UV-radiation in galaxies |
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| Authors: | Olga K Sil’chenko |
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| Institution: | (1) Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA;(2) Astrophysics Division, SSD, European Space Agency, USA;(3) Departamento de Astrofisica, Facultad de Ciencias Fisicas, Universidad Complutense de Madrid, E-28040 Madrid, Spain; E-mail;(4) DAEC–URA173, Observatoire de Paris-Meudon, Place Jules Janssen, Meudon, F-92195, France |
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| Abstract: | I review the origin of UV-radiation in galaxies of different morphological types. UV-excess in spectra of massive elliptical
galaxies which have predominantly old stellar populations is traditionally explained by the contribution of low-mass stars
at very late, poorly known stages of evolution—by so called ‘AGB-manqué’ stars or by the population of extended horizontal
branch. However recent results from the GALEX survey of a large sample of nearby ellipticals have also demonstrated probable
traces of recent star formation in a third of all ellipticals observed. In spiral galaxies extended UV-disks have been discovered
by the GALEX; they are certainly illuminated by the current star formation, but what has provoked star formation in the areas
of very low gas density, beyond the distribution of older stars, is a puzzle yet. The UV-spectra of starburst galaxies or
starforming galactic nuclei are characterized by weak emission lines, if any, quite dissimilar to their optical spectra. |
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