Luminous Satellites of Early-Type Galaxies I: Spatial Distribution
  We study the spatial distribution of faint satellites of intermediate
redshift (0.1<z<0.8), early-type galaxies, selected from the GOODS fields. We
combine high resolution HST images and state-of-the-art host subtraction
techniques to detect satellites of unprecedented faintness and proximity to
intermediate redshift host galaxies (up to 5.5 magnitudes fainter and as close
as 0."5/2.5 kpc to the host centers). We model the spatial distribution of
objects near the hosts as a combination of an isotropic, homogenous
background/foreground population and a satellite population with a power law
radial profile and an elliptical angular distribution. We detect a significant
population of satellites, Ns =1.7 (+0.9,-0.8) that is comparable to the number
of Milky Way satellites with similar host-satellite contrast.The average
projected radial profile of the satellite distribution is isothermal, gamma_p=
-1.0(+0.3,-0.4), which is consistent with the observed central mass density
profile of massive early-type galaxies. Furthermore, the satellite distribution
is highly anisotropic (isotropy is ruled out at a >99.99% confidence level).
Defining phi to be the offset between the major axis of the satellite spatial
distribution and the major axis of the host light profile, we find a maximum
posterior probability of phi = 0 and |phi| less than 42 degrees at the 68%
confidence level. The alignment of the satellite distribution with the light of
the host is consistent with simulations, assuming that light traces mass for
the host galaxy as observed for lens galaxies. The anisotropy of the satellite
population enhances its ability to produce the flux ratio anomalies observed in
gravitationally lensed quasars.
