Peculiarities and populations in elliptical galaxies

Abstract

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 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.