The nature of LINER galaxies:. Ubiquitous hot old stars and rare accreting black holes

Author(s)

, R Singh, G. van de Ven, K. Jahnke, M. Lyubenova, J. Falcón-Barroso, J. Alves, R. Cid Fernandes, L. Galbany, R. García-Benito, B. Husemann, R. C. Kennicutt, R. A. Marino, I. Márquez, J. Masegosa, D. Mast, A. Pasquali, S. F. Sánchez, J. Walcher, V. Wild, L. Wisotzki, B. Ziegler

Abstract

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.

Organisation(s)

Department of Astrophysics

External organisation(s)

Max-Planck-Institut für Astronomie, University of La Laguna, Institute of Astrophysics of the Canary Islands, Universidade Federal de Santa Catarina, Instituto Superior Técnico, Spanish National Research Council (CSIC), Leibniz-Institut für Astrophysik Potsdam, University of Cambridge, Universidad Complutense de Madrid, Scientific Software Center, University of St. Andrews

Journal

Astronomy & Astrophysics

Volume

558

No. of pages

ISSN

0004-6361

DOI

https://doi.org/10.1051/0004-6361/201322062

Publication date

10-2013

Peer reviewed

Yes

Austrian Fields of Science 2012

103004 Astrophysics, 103003 Astronomy

Keywords

Portal url

https://ucrisportal.univie.ac.at/en/publications/2e272a69-457b-40cf-9077-410cad59ab33