AGN Dusty Tori: II. Observational Implications of Clumpiness
• The Herschel Multi-tiered Extragalactic Survey: HerMES
• Toward the Standard Population Synthesis Model of the X-Ray Background: Evolution of X-Ray Luminosity and Absorption Functions of Active Galactic Nuclei Including Compton-Thick Populations
• AGN Dusty Tori: I. Handling of Clumpy Media
• Revisiting the Infrared Spectra of Active Galactic Nuclei with a New Torus Emission Model
• A Hubble Space Telescope Imaging Survey of Nearby Active Glactic Nuclei
• Star Formation and Dust Attenuation Properties in Galaxies from a Statistical UV-to-FIR Analysis
• The WFCAM Science Archive
• Obscured Active Galactic Nuclei
• Mid-Infrared Selection of Active Galactic Nuclei with the Wide-Field Infrared Survey Explorer. II. Properties of WISE-Selected Active Galactic Nuclei in the NDWFS Boötes Field
• The dust covering factor in active galactic nuclei
• Using the Bright Ultra-Hard XMM-Newton Survey to define an IR selection of luminous AGN based on WISE colours
• The VIMOS Public Extragalactic Redshift Survey (VIPERS). An unprecedented view of galaxies and large-scale structure at 0.5<z<1.2
• The incidence of obscuration in active galactic nuclei
• The XXL Survey: I. Scientific motivations - XMM-Newton observing plan - Follow-up observations and simulation programme
• Constraining the properties of AGN host galaxies with Spectral Energy Distribution modeling
• The Chandra COSMOS Survey: III. Optical and Infrared Identification of X-ray Point Sources
• The WISE AGN Catalog
• The VIMOS Public Extragalactic Redshift Survey (VIPERS). Full spectroscopic data and auxiliary information release (PDR-2)
• Chasing highly obscured QSOs in the COSMOS field
• The VISTA Science Archive
• The dusty heart of nearby active galaxies -- II. From clumpy torus models to physical properties of dust around AGN
• Characterizing the Mid-IR Extragalactic Sky with WISE and SDSS
• The dusty heart of nearby active galaxies. I. High-spatial resolution mid-IR spectro-photometry of Seyfert galaxies
• Dusty winds in active galactic nuclei: reconciling observations with models
• A large population of mid-infrared selected, obscured active galaxies in the Bootes field
• XMM and Chandra measurements of the AGN intrinsic absorption: dependence on luminosity and redshift
• The Comptonisation of accretion disc X-ray emission: Consequences for X-ray reflection and the geometry of AGN coronae
• The Angular Clustering of WISE-Selected AGN: Different Haloes for Obscured and Unobscured AGN
• Probabilistic multi-catalogue positional cross-match
• Back to the Lithium Plateau with J0023+0307 with [Fe/H]<-6
• Disentangling the AGN and Star-Formation connection using XMM-Newton
• Composite Spectral Energy Distributions and Infrared-Optical Colors of Type 1 and Type 2 Quasars
• The XXL Survey: VI. The 1000 brightest X-ray point sources
• The XXL Survey: XXVII. The 3XLSS point source catalogue
• On R-W1 as A Diagnostic to Discover Obscured Active Galactic Nuclei in Wide-Area X-ray Surveys
• X-ray absorption in distant type II QSOs
• The relationship between X-ray and optical absorbers in active galactic nuclei
• XMMFITCAT: The XMM-Newton spectral-fit database
• Searching for luminous absorbed sources in the WISE AGN catalogue

Cited by in corpus (9)

• Galaxy properties of type 1 and 2 X-ray selected AGN and comparison among different classification criteria
• X-ray flux in the SED modelling: An application of X-CIGALE in the XMM-XXL field
• The relation between AGN type and host galaxy properties
• The role of AGN and its obscuration on the position of the host galaxy relative to Main Sequence
• AGN populations in the local universe: their alignment with the main-sequence, characteristics of their stellar populations, accretion efficiency, and the impact of AGN feedback
• XXL-HSC: Host properties of X-ray detected AGNs in XXL clusters
• The incidence of X-ray AGN and non-AGN galaxies in the far-infrared: insights into host galaxy properties and AGN obscuration
• AGN obscuration in optical and X-rays: Host properties and the interplay of nuclear and galactic gas and dust in a combined SDSS-XMM sample
• Nuclear Activity and Host Galaxy Properties of Low-Luminosity AGN Identified from VLA Observations