Constraints provided by star cluster spectra on the nature of the UV turn-up in giant elliptical galaxies

Details Constraints provided by star cluster spectra on the nature of the UV turn-up in giant elliptical galaxies Constraints provided by star cluster spectra on the nature of the UV turn-up in giant elliptical galaxies

Mar 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988a%26a...192...98b&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 192, no. 1-2, March 1988, p. 98-106.

Astronomy and Astrophysics

Astronomy

21

Astronomical Spectroscopy, Elliptical Galaxies, Galactic Nuclei, Galactic Radiation, Star Clusters, Ultraviolet Radiation, Horizontal Branch Stars, Infrared Astronomy, Star Formation Rate, Ultraviolet Astronomy

Scientific paper

We have linked available ultraviolet observations to the visible and near infrared spectra of some objects from our star cluster and galaxy nucleus samples. We have analyzed the nature of the UV turn-up in giant elliptical galaxies (gE) in the light of our recent population synthesis results which are based upon a library of star cluster integrated spectra in the visible and near infrared. We also investigate how star clusters can provide information on the frequency of occurrence of particular types of stars with respect to the associated populations of a given age and metallicity. We definitely exclude the possibility that the UV turn-up in gE is caused by blue horizontal branch (BHB) stars associated with metal-poor components: even if they were a major contributor to the optical spectrum, their UV turn-up would be unable to account for that observed in gE, simply because it is not steep enough. Furthermore, our previous visible-near infrared synthesis has shown that only 10% of the flux originates from low metallicity components. On the contrary we find strong evidence that this UV turn-up is a result of on-going star formation in gE nuclei. Indeed, young blue clusters and/or H II region spectra match the UV turn-up quite well, without affecting much the optical range where their contribution is less than 2% at 5870 Å. Another possibility would be that the UV turn-up in gE is caused by post AGB stars from metal-rich components: data presently available about their frequency of occurrence in metal-rich galactic clusters, as well as about that of planetary nebulae in the bulge of M31 do not favour this interpretation however.

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