EDP Sciences
Free access
Volume 429, Number 3, January III 2005
Page(s) 819 - 823
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20041455

A&A 429, 819-823 (2005)
DOI: 10.1051/0004-6361:20041455

Peculiarities and populations in elliptical galaxies

II. Visual-near IR colours as population indices
R. Michard

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

(Received 11 June 2004 / Accepted 6 August 2004 )

As a complement to the data collected and discussed in Paper I of this series, 2MASS near-IR images have been used, in connection with available V light aperture photometry, to derive the colours V-J, V-K, J-H and J-K within the effective aperture $A_{\rm e}$: nearly the same complete sample of 110 E-type galaxies is treated. In Paper I these were classified, based on morphological criteria, into the "peculiar" (or Pec) and "normal" (or Nop) subsamples.

For the Nop subsample, the derived colour indices are tightly related to the galaxy masses, as measured by the central velocity dispersion $\sigma_0$, although with rather small slopes as regards J-H and J-K. For the Pec subsample, the V-J and V-K colours behave as UBV and line-indices: part of the objects show blue residuals from the appropriate colour- $\sigma_0$ regression, which is evidence of a younger population mixed with the "normal" one traced by the Nop regressions; the other shows no deviations from the Nop subsample. The distinction among Pec objects between the YP family (NGC 2865 type), and the NP one (NGC 3923 type), is statistically supported, and generally confirmed in specific cases.

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

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© ESO 2005