| Abstract: |
Groups and clusters of galaxies gradually form over cosmic time via the gravitational collapse of the peaks of primordial density perturbations.
The identification and quantification of the total virialized mass of these structures is an important endeavour in cosmology for several reasons.
Firstly, their number density per unit mass, encoded in the halo mass function, is sensitive to cosmological parameters.
Secondly, the dense environment of groups and clusters plays a key role in galaxy evolution via mechanisms such as ram-pressure stripping,
harassment & tidal stripping. Primarily for these two motivations, it is important to determine the relationship between halo mass and various other observables (such as richness or X-ray luminosity (Lx)),
over a wide range in mass scales. In this talk, I will focus on a large sample of groups and low mass clusters detected through their extended X-ray emission in the COSMOS survey.
I will show that the X-ray detections span a more complete and wide range of redshift and mass space than detections via lensing maps. Although,
these structures may be challenging to detect directly through shear, once they have been identified,
their dark-matter content can be studied by using weak lensing stacking techniques.
Using this method, I will show how halo profiles and masses can be determined for the COSMOS X-ray sample.
In particular, I will present the first calibration of the Lx - mass relation at scales of Mass ~ 1013.5 solar masses by combining X-ray and the weak lensing
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