Issue |
Astron. Astrophys. Suppl. Ser.
Volume 118, Number 1, July 1996
|
|
---|---|---|
Page(s) | 89 - 103 | |
DOI | https://doi.org/10.1051/aas:1996183 | |
Published online | 15 July 1996 |
Ultraviolet properties of early-type galaxies*
1
Universidade Federal do Rio Grande do Sul, IF, CP 15051, Porto Alegre 91501–970, RS, Brazil
2
Observatoire de Paris/Meudon, URA 173 CNRS, F–92195 Meudon Principal Cedex, France
3
Canada-France-Hawaii Telescope, P.O. box 1597, Kamuela, Hawaii – 96743, U.S.A.
Send offprint request to: D. Alloin
Received:
9
October
1995
Accepted:
21
December
1995
We analyse the UV properties of early-type galaxies from
their UV spectra in the IUE library, including both normal and active
nuclei. We co-added the spectra, and hence the objects into groups of
similar spectral properties in the UV, also taking into account their
properties in the visible/near-infrared ranges. Although, owing to the
presence of a residual fixed pattern noise, IUE data cannot be
improved by co-addition as expected for spectra containing only
random noise, this procedure still provided
spectra of higher signal/noise ratio than in previous studies,
often based on individual spectra and therefrom derived colour
indices. Thanks to the co-adding procedure, information on
spectral features can now be assessed. The red stellar
population groups exhibit a far-UV flux
at different levels. The higher ones denote the presence of
the UV turnup, which possibly exhibits absorption features,
at least as detected through the IUE aperture. As to the blue stellar
population groups and/or
AGNs, we have carried
out simple syntheses with UV star cluster templates and galaxy spectra
in order to infer the properties such as burst ages and contamination by
an active nucleus. It has been possible to derive information on the
extinction law affecting some internally reddened galaxies; there are
cases where the presence of the Å absorption feature suggests a
reddening law similar to the Galactic one, and others without the
Å
feature, suggesting that it is rather an SMC type law which applies, then.
Key words: (ISM:) dust, extinction / galaxies: active / galaxies: elliptical and lenticular, cD / galaxies: general / galaxies: stellar content / ultraviolet: galaxies
© European Southern Observatory (ESO), 1996