Peculiarities and populations in elliptical galaxies

Free access article

Issue		A&A Volume 423, Number 3, September I 2004


Page(s)		833 - 847
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20035637

A&A 423, 833-847 (2004)
DOI: 10.1051/0004-6361:20035637

I. An old question revisited

R. Michard¹ and P. Prugniel²

¹ Observatoire de Paris, LERMA, 77 Av. Denfert-Rochereau, 75015 Paris, France
e-mail: raymond.michard@obspm.fr
² Centre de Recherches Astronomiques, Univ. Lyon 1, Observatoire de Lyon, 69561 St. Genis Laval Cedex, France

(Received 6 November 2003 / Accepted 26 March 2004)

Abstract
Morphological peculiarities, as defined from isophote asymmetries and number of detected shells, jets or similar features, have been estimated in a sample of 117 E classified galaxies, and qualified by an ad hoc $\Sigma_2$ index. The overall frequency of "peculiar" objects (Pec subsample) is 32.5%. It decreases with the cosmic density of the environment, being minimal for the Virgo cluster, the densest environment in the sampled volume. This environmental effect is stronger for galaxies with relatively large $\Sigma_2$ .

The Pec subsample objects are compared with "normal" objects (Nop subsample) as regards their basic properties. Firstly, they systematically deviate from the Fundamental Plane and the Faber-Jackson relation derived for the Nop subsample, being too bright for their mass. Secondly, the dust content of galaxies, as estimated from IRAS fluxes, are similar in both subsamples. Third, the same is true of the frequency of Kinematically Distinct cores (KDC), suggesting that KDC and morphological peculiarities do not result from the same events in the history of E-galaxies.

Using the Nop sample alone, we obtain very tight reference relations between stellar population indicators ( U-B, B-V, B-R, V-I, Mg ₂, H $\beta$ , $\langle{\rm Fe}\rangle$ , Mg b) and the central velocity dispersion $\sigma_0$ . The discussion of the residuals of these relations allows us to classify the Pec galaxies in two families i.e. the YP or NGC 2865 family, and the NP or NGC 3923 one. Galaxies in the first group show consistent evidence for a younger stellar population mixed with the old one, in agreement with classical results (Schweizer et al. 1990; Schweizer & Seitzer 1992). The second group, however, has "normal", or reddish, populations. It is remarkable that a fraction (circa 40%) of morphologically perturbed objects do not display any signature of a young population, either because the event responsible for the pecularity is too ancient, or because it did not produce significant star formation (or eventually that the young sub-population has high metallicity).

A preliminary attempt is made to interpret the populations of Pec objects by combining a young Single Stellar Population with a Nop galaxy, with only limited success, perhaps largely due to uncertainties in the SSP indices used.

Key words: galaxies: elliptical and lenticulars, CD -- galaxies: photometry

SIMBAD Objects
Tables at the CDS

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.