AR-2019-2020

collaborators establish the conditional independence of bias and internal properties of halo at fixed α , and conclude that the tidal anisotropy of the environment of the halo plays a significant role in shaping the internal properties as well as its correlations to the large scale clustering. Observational Cosmology Signatures of self-interacting dark matter on cluster density profile and sub-halo distributions Currently astrophysical observations provide the best way to explore the particle physics properties of dark matter. Does dark matter have any interactions other than gravity? In this research work, by Surhud More and collaborators, large cosmological simulations were run including effects of different self-interactions of dark matter motivated from toy particle physics models. The focus of the study was to look at various observational properties of galaxy clusters such as the dependence on the number density profiles of satellite sub-halos and the density distribution of matter, in the presence of such interactions. It was shown that current weak lensing data can already put constraints on the self-interaction cross-section that are comparable to those obtained from the analysis of the Bullet Cluster. The splashback radius of optically selected clusters with Subaru HSC second public data release The edges of galaxy clusters, the so-called splashback radius, contain important information about how the galaxy clusters were assembled. The observed location of these edges in optically selected galaxy clusters, showed that they were about 20 percent smaller than expectations from the standard cosmological model. Surhud More and collaborators carried out research in which, the detection of the edges of galaxy clusters was extended to even earlier epochs in the Universe, as early as when it was just half its present age. This research made use of the data from the Subaru Hyper Suprime Cam survey. Tests on mock catalogues of galaxies showed that the new optical cluster finding algorithm used in the work was less susceptible to optical cluster selection effects. On the measurements of assembly bias and splashback radius using opti- cally selected galaxy clusters The galaxy clusters selected from large imaging surveys have been previously used to detect the edges of galaxy clusters and to study the effect of halo assembly bias. In this research work, Tomomi Sunayama, a postdoc from Japan, in collaboration with Surhud More , critically examined the methodology behind these observational detections with the help of mock galaxy catalogues. They mimicked the optical cluster detection algorithms and applied them to these mock catalogues to show that the optical cluster finding algorithm can induce selection effects which cause one to infer the presence of halo assembly bias, even when the signal is explicitly erased in the mock catalogue. The work also showed that the projection effects induced by the optical cluster finding can bias the inference of the edges of galaxy clusters, and thus, appropriate caution is warranted before interpreting these observations done using optically selected galaxy clusters. Kinematics of cluster galaxies and their relation to galaxy evolution Surhud More and collaborators studied the kinematics of galaxies within massive clusters to probe the physics of quenching of star forming galaxies within galaxy clusters. It was shown using numerical simulations of dark matter, that the kinematics of satellite galaxies can provide information about galaxy infall that is complementary to the (instantaneous) spatial distribution of satellites. This kinematic information can help distinguish between models of galaxy quenching