Jonas Johansson, Daniel Thomas, Claudia Maraston
We discuss chemical enrichments of ~4000 SDSS early-type galaxies using as
tracers the element abundance ratios [C/Fe], [N/Fe], [O/Fe], [Mg/Fe], [Ca/Fe]
and for the first time for unresolved stellar populations [Ti/Fe]. We utilise
the stellar population models of absorption line indices from Thomas, Maraston
& Johansson (2011), which are based on the MILES stellar library. We confirm
previous results of increasing age, [Z/H] and [O/Fe] ratios (often represented
by [{\alpha}/Fe] in the literature) with velocity dispersion. We further derive
identical correlations with velocity dispersion for the abundance ratios
[O/Fe], [Mg/Fe] and [C/Fe], implying that C/Mg and C/O are close to solar
values. This sets a lower limit on the formation time-scales and star-burst
components of early-type galaxies to ~0.4 Gyr, which is the lifetime of a
3M\odot star, since the full C enrichment must be reached. [N/Fe] correlates
with velocity dispersion, but offset to lower values and with a steeper slope
compared to the other element ratios. We do not find any environmental
dependencies for the abundances of C and N, contrary to previous reports in the
literature. [Fe/H] does not correlate with velocity dispersion over the entire
parameter range covered, but for fixed age we find a steep trend for the
[Fe/H]-{\sigma} relation. This trend is weaker than the analogous for total
metallicity (which also shows steeper trends at fixed age) owing to the lower
Fe contribution from SN Ia for more massive early-type galaxies. We find
[Ca/Fe] ratios that are close to solar values over the entire velocity
dispersion range covered. Tentative, due to large scatter, the results for
[Ti/Fe] indicate that Ti follows the trends of Ca. This implies a significant
contribution from SN Ia to the enrichment of heavy {\alpha}-elements and puts
strong constraints on supernova nucleosynthesis and models of galactic chemical
evolution.
View original:
http://arxiv.org/abs/1112.0322
No comments:
Post a Comment