title: The true nature of LINER galaxies, weak AGN or strong stars
creator: Singh, Robert Artur
subject: ddc-520
subject: 520 Astronomy and allied sciences
description: Galaxies consist of dark matter, stars, dust and substantial amounts of mostly hydrogen gas and other  elements. A particular sub-class of galaxies are those which exhibit low-ionisation nuclear emission line  regions (LINERs) whose spectra predominantly show emission lines from weakly ionised atoms. When  first identified in 1980, it was clear that the necessary radiation field had to be different than stemming from  all previously known galaxies with an accreting super massive black hole, i.e. with an active galactic nucleus  (AGN). Various explanations were put forward, ranging from shock-ionisation, via young hot stars,  to the favoured ionisation by low-luminosity AGNs. The latter explanation has since become generally  accepted.  The analysis is based on a new dataset that combines, for the first time, a complete spectral and spatial  view on galaxies, whereas before either the spatial component was missing or spectral coverage for the  LINER diagnostic was insufficient. All regions across all individual galaxies are classified based on the  standard emission line ratio diagnostic (BPT) and show that regions with LINER-like emission at larger  galactocentric radial distances show a significant excess in flux than what would be expected from AGN  illumination. Furthermore evidence in support of the hypothesis of ionisation by hot old (post-AGB) stars  is obtained.  These results have two immediate consequences: it necessitates a substantial revision of previous work  on properties of AGN and their host galaxies where LINERs were assumed to be fully powered by the  accreting black hole, and secondly it also implies a possible simplification for unified models of black  hole accretion and feedback. In conclusion, our data rejects the low-luminosity AGN explanation as the  sole ionisation mechanism in LINER galaxies and supports the hypothesis of ionisation by hot old stars.
date: 2015
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/18226/1/thesis.pdf
identifier: DOI:10.11588/heidok.00018226
identifier: urn:nbn:de:bsz:16-heidok-182267
identifier:   Singh, Robert Artur  (2015) The true nature of LINER galaxies, weak AGN or strong stars.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/18226/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng