Issue |
A&A
Volume 558, October 2013
|
|
---|---|---|
Article Number | A43 | |
Number of page(s) | 8 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/201322062 | |
Published online | 01 October 2013 |
The nature of LINER galaxies:
Ubiquitous hot old stars and rare accreting black holes
1
Max-Planck-Institut für Astronomie (MPIA),
Königstuhl 17,
69117
Heidelberg,
Germany
2
Instituto de Astrofísica de Canarias (IAC),
38205, La Laguna, Tenerife, Spain
3
Depto. Astrofísica, Universidad de La Laguna (ULL),
38206, La Laguna, Tenerife, Spain
4
University of Vienna, Türkenschanzstrasse 17, 1180
Vienna,
Austria
5
Departamento de Física, Universidade Federal de Santa
Catarina, PO Box 476,
88040-900
Florianópolis, SC, Brazil
6
CENTRA - Centro Multidisciplinar de Astrofísica, Instituto
Superior Técnico, Av. Rovisco Pais
1, 1049-001
Lisbon,
Portugal
7
Instituto de Astrofísica de Andalucía (CSIC),
Glorieta de la Astronomía s/n,
18008
Granada,
Spain
8
Leibniz-Institut für Astrophysik Potsdam (AIP),
An der Sternwarte 16,
14482
Potsdam,
Germany
9
Centro Astronómico Hispano Alemán, Calar Alto, (CSIC-MPG), C/Jesús
Durbán Remón 2-2, 04004
Almería,
Spain
10
Astronomisches Rechen Institut, Zentrum für Astronomie der
Universität Heidelberg, Mönchhofstrasse 12-14, 69120
Heidelberg,
Germany
11
SUPA, School of Physics and Astronomy, University of St
Andrews, North
Haugh, St Andrews,
KY16 9SS,
UK
12
Institute of Astronomy, University of Cambridge,
Madingley Road, Cambridge
CB3 0HA,
UK
13
CEI Campus Moncloa, UCM-UPM, Departamento de Astrofísica y CC. de
la Atmósfera, Facultad de CC. Físicas, Universidad Complutense de
Madrid, Avda. Complutense
s/n, 28040
Madrid,
Spain
Received: 12 June 2013
Accepted: 8 August 2013
Context. Galaxies, which often contain ionised gas, sometimes also exhibit a so-called low-ionisation nuclear emission line region (LINER). For 30 years, this was attributed to a central mass-accreting supermassive black hole (more commonly known as active galactic nucleus, AGN) of low luminosity, making LINER galaxies the largest AGN sub-population, which dominate in numbers over higher luminosity Seyfert galaxies and quasars. This, however, poses a serious problem. While the inferred energy balance is plausible, many LINERs clearly do not contain any other independent signatures of an AGN.
Aims. Using integral field spectroscopic data from the CALIFA survey, we compare the observed radial surface brightness profiles with what is expected from illumination by an AGN.
Methods. Essential for this analysis is a proper extraction of emission lines, especially weak lines, such as Balmer Hβ lines, which are superposed on an absorption trough. To accomplish this, we use the GANDALF code, which simultaneously fits the underlying stellar continuum and emission lines.
Results. For 48 galaxies with LINER-like emission, we show that the radial emission-line surface brightness profiles are inconsistent with ionisation by a central point-source and hence cannot be due to an AGN alone.
Conclusions. The most probable explanation for the excess LINER-like emission is ionisation by evolved stars during the short but very hot and energetic phase known as post-AGB. This leads us to an entirely new interpretation. Post-AGB stars are ubiquitous and their ionising effect should be potentially observable in every galaxy with the gas present and with stars older than ~1 Gyr unless a stronger radiation field from young hot stars or an AGN outshines them. This means that galaxies with LINER-like emission are not a class defined by a property but rather by the absence of a property. It also explains why LINER emission is observed mostly in massive galaxies with old stars and little star formation.
Key words: galaxies: active / galaxies: ISM / galaxies: nuclei / stars: AGB and post-AGB
© ESO, 2013
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