Bibcode
Singh, R.; van de Ven, G.; Jahnke, K.; Lyubenova, M.; Falcón-Barroso, J.; Alves, J.; Cid Fernandes, R.; Galbany, L.; García-Benito, R.; Husemann, B.; Kennicutt, R. C.; Marino, R. A.; Márquez, I.; Masegosa, J.; Mast, D.; Pasquali, A.; Sánchez, S. F.; Walcher, J.; Wild, V.; Wisotzki, L.; Ziegler, B.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 558, id.A43, 8 pp.
Advertised on:
10
2013
Revista
Número de citas
257
Número de citas referidas
242
Descripción
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.
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