# Compact Groups analysis using weak gravitational lensing

## TL;DR

This paper uses weak gravitational lensing to analyze the mass distribution of SDSS Compact Groups, comparing models and examining how group properties affect the lensing signal, providing new insights into their dark matter halos.

## Contribution

It introduces a detailed weak lensing analysis of SDSS Compact Groups, evaluating different center definitions and the impact of group properties on mass profiles and velocity dispersions.

## Key findings

- Luminosity weighted center best traces dark matter halo center.
- Groups with concentrated galaxies have steeper mass profiles.
- Lensing-derived velocity dispersion agrees with spectroscopic estimates.

## Abstract

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.