Compact Groups analysis using weak gravitational lensing
  We present a weak lensing analysis of a sample of SDSS Compact Groups (CGs).
Using the measured radial density contrast profile, we derive the average
masses under the assumption of spherical symmetry, obtaining a velocity
dispersion for the Singular Isothermal Spherical model, $\sigma_V = 270 \pm 40
\rm ~km~s^{-1}$, and for the NFW model, $R_{200}=0.53\pm0.10\,h_{70}^{-1}\,\rm
Mpc$. We test three different definitions of CGs centres to identify which best
traces the true dark matter halo centre, concluding that a luminosity weighted
centre is the most suitable choice. We also study the lensing signal dependence
on CGs physical radius, group surface brightness, and morphological mixing. We
find that groups with more concentrated galaxy members show steeper mass
profiles and larger velocity dispersions. We argue that both, a possible lower
fraction of interloper and a true steeper profile, could be playing a role in
this effect. Straightforward velocity dispersion estimates from member
spectroscopy yields $\sigma_V \approx 230 \rm ~km~s^{-1}$ in agreement with our
lensing results.
