UV-extended E-MILES stellar population models: young components in massive early-type galaxies

Abstract

We present UV-extended E-MILES stellar population synthesis models covering\nthe spectral range 1680-50000A at moderately high resolution. We employ the\nNGSL space-based stellar library to compute spectra of single-age,\nsingle-metallicity stellar populations in the wavelength range from 1680 to\n3540A. These models represent a significant improvement in resolution and\nage/metallicity coverage over previous studies based on earlier space-based\nlibraries. These model spectra were joined with those we computed in the\nvisible using MILES, and other empirical libraries for redder wavelengths. The\nmodels span the metallicity range -1.79<[M/H]<+0.26 and ages above 30 Myr, for\na suite of IMF types with varying slopes. We focus on the behaviour of colours,\nspectra and line-strength indices in the UV range as a function of relevant\nstellar population parameters. Whereas some indices strengthen with increasing\nage and metallicity, as most metallicity indicators in the visible, other\nindices peak around 3 Gyr for metal-rich stellar populations, such as Mg at\n2800A. Our models provide reasonably good fits to the integrated colours and\nmost line-strengths of the stellar clusters of the Milky-Way and LMC. Our\nfull-spectrum fits in the UV range for a representative set of ETGs of varying\nmass yield age and metallicity estimates in very good agreement with those\nobtained in the optical range. The comparison of UV colours and line-strengths\nof massive ETGs with our models reveals the presence of young stellar\ncomponents, with ages in the range 0.1-0.5 Gyr and mass fractions 0.1-0.5%, on\nthe top of an old stellar population.\n