Peculiarities and populations in elliptical galaxies

Free access article

Issue		A&A Volume 449, Number 2, April II 2006


Page(s)		519 - 532
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20053923

A&A 449, 519-532 (2006)
DOI: 10.1051/0004-6361:20053923

III. Dating the last star formation event

R. Michard

Observatoire de Paris, LERMA, 77 Av. Denfert-Rochereau, 75015 Paris, France
e-mail: raymond.michard@obspm.fr

(Received 26 July 2005 / Accepted 17 November 2005 )

Abstract
Using 6 colours and 4 Lick line-indices we derive two-component models of the populations of ellipticals, involving a "primary" and a "juvenile" population. The first component is defined by the regressions of indices against the central velocity dispersion found in Papers I and II for the ${\it Nop}$ sample of non-peculiar objects. The second one is approximated by an SSP, and the modeling derives its age A, metallicity Z and fractional V-luminosity q_V, the fractional mass q_M being found therefrom. The model is designed for "blueish" peculiar galaxies, i.e. the ${\it Pec}$ sample and NGC 2865 family in the terminology of Paper I. The morphological peculiarities and the population anomaly are then believed to involve the same event, i.e. a merger plus starburst. It is possible to improve the models in a few cases by introducing diffuse dust (as suggested by far IR data), and/or by taking into account the fact that Lick- and colour indices do not relate to identical galaxy volumes. In most of the cases, the mass ratio of young stars q_M seems too small for the product of a recent major merger: the events under consideration might be minor mergers bringing "the final touch" to the build-up of the structure of the E-type object. The same modeling has been successfully applied to blueish galaxies of the ${\it Nop}$ sample, without morphological peculiarities however, to support the occurence of a distinct perturbing event. A few reddish objects of the ${\it Pec}$ sample (NGC 3923 family) and of the ${\it Nop}$ sample are also modeled, in terms of an excess of high metallicity stars, or diffuse dust, or both, but the results are inconclusive.

Key words: galaxies: elliptical and lenticulars, CD

SIMBAD Objects

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.