Ultraviolet properties of early-type galaxies

Abstract

Abstract. -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 λ2200Å absorption feature suggests a reddening law similar to the Galactic one, and others without the λ2200Å feature, suggesting that it is rather an SMC type law which applies, then.

Physical parameters of rich LMC clusters from modeling of deep HST colour–magnitude diagrams

“…Our value ([Fe/H] = −0.2) is closer to the upper boundary of these estimates, where most of the more recent determinations are also found (Olszewski et al 1991;Vallenari et al 1992;Bonatto et al 1995). Ages also span a significant range in the literature.…”

“…Ages also span a significant range in the literature. More recent determinations are within 8.4 ≤ log(τ/yr) ≤ 8.7 (Meurer et al 1990;Olszewski et al 1991;Vallenari et al 1992;Bonatto et al 1995;Fig. 24.…”

“…For metallicity, the most reliable determinations are within −0.9 < ∼ [Fe/H] < ∼ −0.4 (Meliani et al 1994 (spectra of 5 red supergiants); Bonatto et al 1995 (UV spectra); Oliva & Origlia 1998 (IR spectra)). Our result ([Fe/H] ≈ −0.6) is consistent with this range.…”

Nuclear Activity in Nearby Galaxies

“…A number of approaches have been adopted to construct the template. These include using (1) the spectrum of an off-nuclear position within the same galaxy (e.g., Storchi-Bergmann, Baldwin & Wilson 1993); (2) the spectrum of a different galaxy devoid of emission lines (e.g., Costero & Osterbrock 1977;Filippenko & Halpern 1984;; (3) a weighted linear combination of the spectra of a number different galaxies, chosen to best match the stellar population and velocity dispersion (Ho, Filippenko & Sargent 1997a); (4) a variant of (3), but employing a stellar library and simultaneously fitting for the emission lines and accounting for dust reddening ); (5) a mean spectrum derived from a principal-component analysis of a large set of galaxies (Hao et al 2005a); and (6) a model spectrum constructed from population synthesis techniques, using as input a library of spectra of either individual stars (e.g., Keel 1983c), synthesis models (e.g., Tremonti et al 2004;Sarzi et al 2005), or star clusters (e.g., Bonatto, Bica & Alloin 1989). Some studies (e.g., Kim et al 1995) implicitly assume that only the hydrogen Balmer lines are contaminated by starlight and that the absorption-line component can be removed by assuming a constant equivalent width (EW = 2 − 3Å).…”

Near IR spectroscopy of active galactic nuclei

“…From a stellar population study based on ultraviolet spectra, Bonatto et al (2000) claim that an old bulge stellar population is the dominant contributor, with indications of a series of previous bursts of star formation.…”