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BEGIN:VEVENT
DTSTART;TZID=Atlantic/Canary:20110210T000000
DTEND;TZID=Atlantic/Canary:20110210T010000
UID:iactalks-243
X-WR-CALNAME: IAC Talks: Open Astronomy Seminars
X-ORIGINAL-URL: /iactalks/Talks/view/243
CREATED:2011-02-10T00:00:00+00:00
X-WR-CALDESC: IAC Talks upcomming talks
SUMMARY:Ionization of the diffuse gas in galaxies: hot low-mass evolved sta
 rs at work
DESCRIPTION:Ionization of the diffuse gas in galaxies: hot low-mass evolved
  stars at work\nDr. Christophe Morisset\n\nWe revisit the question of the 
 ionization of the diffuse medium in late type galaxies, by studying NGC 89
 1, the prototype of edge-on spiral galaxies. The most important challenge 
 for the models considered so far was the observed increase of [O III]/H&be
 ta;, [O II]/Hβ and [N II]/Hα with increasing distance to the ga
 lactic plane. We propose a scenario based on the expected population of ma
 ssive OB stars and hot low-mass evolved stars (HOLMES) in this galaxy to e
 xplain this observational fact. In the framework of this scenario we const
 ruct a finely meshed grid of photoionization models. For each value of the
  galactic latitude z we look for the models which simultaneously fit the o
 bserved values of the [O III]/Hβ, [O II]/Hβ and [N II]/Hα 
 ratios. For each value of z we find a range of solutions which depends on 
 the value of the oxygen abundance. The models which fit the observations i
 ndicate a systematic decrease of the electron density with increasing z. T
 hey become dominated by the HOLMES with increasing z only when restricting
  to solar oxygen abundance models, which argues that the metallicity above
  the galactic plane should be close to solar. They also indicate that N/O 
 increases with increasing z.
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