The density of dark matter haloes of early-type galaxies in low-density
  environments
  New photometric and long-slit spectroscopic observations are presented for
NGC 7113, PGC 1852, and PGC 67207 which are three bright galaxies residing in
low-density environments. The surface-brightness distribution is analysed from
the K_S-band images taken with adaptive optics at the Gemini North Telescope
and the ugriz-band images from the Sloan Digital Sky Survey while the
line-of-sight stellar velocity distribution and line-strength Lick indices
inside the effective radius are measured along several position angles. The
age, metallicity, and alpha-element abundance of the galaxies are estimated
from single stellar-population models. In spite of the available morphological
classification, images show that PGC 1852 is a barred spiral which we do not
further consider for mass modelling. The structural parameters of the two
early-type galaxies NGC 7113 and PGC 67207 are obtained from a two-dimensional
photometric decomposition and the mass-to-light ratio of all the (luminous and
dark) mass that follows the light is derived from orbit-based axisymmetric
dynamical modelling together with the mass density of the dark matter halo. The
dynamically derived mass that follows the light is about a factor of 2 larger
than the stellar mass derived using stellar-population models with Kroupa
initial mass function. Both galaxies have a lower content of halo dark matter
with respect to early-type galaxies in high-density environments and in
agreement with the predictions of semi-analytical models of galaxy formation.
