The origin of the cosmic soft X-ray background: Optical identification of an extremely deep ROSAT survey
We present the results of the deepest optically identified X-ray survey yet made. The X-ray survey was obtained with the ROSAT position-sensitive proportional counter (PSPC) and reaches a flux limit of 1.6 × 10-15 erg cm-2 s-1 (0.5-2.0 keV). Above a flux limit of 2 × 10-15 erg cm-2 s-1 we define a c...
| Autores: | , , , , , , , , , , , , , , , , , |
|---|---|
| Tipo de documento: | artigo |
| Estado: | Versão publicada |
| Data de publicação: | 1998 |
| País: | España |
| Recursos: | Consejo Superior de Investigaciones Científicas (CSIC) |
| Repositório: | DIGITAL.CSIC. Repositorio Institucional del CSIC |
| OAI Identifier: | oai:digital.csic.es:10261/170137 |
| Acesso em linha: | http://hdl.handle.net/10261/170137 |
| Access Level: | Acceso aberto |
| Palavra-chave: | Quasars: emission lines Diffuse radiation X-ray galaxies X-ray general Galaxies: clusters: general Galaxies: active |
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The origin of the cosmic soft X-ray background: Optical identification of an extremely deep ROSAT surveyMcHardy, I. M.Jones, L. R.Merrifield, M. R.Mason, Keith O.Newsam, A. M.Abraham, R. G.Dalton, G. B.Carrera, Francisco J.Smith, P. J.Rowan-Robinson, MichaelWegner, G. A.Ponman, T. J.Lehto, Harry J.Branduardi-Raymont, G.Luppino, G. A.Efstathiou, G.Allan, D. J.Quenby, J. J.Quasars: emission linesDiffuse radiationX-ray galaxiesX-ray generalGalaxies: clusters: generalGalaxies: activeWe present the results of the deepest optically identified X-ray survey yet made. The X-ray survey was obtained with the ROSAT position-sensitive proportional counter (PSPC) and reaches a flux limit of 1.6 × 10-15 erg cm-2 s-1 (0.5-2.0 keV). Above a flux limit of 2 × 10-15 erg cm-2 s-1 we define a complete sample of 70 sources, of which 59 are identified. For a further five sources we have tentative identifications and for a further four the X-ray error boxes are blank to R = 23 mag. At brighter fluxes (≥10-14 erg cm-2 s-1) we confirm the results of previous less deep X-ray surveys, with 84 per cent of our sources being QSOs. However, at the faint flux limit the survey is dominated by a population of galaxies with narrow emission lines (NELGs). In addition, at intermediate fluxes we find a small number of groups and clusters of galaxies at redshifts generally >0.3. Most of these groups are poor systems of low X-ray luminosity and the number that we find is consistent with a zero evolutionary scenario, unlike the situation for high-luminosity clusters at the same redshift. To a flux limit of 2 × 10-15 erg cm-2 s-1, QSOs contribute >31 percent of the cosmic soft X-ray background (XRB), groups/clusters contribute ∼10 per cent and NELGs contribute ∼8 per cent. However, the QSO differential source count slope below 10-14 erg cm-2 s-1 is ∼ -1.4, severely sub-Euclidean, as is the (poorly defined) group/cluster slope, whereas the differential NELG slope is close to Euclidean (∼ -2.4). If the NELG source counts continue to rise at that slope, all of the remaining cosmic soft XRB will be explained by a flux limit of ∼1-2 × 10-16 erg cm-2 s-1, with NELGs contributing about one quarter of the XRB. The average NELG X-ray spectrum is harder than that of the QSOs, and similar to that of the remaining unresolved cosmic XRB, suggesting that NELGs will also be substantial contributors to the XRB at higher energies. The observed NELGs lie in the redshift range 0.1-0.6 and have MR= -20 to -23, approximately 3 mag more luminous than typical field galaxies. They have predominantly blue colours, and some are definitely spirals, but the presence of some ellipticals cannot yet be ruled out. Many are in interacting or disturbed systems. The NELGs have optical spectra similar to those of the majority of the field galaxy population at a similar redshift and may simply be the more luminous members of the emission-line field galaxy population. Based on optical line ratios and X-ray/optical flux ratios, the NELGs, both as a sample and within individual galaxies, appear to be a mixture of starburst galaxies and true active galactic nuclei (AGN).This work was supported by grants to a number of authors from the UK Science and Engineering Research Council and Particle Physics and Astronomy Research Council. KOM acknowledges support from the Royal Society. FJC acknowledges partial financial support from the DGES under project PB95-0122.Peer ReviewedRoyal Astronomical SocietyOxford University PressResearch Councils UKRoyal Society (UK)Consejo Superior de Investigaciones Científicas [https://ror.org/02gfc7t72]2018201819982018info:eu-repo/semantics/articlehttp://purl.org/coar/resource_type/c_6501Publisher's versioninfo:eu-repo/semantics/publishedVersionhttp://hdl.handle.net/10261/170137reponame:DIGITAL.CSIC. Repositorio Institucional del CSICinstname:Consejo Superior de Investigaciones Científicas (CSIC)Ingléshttps://doi.org/10.1046/j.1365-8711.1998.01318.xSíinfo:eu-repo/semantics/openAccessoai:digital.csic.es:10261/1701372026-05-22T06:33:51Z |
| dc.title.none.fl_str_mv |
The origin of the cosmic soft X-ray background: Optical identification of an extremely deep ROSAT survey |
| title |
The origin of the cosmic soft X-ray background: Optical identification of an extremely deep ROSAT survey |
| spellingShingle |
The origin of the cosmic soft X-ray background: Optical identification of an extremely deep ROSAT survey McHardy, I. M. Quasars: emission lines Diffuse radiation X-ray galaxies X-ray general Galaxies: clusters: general Galaxies: active |
| title_short |
The origin of the cosmic soft X-ray background: Optical identification of an extremely deep ROSAT survey |
| title_full |
The origin of the cosmic soft X-ray background: Optical identification of an extremely deep ROSAT survey |
| title_fullStr |
The origin of the cosmic soft X-ray background: Optical identification of an extremely deep ROSAT survey |
| title_full_unstemmed |
The origin of the cosmic soft X-ray background: Optical identification of an extremely deep ROSAT survey |
| title_sort |
The origin of the cosmic soft X-ray background: Optical identification of an extremely deep ROSAT survey |
| dc.creator.none.fl_str_mv |
McHardy, I. M. Jones, L. R. Merrifield, M. R. Mason, Keith O. Newsam, A. M. Abraham, R. G. Dalton, G. B. Carrera, Francisco J. Smith, P. J. Rowan-Robinson, Michael Wegner, G. A. Ponman, T. J. Lehto, Harry J. Branduardi-Raymont, G. Luppino, G. A. Efstathiou, G. Allan, D. J. Quenby, J. J. |
| author |
McHardy, I. M. |
| author_facet |
McHardy, I. M. Jones, L. R. Merrifield, M. R. Mason, Keith O. Newsam, A. M. Abraham, R. G. Dalton, G. B. Carrera, Francisco J. Smith, P. J. Rowan-Robinson, Michael Wegner, G. A. Ponman, T. J. Lehto, Harry J. Branduardi-Raymont, G. Luppino, G. A. Efstathiou, G. Allan, D. J. Quenby, J. J. |
| author_role |
author |
| author2 |
Jones, L. R. Merrifield, M. R. Mason, Keith O. Newsam, A. M. Abraham, R. G. Dalton, G. B. Carrera, Francisco J. Smith, P. J. Rowan-Robinson, Michael Wegner, G. A. Ponman, T. J. Lehto, Harry J. Branduardi-Raymont, G. Luppino, G. A. Efstathiou, G. Allan, D. J. Quenby, J. J. |
| author2_role |
author author author author author author author author author author author author author author author author author |
| dc.contributor.none.fl_str_mv |
Research Councils UK Royal Society (UK) Consejo Superior de Investigaciones Científicas [https://ror.org/02gfc7t72] |
| dc.subject.none.fl_str_mv |
Quasars: emission lines Diffuse radiation X-ray galaxies X-ray general Galaxies: clusters: general Galaxies: active |
| topic |
Quasars: emission lines Diffuse radiation X-ray galaxies X-ray general Galaxies: clusters: general Galaxies: active |
| description |
We present the results of the deepest optically identified X-ray survey yet made. The X-ray survey was obtained with the ROSAT position-sensitive proportional counter (PSPC) and reaches a flux limit of 1.6 × 10-15 erg cm-2 s-1 (0.5-2.0 keV). Above a flux limit of 2 × 10-15 erg cm-2 s-1 we define a complete sample of 70 sources, of which 59 are identified. For a further five sources we have tentative identifications and for a further four the X-ray error boxes are blank to R = 23 mag. At brighter fluxes (≥10-14 erg cm-2 s-1) we confirm the results of previous less deep X-ray surveys, with 84 per cent of our sources being QSOs. However, at the faint flux limit the survey is dominated by a population of galaxies with narrow emission lines (NELGs). In addition, at intermediate fluxes we find a small number of groups and clusters of galaxies at redshifts generally >0.3. Most of these groups are poor systems of low X-ray luminosity and the number that we find is consistent with a zero evolutionary scenario, unlike the situation for high-luminosity clusters at the same redshift. To a flux limit of 2 × 10-15 erg cm-2 s-1, QSOs contribute >31 percent of the cosmic soft X-ray background (XRB), groups/clusters contribute ∼10 per cent and NELGs contribute ∼8 per cent. However, the QSO differential source count slope below 10-14 erg cm-2 s-1 is ∼ -1.4, severely sub-Euclidean, as is the (poorly defined) group/cluster slope, whereas the differential NELG slope is close to Euclidean (∼ -2.4). If the NELG source counts continue to rise at that slope, all of the remaining cosmic soft XRB will be explained by a flux limit of ∼1-2 × 10-16 erg cm-2 s-1, with NELGs contributing about one quarter of the XRB. The average NELG X-ray spectrum is harder than that of the QSOs, and similar to that of the remaining unresolved cosmic XRB, suggesting that NELGs will also be substantial contributors to the XRB at higher energies. The observed NELGs lie in the redshift range 0.1-0.6 and have MR= -20 to -23, approximately 3 mag more luminous than typical field galaxies. They have predominantly blue colours, and some are definitely spirals, but the presence of some ellipticals cannot yet be ruled out. Many are in interacting or disturbed systems. The NELGs have optical spectra similar to those of the majority of the field galaxy population at a similar redshift and may simply be the more luminous members of the emission-line field galaxy population. Based on optical line ratios and X-ray/optical flux ratios, the NELGs, both as a sample and within individual galaxies, appear to be a mixture of starburst galaxies and true active galactic nuclei (AGN). |
| publishDate |
1998 |
| dc.date.none.fl_str_mv |
1998 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 |
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article |
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publishedVersion |
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http://hdl.handle.net/10261/170137 |
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http://hdl.handle.net/10261/170137 |
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Inglés |
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Inglés |
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https://doi.org/10.1046/j.1365-8711.1998.01318.x Sí |
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info:eu-repo/semantics/openAccess |
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openAccess |
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Royal Astronomical Society Oxford University Press |
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Royal Astronomical Society Oxford University Press |
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DIGITAL.CSIC. Repositorio Institucional del CSIC |
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