Peculiar early-type galaxies in the SDSS Stripe82
  We explore the properties of `peculiar' early-type galaxies (ETGs) in the
local Universe, that show (faint) morphological signatures of recent
interactions such as tidal tails, shells and dust lanes. Standard-depth (51s
exposure) multi-colour galaxy images from the Sloan Digital Sky Survey (SDSS)
are combined with the significantly (2 mags) deeper monochromatic images from
the public SDSS Stripe82 to extract, through careful visual inspection, a
robust sample of nearby, luminous ETGs, including a subset of ~70 peculiar
systems. 18% of ETGs exhibit signs of disturbed morphologies (e.g. shells),
while 7% show evidence of dust lanes and patches. The peculiar ETG population
is found to preferentially inhabit low-density environments (outskirts of
clusters, groups or the field). An analysis of optical emission-line ratios
indicates that the fraction of peculiar ETGs that are Seyferts or LINERs
(19.4%) is twice the corresponding values in their relaxed counterparts
(10.1%). LINER-like emission is the dominant type of nebular activity in all
ETG classes, plausibly driven by stellar photoionisation associated with recent
star formation. An analysis of UV-optical colours indicates that, regardless of
the luminosity range being considered, the fraction of peculiar ETGs that have
experienced star formation in the last Gyr is a factor of ~1.5 higher than that
in their relaxed counterparts. The spectro-photometric results strongly suggest
that the interactions that produce the morphological peculiarities also induce
low-level recent star formation which, based on the recent literature, are
likely to contribute a few percent of the stellar mass over the last 1 Gyr. The
catalogue of galaxies that forms the basis of this paper can be obtained at:
http://www.mssl.ucl.ac.uk/~ska/stripe82/skaviraj_stripe82.dat or on request
from the author.
