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

Environmental dependence on galaxy-halo connections for satellites using HSC weak lensing

Published in MNRAS, 2024

We present the luminosity-halo mass relations of satellite (sLHMRs) galaxies in the SDSS redMaPPer cluster catalogue and the effects of the dense cluster environment on subhalo mass evolution. We use data from the Subaru Hyper Suprime-Cam survey Year-3 catalogue of galaxy shapes to measure the weak lensing signal around these satellites. This signal serves as a probe of the matter distribution around the satellites, thereby providing the masses of their associated subhalos. We bin our satellites based on physical observable quantities such as their luminosity or the host cluster’s richness, combined with their cluster-centric radial separations. Our results indicate that although more luminous satellites tend to reside in more massive halos, the sLHMRs depend on the distance of the satellite from the cluster centre. Subhalos near the cluster centre (within <0.3 $[h^{-1}{Mpc}]$) are stripped of mass. Consequently, the ratio of subhalo mass to luminosity decreases near the cluster centre. For low luminosity galaxies (L<$10^{10} h^{-2}L_{sun}$), the lack of evidence of increasing subhalo masses with luminosity shows the impact of tidal stripping. We also present stellar-to-subhalo mass relations (sSHMRs) for our satellite sample evolving at different cluster-centric separations. Inferred sSHMRs in the outer radial bin appear to match that observed for the field galaxies. We show that the sSHMRs from the mock-redMaPPer run on galaxy catalogues generated by the empirical UniverseMachine galaxy formation model are in good agreement with our observational results. Satellites, when binned based on the host cluster’s richness, show very little dependence of the subhalo mass on the richness.

Recommended citation: Kumar et al. 2024

Halo assembly bias using splashback radius

In Prep

Gaussian fluctuations in initial homogeneous density fields results to structure formation as observed in the present day Universe. Observations suggest that the distribution of dark matter halos in the Universe is non-uniform, e.g. clustering in high mass halos is more common than low mass halos. Halo bias is a quantity which relates expectation value of halo over-density compared to the matter. Hence, galaxy clustering measurements when combined with halo bias, can give underlying dark matter distribution. Since weak gravitational lensing provides a good estimate of halo mass, one can use it to study bias-mass relationship. Clustering of halos also seem to depend on their assembly history along with their mass, a term known as halo assembly bias. Definition of the halo boundary has effect on implication of halo bias results from earlier studies, hence we propose to use a physically motivated definition for it i.e. Splashback radius, which is defined with the help of the first apocentric orbital radius of the particles. We use Erebos N-body simulations for this purpose.

Recommended citation: Garg, Kumar, More In prep. []

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 In prep []