A new technique to efficiently select Compton-thick AGN

Severgnini, P.; Caccianiga, A.; Ceca, R. Della

doi:10.1051/0004-6361/201118417

Cited by 48 publications

(61 citation statements)

References 59 publications

(116 reference statements)

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“…A broad Hα component has also been tentatively detected in total flux (Young et al 1996). As mentioned before, IRAS 15480 is a CT object, with an N H > 1 × 10 24 cm −2 (Severgnini et al 2012;Brightman & Nandra 2011;Guainazzi et al 2005). The detection of a silicate absorption feature in the Spitzer IR spectrum of IRAS 15480 is consistent with the presence of an obscuring torus viewed nearly edge-on (Gallimore et al 2010).…”

Section: The Compton-thick Seyfert Galaxy Iras 15480supporting

confidence: 66%

“…As part of a search for water maser emission in a well defined sample of Compton-thick (CT) AGN (Severgnini et al 2012), we detected a luminous H 2 O maser in the mid-IR-bright Seyfert 2 galaxy IRAS 15480-0344 (hereafter IRAS 15480). The results of the entire survey and their statistical analysis will be reported in a forthcoming paper (Paper II, in prep.).…”

Section: Introductionmentioning

confidence: 99%

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Water masers in Compton-thick AGN

Castangia¹,

Tarchi²,

Caccianiga³

et al. 2016

A&A

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Context.A relationship between the water maser detection rate and large nuclear column densities in AGN has often been cited in the literature. Indeed, detailed studies of luminous water masers, typically associated with the nuclear activity, allow us to investigate the innermost regions of AGN, with an impact on the still debated Unified Model for this class of objects. Aims. We have recently entertained a search for maser emission in a well-defined sample of Compton-thick AGN aimed at investigating, on firm statistical bases, the aforementioned relationship. While the survey is still ongoing, and is the subject of a forthcoming publication, a new luminous water maser has been detected in the lenticular (field) S0 galaxy IRAS 15480-0344, whose origin, associated with an accretion disc or a nuclear outflow/jet, needs to be assessed. Methods. Multi-epoch single-dish observations and VLBI measurements were performed to investigate the distribution, spatial extension, and variability of the maser emission in order to infer the main characteristics of the water megamaser. Results. The new detection in IRAS 15480-0344 is reported: a megamaser with a total single-dish isotropic luminosity of ∼200 L and a profile composed of two main features, a broad line with a full width to half maximum (FWHM) linewidth of ∼90 km s −1 and a narrow (FWHM < 1 km s −1 ) one. We performed a follow-up to the detection with the Very Long Baseline Array (VLBA) and confidently detected only the narrow component, which is coincident with the nuclear radio continuum emission detected with the Very Large Array at 8.4 GHz. A weak narrow feature has also been detected in the velocity range of the broad feature and is located 15 pc to the north-west with respect to the stronger component. Neither maser spot is associated with the compact radio continuum sources derived from the same VLBA dataset. Conclusions. The different line profiles and the spatial separation between the two features in the spectrum of IRAS 15480-0344 suggests a composite origin for the maser. The large linewidth and the strong spectral variability indicate that the broad component might originate from the interaction between a radio jet and ambient molecular clouds. Based on its small linewidth and the absence of high velocity features, instead, we favour an outflow origin for the narrow component. This scenario is consistent with the hypothesis of the presence of strong nuclear outflows recently invoked to explain the main characteristics of field S0 galaxies.

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Section: The Compton-thick Seyfert Galaxy Iras 15480supporting

confidence: 66%

Section: Introductionmentioning

confidence: 99%

Water masers in Compton-thick AGN

Castangia¹,

Tarchi²,

Caccianiga³

et al. 2016

A&A

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“…A pointlike source is observed in hard X-rays, while extended emission can be observed in soft X-rays, aligned with the bars (see Appendix C.1). It was classified as a Compton-thick candidate (Guainazzi et al 2005b;Bianchi et al 2010;Severgnini et al 2012).…”

Section: Appendix B: Notes and Comparisons With Previous Results For mentioning

confidence: 99%

X-ray spectral variability of Seyfert 2 galaxies

Hernández-García

Masegosa

González‐Martín³

et al. 2015

A&A

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Context. Variability across the electromagnetic spectrum is a property of active galactic nuclei (AGN) that can help constrain the physical properties of these galaxies. Nonetheless, the way in which the changes happen and whether they occur in the same way in every AGN are still open questions. Aims. This is the third in a series of papers with the aim of studying the X-ray variability of different families of AGN. The main purpose of this work is to investigate the variability pattern(s) in a sample of optically selected Seyfert 2 galaxies. Methods. We use the 26 Seyfert 2s in the Véron-Cetty and Véron catalog with data available from Chandra and/or XMM-Newton public archives at different epochs, with timescales ranging from a few hours to years. All the spectra of the same source were simultaneously fitted, and we let different parameters vary in the model. Whenever possible, short-term variations from the analysis of the light curves and/or long-term UV flux variations were studied. We divided the sample into Compton-thick and Compton-thin candidates to account for the degree of obscuration. When transitions between Compton-thick and thin were obtained for different observations of the same source, we classified it as a changing-look candidate. Results. Short-term variability at X-rays was studied in ten cases, but variations are not found. From the 25 analyzed sources, 11 show long-term variations. Eight (out of 11) are Compton-thin, one (out of 12) is Compton-thick, and the two changing-look candidates are also variable. The main driver for the X-ray changes is related to the nuclear power (nine cases), while variations at soft energies or related to absorbers at hard X-rays are less common, and in many cases these variations are accompanied by variations in the nuclear continuum. At UV frequencies, only NGC 5194 (out of six sources) is variable, but the changes are not related to the nucleus. We report two changing-look candidates, MARK 273 and NGC 7319. Conclusions. A constant reflection component located far away from the nucleus plus a variable nuclear continuum are able to explain most of our results. Within this scenario, the Compton-thick candidates are dominated by reflection, which suppresses their continuum, making them seem fainter, and they do not show variations (except MARK 3), while the Compton-thin and changing-look candidates do.

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“…Waste heat in the mid-infrared (MIR) band of AGN is an efficient tool to find deeply buried AGN (e.g., Daddi et al 2007;Fiore et al 2008Fiore et al , 2009Gandhi et al 2009;Georgantopoulos et al 2009;Severgnini et al 2012;Asmus et al 2015;Stern 2015;Corral et al 2016;Isobe et al 2016). We cross-correlate our sample with the GOODS-Herschel catalog (Elbaz et al 2011) with a maximum separation of 1″, and find 167 MIR counterparts.…”

Section: Mid-infrared 12μm Luminositymentioning

confidence: 99%

X-Ray Spectral Analyses of AGNs from the 7Ms Chandra Deep Field-South Survey: The Distribution, Variability, and Evolutions of AGN Obscuration

Liu

Tozzi²,

Wang

et al. 2017

ApJS

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We present a detailed spectral analysis of the brightest active galactic nuclei (AGNs) identified in the 7Ms Chandra Deep Field-South (CDF-S) survey over a time span of 16 years. Using a model of an intrinsically absorbed power-law plus reflection, with possible soft excess and narrow Fe Kα line, we perform a systematic X-ray spectral analysis, both on the total 7Ms exposure and in four different periods with lengths of 2–21 months. With this approach, we not only present the power-law slopes, column densities , observed fluxes, and absorption-corrected 2–10 keV luminosities L X for our sample of AGNs, but also identify significant spectral variabilities among them on timescales of years. We find that the variabilities can be ascribed to two different types of mechanisms, either flux-driven or flux-independent. We also find that the correlation between the narrow Fe line EW and can be well explained by the continuum suppression with increasing . Accounting for the sample incompleteness and bias, we measure the intrinsic distribution of for the CDF-S AGN population and present reselected subsamples that are complete with respect to . The -complete subsamples enable us to decouple the dependences of on L X and on redshift. Combining our data with those from C-COSMOS, we confirm the anticorrelation between the average and L X of AGN, and find a significant increase of the AGN-obscured fraction with redshift at any luminosity. The obscured fraction can be described as .

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A new technique to efficiently select Compton-thick AGN

Cited by 48 publications

References 59 publications

Water masers in Compton-thick AGN

Water masers in Compton-thick AGN

X-ray spectral variability of Seyfert 2 galaxies

X-Ray Spectral Analyses of AGNs from the 7Ms Chandra Deep Field-South Survey: The Distribution, Variability, and Evolutions of AGN Obscuration

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