Synthetic stellar populations: single stellar populations, stellar interior models and primordial protogalaxies

Abstract

We present a new set of stellar interior and synthesis models for predicting the integrated emission from stellar populations in star clusters and galaxies of arbitrary age and metallicity. This work differs from existing spectral synthesis codes in a number of important ways, namely (1) the incorporation of new stellar evolutionary tracks, with sufficient resolution in mass to sample rapid stages of stellar evolution; (2) a physically consistent treatment of evolution in the Hertzsprung–Russell (HR) diagram, including the approach to the main sequence and the effects of mass loss on the giant and horizontal branch phases. Unlike several existing models, ours yield consistent ages when used to date a coeval stellar population from a wide range of spectral features and colour indexes. We use Hipparcos data to support the validity of our new evolutionary tracks. We rigorously discuss degeneracies in the age–metallicity plane and show that inclusion of spectral features blueward of 4500 Å suffices to break any remaining degeneracy and that with moderate S/N spectra (10 per 20‐Å resolution element) age and metallicity are not degenerate. We also study sources of systematic errors in deriving the age of a single stellar population and conclude that they are not larger than 10–15 per cent. We illustrate the use of single stellar populations by predicting the colours of primordial protogalaxies and show that one can first find them and then deduce the form of the initial mass function (IMF) for the early generation of stars in the Universe. Finally, we provide accurate analytic fitting formulae for ultrafast computation of colours of single stellar populations.

Naked active galactic nuclei

“…To test this mechanism for the objects in our sample we have simulated the effect of reddening a Seyfert 1 type spectrum to the point where the broad Hβ line becomes washed out in the spectrum of the underlying galaxy to determine whether the blue continuum is still detectable. For a model quasar spectrum we used the composite from the FIRST bright quasar survey (Brotherton et al 2001), and for the underlying galaxy the models of Jimenez et al (2004). The top panel of Fig.…”

Evidence of short-lived SN Ia progenitors

“…Note that broadband colors are not sufficient to determine the star formation histories of galaxies, as they suffer from significant age-metallicity degeneracies (e.g. Jimenez et al 2004). In brief, VESPA uses singular value decomposition to calculate the number of significant components in the spectrum of a given galaxy.…”

Comprehensive cosmographic analysis by Markov chain method

“…The outcome of this process is a set of 12 values of the Hubble parameter versus redshift. A particularly nice feature of this test is that the sensitivity of differential ages to systematic error is lower than in the case of absolute ages ( [24]). …”