Elusive AGN in the XMM-Newton bright serendipitous survey

[Context]: Optical follow up of X-ray selected sources finds a significant fraction ot >optically dull> sources characterized by optical spectra without obvious signature of AGN activity. In many cases, however, the presence of an AGN is inferred from other diagnostics (e.g. the X-ray properti...

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Detalles Bibliográficos
Autores: Caccianiga, A., Severgnini, P., Della Ceca, R., Maccacaro, T., Carrera, Francisco J., Page, Matt
Tipo de recurso: artículo
Estado:Versión publicada
Fecha de publicación:2007
País:España
Institución:Consejo Superior de Investigaciones Científicas (CSIC)
Repositorio:DIGITAL.CSIC. Repositorio Institucional del CSIC
OAI Identifier:oai:digital.csic.es:10261/169675
Acceso en línea:http://hdl.handle.net/10261/169675
Access Level:acceso abierto
Palabra clave:Surveys
X-ray: galaxies
Galaxies: nuclei
Galaxies: active
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spelling Elusive AGN in the XMM-Newton bright serendipitous surveyCaccianiga, A.Severgnini, P.Della Ceca, R.Maccacaro, T.Carrera, Francisco J.Page, MattSurveysX-ray: galaxiesGalaxies: nucleiGalaxies: active[Context]: Optical follow up of X-ray selected sources finds a significant fraction ot >optically dull> sources characterized by optical spectra without obvious signature of AGN activity. In many cases, however, the presence of an AGN is inferred from other diagnostics (e.g. the X-ray properties). Understanding and accounting for this >elusiveness> is mandatory for a reliable study of the AGN physical and statistical properties. [Aims]: We investigate here the nature of all the sources (35 in total) in the XMM-Newton bright serendipitous survey (which is 86% optically identified) showing an optical spectrum dominated by the light from the host galaxy with no evidence (or little evidence) for the presence of an AGN. [Methods]: We use the X-ray spectral analysis to assess the presence of an AGN in these sources and to characterize its properties. [Results]: We detect AGN activity in 33 out of 35 sources. The remaining 2 sources are the ones with the lowest X-ray luminosity in the sample (L[2-10 keV] < 1041 erg s-1) and their X-ray emission could be produced within the host galaxy. We find that the >recognition problem> for AGN is very critical in the low-luminosity regime (at least 60% of the AGN with L[2-10 keV] < 1043 erg s-1 are elusive) becoming negligible for high X-ray luminosities (∼1.5% of elusive AGN with L[2-10 keV] > 1044 erg s-1). This problem affects mostly absorbed AGN (∼40% of type 2 AGN in the survey are elusive) but also a significant fraction of unabsorbed AGN (8%). [Conclusions]: We find that the simplest explanations of why these 33 (or most of them) AGNs are elusive are two: at low X-ray luminosities (<1043 erg s-1) the most important reason is the intrinsically low AGN/galaxy contrast (optical dilution) while at high luminosities (>1044 erg s-1) it is due to the optical absorption (in the Compton-thin regime, i.e. NH < 10 24 cm-2). Alternative hypotheses, like the presence of Compton-thick sources, BL Lac objects or >non-standard> AGN (e.g. with αOX < 1 or with weak/absorbed Narrow Line Region) are not supported by the data although we cannot exclude the presence in the sample of a few sources of these types.Peer ReviewedEDP SciencesConsejo Superior de Investigaciones Científicas [https://ror.org/02gfc7t72]2018201820072018info:eu-repo/semantics/articlehttp://purl.org/coar/resource_type/c_6501Publisher's versioninfo:eu-repo/semantics/publishedVersionhttp://hdl.handle.net/10261/169675reponame:DIGITAL.CSIC. Repositorio Institucional del CSICinstname:Consejo Superior de Investigaciones Científicas (CSIC)Ingléshttps://doi.org/10.1051/0004-6361:20077732Síinfo:eu-repo/semantics/openAccessoai:digital.csic.es:10261/1696752026-05-22T06:33:51Z
dc.title.none.fl_str_mv Elusive AGN in the XMM-Newton bright serendipitous survey
title Elusive AGN in the XMM-Newton bright serendipitous survey
spellingShingle Elusive AGN in the XMM-Newton bright serendipitous survey
Caccianiga, A.
Surveys
X-ray: galaxies
Galaxies: nuclei
Galaxies: active
title_short Elusive AGN in the XMM-Newton bright serendipitous survey
title_full Elusive AGN in the XMM-Newton bright serendipitous survey
title_fullStr Elusive AGN in the XMM-Newton bright serendipitous survey
title_full_unstemmed Elusive AGN in the XMM-Newton bright serendipitous survey
title_sort Elusive AGN in the XMM-Newton bright serendipitous survey
dc.creator.none.fl_str_mv Caccianiga, A.
Severgnini, P.
Della Ceca, R.
Maccacaro, T.
Carrera, Francisco J.
Page, Matt
author Caccianiga, A.
author_facet Caccianiga, A.
Severgnini, P.
Della Ceca, R.
Maccacaro, T.
Carrera, Francisco J.
Page, Matt
author_role author
author2 Severgnini, P.
Della Ceca, R.
Maccacaro, T.
Carrera, Francisco J.
Page, Matt
author2_role author
author
author
author
author
dc.contributor.none.fl_str_mv Consejo Superior de Investigaciones Científicas [https://ror.org/02gfc7t72]
dc.subject.none.fl_str_mv Surveys
X-ray: galaxies
Galaxies: nuclei
Galaxies: active
topic Surveys
X-ray: galaxies
Galaxies: nuclei
Galaxies: active
description [Context]: Optical follow up of X-ray selected sources finds a significant fraction ot >optically dull> sources characterized by optical spectra without obvious signature of AGN activity. In many cases, however, the presence of an AGN is inferred from other diagnostics (e.g. the X-ray properties). Understanding and accounting for this >elusiveness> is mandatory for a reliable study of the AGN physical and statistical properties. [Aims]: We investigate here the nature of all the sources (35 in total) in the XMM-Newton bright serendipitous survey (which is 86% optically identified) showing an optical spectrum dominated by the light from the host galaxy with no evidence (or little evidence) for the presence of an AGN. [Methods]: We use the X-ray spectral analysis to assess the presence of an AGN in these sources and to characterize its properties. [Results]: We detect AGN activity in 33 out of 35 sources. The remaining 2 sources are the ones with the lowest X-ray luminosity in the sample (L[2-10 keV] < 1041 erg s-1) and their X-ray emission could be produced within the host galaxy. We find that the >recognition problem> for AGN is very critical in the low-luminosity regime (at least 60% of the AGN with L[2-10 keV] < 1043 erg s-1 are elusive) becoming negligible for high X-ray luminosities (∼1.5% of elusive AGN with L[2-10 keV] > 1044 erg s-1). This problem affects mostly absorbed AGN (∼40% of type 2 AGN in the survey are elusive) but also a significant fraction of unabsorbed AGN (8%). [Conclusions]: We find that the simplest explanations of why these 33 (or most of them) AGNs are elusive are two: at low X-ray luminosities (<1043 erg s-1) the most important reason is the intrinsically low AGN/galaxy contrast (optical dilution) while at high luminosities (>1044 erg s-1) it is due to the optical absorption (in the Compton-thin regime, i.e. NH < 10 24 cm-2). Alternative hypotheses, like the presence of Compton-thick sources, BL Lac objects or >non-standard> AGN (e.g. with αOX < 1 or with weak/absorbed Narrow Line Region) are not supported by the data although we cannot exclude the presence in the sample of a few sources of these types.
publishDate 2007
dc.date.none.fl_str_mv 2007
2018
2018
2018
dc.type.none.fl_str_mv info:eu-repo/semantics/article
http://purl.org/coar/resource_type/c_6501
Publisher's version
info:eu-repo/semantics/publishedVersion
format article
status_str publishedVersion
dc.identifier.none.fl_str_mv http://hdl.handle.net/10261/169675
url http://hdl.handle.net/10261/169675
dc.language.none.fl_str_mv Inglés
language_invalid_str_mv Inglés
dc.relation.none.fl_str_mv https://doi.org/10.1051/0004-6361:20077732
Sí
dc.rights.none.fl_str_mv info:eu-repo/semantics/openAccess
eu_rights_str_mv openAccess
dc.publisher.none.fl_str_mv EDP Sciences
publisher.none.fl_str_mv EDP Sciences
dc.source.none.fl_str_mv reponame:DIGITAL.CSIC. Repositorio Institucional del CSIC
instname:Consejo Superior de Investigaciones Científicas (CSIC)
instname_str Consejo Superior de Investigaciones Científicas (CSIC)
reponame_str DIGITAL.CSIC. Repositorio Institucional del CSIC
collection DIGITAL.CSIC. Repositorio Institucional del CSIC
repository.name.fl_str_mv
repository.mail.fl_str_mv
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score 15.81155

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