Obscuration properties of mid-IR-selected AGN

Mountrichas, G.; Georgantopoulos, I.; Ruiz, Ángel Liceras; Kampylis, G.

doi:10.1093/mnras/stz3076

Cited by 12 publications

(11 citation statements)

References 48 publications

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“…Our analysis of XMMFITCAT-Z sources is consistent with many previous studies (Eckart et al 2010;Stern et al 2012;Assef et al 2013;Yan et al 2013;Mateos et al 2012Mateos et al , 2013Mountrichas et al 2017bMountrichas et al , 2020Pouliasis et al 2020) showing that MIR diagnostics are powerful for the identification of luminous AGN, but they fail for AGN with lower luminosity and/or mild absorption, where the stellar contribution to the optical/MIR emission is non-negligible. By focusing on the X-ray properties, we can identify these objects.…”

Section: Discussionsupporting

confidence: 91%

A search for X-ray absorbed sources in the 3XMM catalogue using photometric redshifts and Bayesian spectral fits

Ruiz

Georgantopoulos

Corral

2021

A&A

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Since its launch in 1999, the XMM-Newton mission has compiled the largest catalogue of serendipitous X-ray sources, with the 3XMM being the third version of this catalogue. This was possible thanks to the combination of a large effective area (5000 cm 2 at 1 keV) and a wide field of view (30 arcmin). The 3XMM-DR6 catalogue contains about 470 000 unique X-ray sources over an area of 982 deg 2. A significant fraction of these (100 178 sources) have reliable optical, near-(NIR), and mid-infrared (MIR) counterparts in the SDSS, PANSTARRS, VIDEO, UKIDSS, and WISE surveys. In a previous paper we presented photometric redshifts for these sources using the TPZ machine-learning algorithm. About a quarter of these (22 677) have adequate photon statistics, meaning that a reliable X-ray spectrum can be extracted. Owing to both the X-ray counts selection and the optical counterpart constraint, the sample above is biased towards the bright sources. Here, we present XMMFITCAT-Z: a spectral fit catalogue for these sources using the Bayesian X-ray Analysis (BXA) technique. To demonstrate the potential of the present catalogue, we comment on the optical and MIR colours of the 765 X-ray absorbed sources with N H > 10 22 cm −2. We show that a considerable fraction of X-ray-selected AGNs would not be classified as AGNs following the MIR W1-W2 versus W2 selection criterion. These are AGNs with lower luminosities, where the contribution of the host galaxy to the MIR emission is non-negligible. Only one-third of obscured AGNs in X-rays present red colours or r-W2 > 6. Also, it appears that the r-W2 criterion, often used in the literature for the selection of obscured AGNs, produces very different X-ray absorbed AGN samples compared to the standard X-ray selection criteria.

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Section: Discussionsupporting

confidence: 91%

A search for X-ray absorbed sources in the 3XMM catalogue using photometric redshifts and Bayesian spectral fits

Ruiz

Georgantopoulos

Corral

2021

A&A

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“…Although these colour criteria are very efficient in uncovering obscured AGN selected in the mid-IR, X-rays are known to miss a large fraction of obscured sources selected based on optical-IR colours. Mountrichas et al (2020) used sources detected in Stripe 82 and found that among IR selected AGN with an SDSS detection, 43% are optically red. However, this percentage drops to 23% among those AGN that are also X-ray detected.…”

Section: Effectiveness Of Optical / Mid-ir Colours In Classifying X-r...mentioning

confidence: 99%

Galaxy properties of type 1 and 2 X-ray selected AGN and a comparison among different classification criteria

Mountrichas

Buat

Georgantopoulos

et al. 2021

A&A

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We present analyses of host galaxy properties of type 1 and type 2 X-ray selected Active galactic nuclei (AGNs) in the XMM-XXL field, which have an available optical spectroscopic classification. We modelled their optical to far-infrared spectral energy distributions (SEDs) using the X-CIGALE code. X-CIGALE allows for the fitting of X-ray flux and accounts for the viewing angle of dusty torus and the attenuation from polar dust. By selecting matched type 1 and 2 sub-samples in the X-ray luminosity and redshift parameter space, we find that both types live in galaxies with similar star formation. However, type 2 AGN tend to reside in more massive systems (10.87−0.12+0.06 M⊙) compared to their type 1 counterparts (10.57−0.12+0.20 M⊙). In the second part of our analysis, we compare the spectroscopic classification with that from the SED fitting. X-CIGALE successfully identifies all spectroscopic type 2 sources either by estimating an inclination angle that corresponds to edge on viewing of the source or by measuring increased polar dust in these systems. Approximately 85% of spectroscopic type 1 AGN are also identified as such, based on the SED fitting analysis. There is a small number of sources (∼15% of the sample) that present broad lines in their spectra, but they show strong indications of obscuration, based on SED analysis. These could be systems that are viewed face on and have an extended dust component along the polar direction. The performance of X-CIGALE in classifying AGN is similar at low and high redshifts, under the condition that there is sufficient photometric coverage. Finally, the usage of optical/mid-IR colour criteria to identify optical red AGN (u − W3) suggests that these criteria are better suited for IR selected AGN and their efficiency drops for the low to moderate luminosity sources included in X-ray samples.

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“…Although these colour criteria are very efficient in uncovering obscured AGN selected in the mid-IR, X-rays are known to miss a large fraction of obscured sources selected based on optical/mid-IR colours. Mountrichas et al (2020) used sources detected in Stripe 82 and found that among IR selected AGN with SDSS detection, 43% are optically red. However, this percentage drops to 23% among those AGN that are also X-ray detected.…”

Section: Effectiveness Of Optical / Mid-ir Colours In Classifying X-r...mentioning

confidence: 99%

Galaxy properties of type 1 and 2 X-ray selected AGN and comparison among different classification criteria

Mountrichas,

Buat,

Georgantopoulos

et al. 2021

Preprint

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We present analyses of host galaxy properties of type 1 and type 2 X-ray selected AGNs in the XMM-XXL field, which have available optical spectroscopic classification. We model their optical to far-infrared spectral energy distributions (SEDs) using the X-CIGALE code. X-CIGALE allows the fitting of X-ray flux and accounts for the viewing angle of dusty torus and the attenuation from polar dust. By selecting matched type 1 and 2 subsamples in the X-ray luminosity and redshift parameter space, we find that both types live in galaxies with similar star formation. However, type 2 AGN tend to reside in more massive systems (10.87 +0.06 −0.12 M ) compared to their type 1 counterparts (10.57 +0.20 −0.12 M ). In the second part of our analysis, we compare the spectroscopic classification with that from the SED fitting. X-CIGALE successfully identifies all spectroscopic type 2 sources either by estimating an inclination angle that corresponds to edge on viewing of the source or by measuring increased polar dust in these systems. ∼ 85% of spectroscopic type 1 AGN are also identified as such, based on the SED fitting analysis. There is a small number of sources (∼ 15% of the sample), that present broad lines in their spectra, but show strong indications of obscuration, based on SED analysis. These, could be systems that are viewed face on and have an extended dust component along the polar direction. The performance of X-CIGALE in classifying AGN is similar at low and high redshifts, under the condition that there is sufficient photometric coverage. Finally, usage of optical/mid-IR colour criteria to identify optical red AGN (u − W3), suggests that these criteria are better suited for IR selected AGN and their efficiency drops for the low to moderate luminosity sources included in X-ray samples.

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Obscuration properties of mid-IR-selected AGN

Cited by 12 publications

References 48 publications

A search for X-ray absorbed sources in the 3XMM catalogue using photometric redshifts and Bayesian spectral fits

A search for X-ray absorbed sources in the 3XMM catalogue using photometric redshifts and Bayesian spectral fits

Galaxy properties of type 1 and 2 X-ray selected AGN and a comparison among different classification criteria

Galaxy properties of type 1 and 2 X-ray selected AGN and comparison among different classification criteria

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