The spatial distribution and origin of the FUV excess in early-type
  galaxies
  We present surface photometry of a sample of 52 galaxies from the GALEX and
2MASS data archives, these include 32 normal elliptical galaxies, 10
ellipticals with weak Liner or other nuclear activity, and 10 star forming
ellipticals or early-type spirals. We examine the spatial distribution of the
Far Ultra-Violet excess in these galaxies, and its correlation with dynamical
and stellar population properties of the galaxies. From aperture photometry we
find that all galaxies except for recent major remnants and galaxies with
ongoing star formation show a positive gradient in the (FUV-NUV) colour
determined from the GALEX images. The logarithmic gradient does not correlate
with any stellar population parameter, but it does correlate with the central
velocity dispersion. The strength of the excess on the other hand, correlates
with both [alpha/Fe] and [Z/H], but more strongly with the former. We derive
models of the underlying stellar population from the 2MASS H-band images, and
the residual of the image from this model reveals a map of the centrally
concentrated FUV excess. We examine a possible hypothesis for generating the
FUV excess and the radial gradient in its strength, involving a helium
abundance gradient set up early in the formation process of the galaxies. If
this hypothesis is correct, the persistence of the gradients to the present day
places a strong limit on the importance of dry mergers in the formation of
ellipticals.
