Absorption line indices in theUV

Abstract

Aims. Stellar absorption lines in the optical (e.g. the Lick system) have been extensively studied and constitute an important stellar population diagnostic for galaxies in the local universe and up to moderate redshifts. Proceeding towards higher look-back times, galaxies are younger and the ultraviolet becomes the relevant spectral region where the dominant stellar populations shine. A comprehensive study of ultraviolet absorption lines of stellar population models is however still lacking. With this in mind, we study absorption line indices in the far and mid-ultraviolet in order to determine age and metallicity indicators for UV-bright stellar populations in the local universe as well as at high redshift. Methods. We explore empirical and theoretical spectral libraries and use evolutionary population synthesis to compute synthetic line indices of stellar population models. From the empirical side, we exploit the IUE-low resolution library of stellar spectra and system of absorption lines, from which we derive analytical functions (fitting functions) describing the strength of stellar line indices as a function of gravity, temperature and metallicity. The fitting functions are entered into an evolutionary population synthesis code in order to compute the integrated line indices of stellar populations models. The same line indices are also directly evaluated on theoretical spectral energy distributions of stellar population models based on Kurucz high-resolution synthetic spectra, In order to select indices that can be used as age and/or metallicity indicators for distant galaxies and globular clusters, we compare the models to data of template globular clusters from the Magellanic Clouds with independently known ages and metallicities. Results. We provide synthetic line indices in the wavelength range ∼1200 Å to ∼3000 Å for stellar populations of various ages and metallicities.This adds several new indices to the already well-studied CIV and SiIV absorptions. Based on the comparison with globular cluster data, we select a set of 11 indices blueward of the 2000 Å rest-frame that allows us to recover well the ages and the metallicities of the clusters. These indices are ideal to study ages and metallicities of young galaxies at high redshift. We also provide the synthetic high-resolution stellar population SEDs.

On the spectral resolution of the MILES stellar library

“…Stellar libraries are a crucial ingredient in stellar population models that predict the spectral energy distributions of stellar populations (e.g., Worthey 1994;Fioc & Rocca-Volmerange 1997;Bruzual & Charlot 1993;Maraston 1998Maraston , 2005Maraston et al 2009a). The latter are a key tool for analysing unresolved stellar populations such as galaxies and extra-galactic star clusters.…”

GAMA: The effect of environment on galaxy emission line properties

“…We adopt the stellar population templates from Maraston & Strömbäck (2011) based on the MILES stellar library (Sánchez Blázquez et al 2006), extended in the blue for λ < 3500Å using theoretical spectra from the model of Maraston et al (2009) based on the theoretical library UVBLUE (Rodríguez-Merino et al 2005).…”

Open issues on the synthesis of evolved stellar populations at ultraviolet wavelengths

“…In Chavez et al (2009) we presented the first theoretical analysis of the UV integrated spectra of evolved SSPs (see also Maraston et al 2009, for young populations). We focused on particular absorption lines and blends to establish, through the use of spectroscopic indices, their behavior in terms of age and chemical Fig.…”