The stellar populations of low-luminosity active galactic nuclei. I. Ground-based observations
Autor(a) principal: | |
---|---|
Data de Publicação: | 2004 |
Outros Autores: | , , , , , , , |
Tipo de documento: | Artigo |
Idioma: | eng |
Título da fonte: | Repositório Institucional da UFRGS |
Texto Completo: | http://hdl.handle.net/10183/108913 |
Resumo: | We present a spectroscopic study of the stellar populations of low-luminosity active galactic nuclei (LLAGNs). Our main goal is to determine whether the stars that live in the innermost (100 pc scale) regions of these galaxies are in some way related to the emission-line properties, which would imply a link between the stellar population and the ionization mechanism. High signal-to-noise ratio, ground-based long-slit spectra in the 3500– 5500 Å interval were collected for 60 galaxies: 51 LINERs and LINER/H II transition objects, two starburst galaxies, and seven nonactive galaxies. In this paper, the first of a series, we (1) describe the sample; (2) present the nuclear spectra; (3) characterize the stellar populations of LLAGNs by means of an empirical comparison with normal galaxies; (4) measure a set of spectral indices, including several absorption-line equivalent widths and colors indicative of stellar populations; and (5) correlate the stellar indices with emission-line ratios that may distinguish between possible excitation sources for the gas. Our main findings are as follows: (1) Few LLAGNs have a detectable young (~<10 7 yr) starburst component, indicating that very massive stars do not contribute significantly to the optical continuum. In particular, no features due to Wolf-Rayet stars were convincingly detected. (2) High-order Balmer absorption lines of HI (HOBLs), on the other hand, are detected in ~40% of LLAGNs. These features, which are strongest in 10 8–10 9 yr intermediate-age stellar populations, are accompanied by diluted metal absorption lines and bluer colors than other objects in the sample. (3) These intermediateage populations are very common (~50%) in LLAGNs with relatively weak [O I] emission ([O I/Hα ≤ 0.25) but rare (~10%) in LLAGNs with stronger [O I]. This is intriguing since LLAGNs with weak [O I] have been previously hypothesized to be ‘‘transition objects’’ in which both an AGN and young stars contribute to the emission-line excitation. Massive stars, if present, are completely outshone by intermediate-age and old stars in the optical. This happens in at least a couple of objects where independent UV spectroscopy detects young starbursts not seen in the optical. (4) Objects with predominantly old stars span the whole range of [O I]/Hα values, but (5) sources with significant young and/or intermediate-age populations are nearly all (~90%) weak– [O I] emitters. These new findings suggest a link between the stellar populations and the gas ionization mechanism. The strong–[O I] objects are most likely true LLAGNs, with stellar processes being insignificant. However, the weak–[O I] objects may comprise two populations, one where the ionization is dominated by stellar processes and another where it is governed by either an AGN or a more even mixture of stellar and AGN processes. Possible stellar sources for the ionization include weak starbursts, supernova remnants, and evolved poststarburst populations. These scenarios are examined and constrained by means of complementary observations and detailed modeling of the stellar populations in forthcoming communications. |
id |
UFRGS-2_9ce91d5c4fc2fd2e57d2a07199cc92c7 |
---|---|
oai_identifier_str |
oai:www.lume.ufrgs.br:10183/108913 |
network_acronym_str |
UFRGS-2 |
network_name_str |
Repositório Institucional da UFRGS |
repository_id_str |
|
spelling |
Fernandes, Roberto CidGonzález Delgado, Rosa M.Schmitt, Henrique RobertoStorchi-Bergmann, ThaisaMartins, Lucimara PiresPérez Jiménez, EnriqueHeckman, Timothy M.Leitherer, ClausSchaerer, Daniel2015-01-14T02:15:56Z20040004-637Xhttp://hdl.handle.net/10183/108913000503985We present a spectroscopic study of the stellar populations of low-luminosity active galactic nuclei (LLAGNs). Our main goal is to determine whether the stars that live in the innermost (100 pc scale) regions of these galaxies are in some way related to the emission-line properties, which would imply a link between the stellar population and the ionization mechanism. High signal-to-noise ratio, ground-based long-slit spectra in the 3500– 5500 Å interval were collected for 60 galaxies: 51 LINERs and LINER/H II transition objects, two starburst galaxies, and seven nonactive galaxies. In this paper, the first of a series, we (1) describe the sample; (2) present the nuclear spectra; (3) characterize the stellar populations of LLAGNs by means of an empirical comparison with normal galaxies; (4) measure a set of spectral indices, including several absorption-line equivalent widths and colors indicative of stellar populations; and (5) correlate the stellar indices with emission-line ratios that may distinguish between possible excitation sources for the gas. Our main findings are as follows: (1) Few LLAGNs have a detectable young (~<10 7 yr) starburst component, indicating that very massive stars do not contribute significantly to the optical continuum. In particular, no features due to Wolf-Rayet stars were convincingly detected. (2) High-order Balmer absorption lines of HI (HOBLs), on the other hand, are detected in ~40% of LLAGNs. These features, which are strongest in 10 8–10 9 yr intermediate-age stellar populations, are accompanied by diluted metal absorption lines and bluer colors than other objects in the sample. (3) These intermediateage populations are very common (~50%) in LLAGNs with relatively weak [O I] emission ([O I/Hα ≤ 0.25) but rare (~10%) in LLAGNs with stronger [O I]. This is intriguing since LLAGNs with weak [O I] have been previously hypothesized to be ‘‘transition objects’’ in which both an AGN and young stars contribute to the emission-line excitation. Massive stars, if present, are completely outshone by intermediate-age and old stars in the optical. This happens in at least a couple of objects where independent UV spectroscopy detects young starbursts not seen in the optical. (4) Objects with predominantly old stars span the whole range of [O I]/Hα values, but (5) sources with significant young and/or intermediate-age populations are nearly all (~90%) weak– [O I] emitters. These new findings suggest a link between the stellar populations and the gas ionization mechanism. The strong–[O I] objects are most likely true LLAGNs, with stellar processes being insignificant. However, the weak–[O I] objects may comprise two populations, one where the ionization is dominated by stellar processes and another where it is governed by either an AGN or a more even mixture of stellar and AGN processes. Possible stellar sources for the ionization include weak starbursts, supernova remnants, and evolved poststarburst populations. These scenarios are examined and constrained by means of complementary observations and detailed modeling of the stellar populations in forthcoming communications.application/pdfengThe astrophysical journal. Chicago. Vol. 605, no. 1, pt. 1 (Apr. 2004), p. 105-126Galáxias ativasFotometria astronômicaNucleo galaticoEspectros astronômicosGalaxies: activeGalaxies: nucleiGalaxies: starburstGalaxies: stellar contentThe stellar populations of low-luminosity active galactic nuclei. I. Ground-based observationsEstrangeiroinfo:eu-repo/semantics/articleinfo:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/openAccessreponame:Repositório Institucional da UFRGSinstname:Universidade Federal do Rio Grande do Sul (UFRGS)instacron:UFRGSORIGINAL000503985.pdf000503985.pdfTexto completo (inglês)application/pdf1117563http://www.lume.ufrgs.br/bitstream/10183/108913/1/000503985.pdf968ffa7c5d04b986c925a5ac47db15d9MD51TEXT000503985.pdf.txt000503985.pdf.txtExtracted Texttext/plain103920http://www.lume.ufrgs.br/bitstream/10183/108913/2/000503985.pdf.txtfd72d1d779e6b07255fade0910e81a53MD52THUMBNAIL000503985.pdf.jpg000503985.pdf.jpgGenerated Thumbnailimage/jpeg1906http://www.lume.ufrgs.br/bitstream/10183/108913/3/000503985.pdf.jpg1fb66dd6291e9053e8c36cd1dfba4e89MD5310183/1089132018-10-23 08:40:15.341oai:www.lume.ufrgs.br:10183/108913Repositório de PublicaçõesPUBhttps://lume.ufrgs.br/oai/requestopendoar:2018-10-23T11:40:15Repositório Institucional da UFRGS - Universidade Federal do Rio Grande do Sul (UFRGS)false |
dc.title.pt_BR.fl_str_mv |
The stellar populations of low-luminosity active galactic nuclei. I. Ground-based observations |
title |
The stellar populations of low-luminosity active galactic nuclei. I. Ground-based observations |
spellingShingle |
The stellar populations of low-luminosity active galactic nuclei. I. Ground-based observations Fernandes, Roberto Cid Galáxias ativas Fotometria astronômica Nucleo galatico Espectros astronômicos Galaxies: active Galaxies: nuclei Galaxies: starburst Galaxies: stellar content |
title_short |
The stellar populations of low-luminosity active galactic nuclei. I. Ground-based observations |
title_full |
The stellar populations of low-luminosity active galactic nuclei. I. Ground-based observations |
title_fullStr |
The stellar populations of low-luminosity active galactic nuclei. I. Ground-based observations |
title_full_unstemmed |
The stellar populations of low-luminosity active galactic nuclei. I. Ground-based observations |
title_sort |
The stellar populations of low-luminosity active galactic nuclei. I. Ground-based observations |
author |
Fernandes, Roberto Cid |
author_facet |
Fernandes, Roberto Cid González Delgado, Rosa M. Schmitt, Henrique Roberto Storchi-Bergmann, Thaisa Martins, Lucimara Pires Pérez Jiménez, Enrique Heckman, Timothy M. Leitherer, Claus Schaerer, Daniel |
author_role |
author |
author2 |
González Delgado, Rosa M. Schmitt, Henrique Roberto Storchi-Bergmann, Thaisa Martins, Lucimara Pires Pérez Jiménez, Enrique Heckman, Timothy M. Leitherer, Claus Schaerer, Daniel |
author2_role |
author author author author author author author author |
dc.contributor.author.fl_str_mv |
Fernandes, Roberto Cid González Delgado, Rosa M. Schmitt, Henrique Roberto Storchi-Bergmann, Thaisa Martins, Lucimara Pires Pérez Jiménez, Enrique Heckman, Timothy M. Leitherer, Claus Schaerer, Daniel |
dc.subject.por.fl_str_mv |
Galáxias ativas Fotometria astronômica Nucleo galatico Espectros astronômicos |
topic |
Galáxias ativas Fotometria astronômica Nucleo galatico Espectros astronômicos Galaxies: active Galaxies: nuclei Galaxies: starburst Galaxies: stellar content |
dc.subject.eng.fl_str_mv |
Galaxies: active Galaxies: nuclei Galaxies: starburst Galaxies: stellar content |
description |
We present a spectroscopic study of the stellar populations of low-luminosity active galactic nuclei (LLAGNs). Our main goal is to determine whether the stars that live in the innermost (100 pc scale) regions of these galaxies are in some way related to the emission-line properties, which would imply a link between the stellar population and the ionization mechanism. High signal-to-noise ratio, ground-based long-slit spectra in the 3500– 5500 Å interval were collected for 60 galaxies: 51 LINERs and LINER/H II transition objects, two starburst galaxies, and seven nonactive galaxies. In this paper, the first of a series, we (1) describe the sample; (2) present the nuclear spectra; (3) characterize the stellar populations of LLAGNs by means of an empirical comparison with normal galaxies; (4) measure a set of spectral indices, including several absorption-line equivalent widths and colors indicative of stellar populations; and (5) correlate the stellar indices with emission-line ratios that may distinguish between possible excitation sources for the gas. Our main findings are as follows: (1) Few LLAGNs have a detectable young (~<10 7 yr) starburst component, indicating that very massive stars do not contribute significantly to the optical continuum. In particular, no features due to Wolf-Rayet stars were convincingly detected. (2) High-order Balmer absorption lines of HI (HOBLs), on the other hand, are detected in ~40% of LLAGNs. These features, which are strongest in 10 8–10 9 yr intermediate-age stellar populations, are accompanied by diluted metal absorption lines and bluer colors than other objects in the sample. (3) These intermediateage populations are very common (~50%) in LLAGNs with relatively weak [O I] emission ([O I/Hα ≤ 0.25) but rare (~10%) in LLAGNs with stronger [O I]. This is intriguing since LLAGNs with weak [O I] have been previously hypothesized to be ‘‘transition objects’’ in which both an AGN and young stars contribute to the emission-line excitation. Massive stars, if present, are completely outshone by intermediate-age and old stars in the optical. This happens in at least a couple of objects where independent UV spectroscopy detects young starbursts not seen in the optical. (4) Objects with predominantly old stars span the whole range of [O I]/Hα values, but (5) sources with significant young and/or intermediate-age populations are nearly all (~90%) weak– [O I] emitters. These new findings suggest a link between the stellar populations and the gas ionization mechanism. The strong–[O I] objects are most likely true LLAGNs, with stellar processes being insignificant. However, the weak–[O I] objects may comprise two populations, one where the ionization is dominated by stellar processes and another where it is governed by either an AGN or a more even mixture of stellar and AGN processes. Possible stellar sources for the ionization include weak starbursts, supernova remnants, and evolved poststarburst populations. These scenarios are examined and constrained by means of complementary observations and detailed modeling of the stellar populations in forthcoming communications. |
publishDate |
2004 |
dc.date.issued.fl_str_mv |
2004 |
dc.date.accessioned.fl_str_mv |
2015-01-14T02:15:56Z |
dc.type.driver.fl_str_mv |
Estrangeiro info:eu-repo/semantics/article |
dc.type.status.fl_str_mv |
info:eu-repo/semantics/publishedVersion |
format |
article |
status_str |
publishedVersion |
dc.identifier.uri.fl_str_mv |
http://hdl.handle.net/10183/108913 |
dc.identifier.issn.pt_BR.fl_str_mv |
0004-637X |
dc.identifier.nrb.pt_BR.fl_str_mv |
000503985 |
identifier_str_mv |
0004-637X 000503985 |
url |
http://hdl.handle.net/10183/108913 |
dc.language.iso.fl_str_mv |
eng |
language |
eng |
dc.relation.ispartof.pt_BR.fl_str_mv |
The astrophysical journal. Chicago. Vol. 605, no. 1, pt. 1 (Apr. 2004), p. 105-126 |
dc.rights.driver.fl_str_mv |
info:eu-repo/semantics/openAccess |
eu_rights_str_mv |
openAccess |
dc.format.none.fl_str_mv |
application/pdf |
dc.source.none.fl_str_mv |
reponame:Repositório Institucional da UFRGS instname:Universidade Federal do Rio Grande do Sul (UFRGS) instacron:UFRGS |
instname_str |
Universidade Federal do Rio Grande do Sul (UFRGS) |
instacron_str |
UFRGS |
institution |
UFRGS |
reponame_str |
Repositório Institucional da UFRGS |
collection |
Repositório Institucional da UFRGS |
bitstream.url.fl_str_mv |
http://www.lume.ufrgs.br/bitstream/10183/108913/1/000503985.pdf http://www.lume.ufrgs.br/bitstream/10183/108913/2/000503985.pdf.txt http://www.lume.ufrgs.br/bitstream/10183/108913/3/000503985.pdf.jpg |
bitstream.checksum.fl_str_mv |
968ffa7c5d04b986c925a5ac47db15d9 fd72d1d779e6b07255fade0910e81a53 1fb66dd6291e9053e8c36cd1dfba4e89 |
bitstream.checksumAlgorithm.fl_str_mv |
MD5 MD5 MD5 |
repository.name.fl_str_mv |
Repositório Institucional da UFRGS - Universidade Federal do Rio Grande do Sul (UFRGS) |
repository.mail.fl_str_mv |
|
_version_ |
1801224862278090752 |