Amit Kr. Ratewal

Amit Kr. Ratewal

Publications

Subaru HSC weak lensing of SDSS redMaPPer cluster satellite galaxies: Empirical upper limit on orphan fractions

Published in MNRAS, 2022

Gravitational lensing can directly estimate the matter distribution around objects. We measure the weak lensing signal around SDSS redMaPPer cluster satellite galaxies , induced on the shapes of galaxies background to them. We choose satellites where their central galaxy is defined with a probability $P_{\rm cen}>0.95$ in the redshift range, $0.1\leq z\leq 0.33$. For shape measurements, we use galaxies from the Subaru Hyper Suprime-Cam (HSC) survey. In order to understand the effect of the various environmental processes on matter distribution (mainly dark matter), we bin our satellite galaxies by their distance from the cluster center. Then we compare the matter distribution around satellites to a sample of galaxies that do not reside in clusters but have colors and magnitudes similar to the satellites. We see hints of a difference in the mass of the subhalo of the satellite compared to the halo masses of galaxies in our control sample, especially for the innermost cluster-centric radial bin $0.1< r < 0.3$ $[h^{-1}{\rm Mpc}]$. We use this observed mass difference to put a first ever direct upper limit on the prevalence of orphan galaxies that have lost most of their dark matter, primarily due to multiple pericentric passages. However, these upper limits could be relaxed if there is substantial contamination in the satellite galaxy sample.

Recommended citation: Kumar et al. 2022 MNRAS 517, 4389-4404 (2022)

Over-abundance of orphan galaxies in the UniverseMachine

Published in MNRAS Letters, 2024

Orphan galaxies are satellites that have lost most of their dark mass mainly due to multiple pericentric passages. We run a mock redMaPPer cluster finding algorithm on a simulated galaxy catalog which is constructed based on their star formation rate and merger histories. This mock cluster finding runs over each galaxy in the catalog without having prior information of central or satellite tag and tries to find the most massive galaxy based within its virial radius. We use satellite galaxies with characteristic stellar masses greater than 0.2 $L^*$, and evolving in heavy clusters ($M_{\rm BCG}$> 10$^{14}$ $h^{-1}M\odot$) to closely mimic actual redMaPPer satellites. We analyze the population of such orphans at various cluster centric distances and compare it to constraints from observations.

Recommended citation: Kumar et al. 2024 https://doi.org/10.1093/mnrasl/slae023

Stellar to halo mass relations for GAMA satellites

In Prep

For an infalling satellite galaxy, baryonic mass can dissipate energy and momentum via collisions; hence it can sink to the center more radially and efficiently. However, DM up to a very good approximation, can be considered dissipationless; hence due to tidal forces, the infalling satellite will lose most of its DM mass compared to its stellar mass. Cosmological hydrodynamical simulations (e.g. IllustrisTNG), show stellar-to-halo mass relation(SHMR) exhibit a larger scatter for satellites than central galaxies. For the same stellar mass, SHMR for satellites tends to exhibit lower dynamical masses than for centrals. Systematic deviation from central- SHMR is more prominent for satellites in a more massive host and at smaller cluster centric distances. Motivated from it, we use a sample of satellites from heavy galaxy groups ( $N_{\rm sat}>10$ \& $M_{\rm host}>10^{13} h^{-1}{\rm M_{\odot}}$) defined in Galaxy mass and assembly (GAMA) survey, and look for matter distribution around them, binned by their stellar masses. Using, 3 year shape catalog from Hyper suprime cam survey, which covers ~ 420 $deg^2$ sky area, we will be able to put tighter constrain on SMHM relations than previous studies.

Recommended citation: Kumar, More 2024 In Prep []