arXiv subjects

Himansh Rathore

Publications and source records attributed to Himansh Rathore.

8 recordsLinked to original sources

arXiv2026

The Role of Dark Matter in Driving Disk Perturbations: Application to LMC-SMC Like Galaxy Interactions

Dark-matter (DM) models predict that satellite galaxies distort their host's DM halo. As such, both the satellite and the distorted halo can perturb the host's stellar disk. The LMC-SMC system is a nearby $\sim1:10$~mass-ratio binary with a well-constrained orbit and well-characterized LMC disk perturbations. Hence, the system offers unique opportunities to test DM theory, provided the impact of halo torques on the LMC's disk can be characterized along with the SMC's torques. We use halo Basis Function Expansions (BFEs) of an N-body simulation of an isolated LMC-SMC-like interaction to quantify the time-dependent torques exerted on the LMC's disk by the SMC and the LMC's DM halo. We find that the halo torques arise from the quadrupole halo distortion, and the inner (R$<6$ kpc) LMC disk warps are the most promising probe of this quadrupole. For the first time, we construct a BFE to quantify the LMC's disk perturbations resulting from the SMC and halo torques. We find that the LMC's disk is significantly perturbed prior to the Clouds' Milky Way infall, possessing warps with a mean vertical extent of $\sim1$ kpc. Finally, we apply multi-channel singular spectral analysis (mSSA) to the time-series of the disk BFE coefficients, halo quadrupole, and the LMC-SMC orbit. mSSA successfully separates the temporal evolution of the LMC warps into components correlated with the halo versus the SMC. Our framework identifies correlated evolution between the LMC's halo distortions and the LMC's disk perturbations, enabling the Clouds to be a precision laboratory for DM physics.

astro-ph.GA↗

arXiv2026

Mapping the Distorted Dark Matter Distribution of the LMC-SMC System Prior to Milky Way Infall with Basis Function Expansions

The SMC orbits within the LMC's dark matter (DM) halo in a $\sim$1:10 mass-ratio encounter. The LMC:Milky Way (MW) interaction is also $\sim$1:10, and is expected to perturb the MW's DM distribution. However, no framework exists to quantify the severity of these perturbations over multiple pericenters and longer periods of time, such as the LMC-SMC interaction history. We construct basis function expansions of a high-resolution \textit{N}-body simulation of the Clouds interacting in isolation and analyze their DM distributions at an epoch approximating the time of their infall to the MW. Our goal is to quantify how the Clouds distort each other's DM distributions \textit{without} the MW. The LMC halo's response to the SMC includes a $\sim 20$ kpc long dynamical friction wake and the displacement of the LMC's density center during each SMC pericenter, which produces two overdensities in the LMC halo (at $\sim$60 and $\sim$100 kpc) at MW infall. The SMC's tidal radius at infall is just $\sim4$ kpc, at which point the SMC has lost two-thirds of its initial DM mass to the LMC. The distortions to the Clouds' halos produce a highly asymmetric acceleration field. Accurate orbit integration in the LMC-SMC system must account for the time-dependent shapes of both halos. The SMC-induced perturbations in the LMC DM halo resemble the MW-LMC system, and persist over multiple SMC pericenters. We conclude that 1:10 satellite-host encounters induce characteristic deformations in both DM halos across host-mass scales, with implications for merger rates and tests of DM models.

astro-ph.GA↗

arXiv2026

A Statistical Framework to Identify Kinematically Outlying LMC Globular Clusters and Implications for the LMC's Dark Matter Profile

The LMC's Globular Clusters (GCs) bring a novel opportunity to understand the LMC's assembly history and dark matter (DM) properties, provided the kinematically outlying GCs can be reliably identified. However, traditional diagnostics like the Energy-Angular Momentum space fail because of large uncertainties on the GC velocities. In this work, we develop a new, robust statistical framework for identifying kinematically outlying LMC GCs, by using their Gaia-DR3 Proper Motions (PMs) combined with previous Line-of-Sight (LoS) velocity measurements. We use the difference between a GC's velocity vector and the average velocity vector of the surrounding red clump stars as a metric for quantifying a GC's kinematic peculiarity. We account for both the velocity measurement uncertainties and the LMC's intrinsic velocity dispersion. We find 5 LMC GCs to be kinematically outlying based on PM differences alone, and additional 6 GCs if LoS velocity information is also used. Majority of the GCs with outlying PMs are clustered at a distance of 3-4 kpc from the LMC center. The inclusion of outlying LMC GCs introduces a bias of upto 30% in the LMC's enclosed mass estimates derived using GCs as dynamical tracers; caution must be exercised in choosing the GC sample for precisely determining the LMC's DM content. We discuss the possibility that the kinematically outlying LMC GCs may be located in the LMC's elusive stellar halo and/or they could be accreted from external galaxies. Our work thus motivates future spectroscopic follow-up of these outlying GCs.

astro-ph.GA↗

arXiv2025

A Galactic Transformation -- Understanding the SMC's Structural and Kinematic Disequilibrium

The SMC is in disequilibrium. Gas line-of-sight (LoS) velocity maps show a gradient of $60-100$ km s$^{-1}$, generally interpreted as a rotating gas disk consistent with the Tully-Fisher relation. Yet, the stars don't show rotation. Despite a small on-sky extent ($\sim4$ kpc), the SMC exhibits a large ($\sim10$ kpc) LoS depth, and the stellar photometric center is offset from the HI kinematic center by $\sim$1 kpc. With N-body hydrodynamical simulations, we show that a recent ($\sim$100 Myr ago) SMC-LMC collision (impact parameter $\sim2$ kpc) explains the observed SMC's internal structure and kinematics. The simulated SMC is initialized with rotating stellar and gaseous disks. Post-collision, the SMC's tidal tail accounts for the large LoS depth. The SMC's stellar kinematics become dispersion dominated ($v/\sigma\approx0.2$), with radially outward motions at $R>2$ kpc, and a small ($<10$ km s$^{-1}$) remnant rotation at $R<2$ kpc, consistent with observations. Post-collision gas kinematics are also dominated by radially outward motions, without remnant rotation. Hence, the observed SMC's gas LoS velocity gradient is due to radial motions as opposed to disk rotation. Ram pressure from the LMC's gas disk during the collision imparts $\approx30$ km s$^{-1}$ kick to the SMC's gas, sufficient to destroy gas rotation and offset the SMC's stellar and gas centers. Our work highlights the critical role of group processing through galaxy collisions in driving dIrr to dE/dSph transformation, including the removal of gas. Consequently, frameworks that treat the SMC as a galaxy in transformation are required to effectively use its observational data to constrain interstellar medium and dark matter physics.

astro-ph.GA↗

arXiv2025

Response of the LMC's Bar to a Recent SMC Collision and Implications for the SMC's Dark Matter Profile

The LMC's stellar bar is offset from the outer disk center, tilted from the disk plane, and does not drive gas inflows. These properties are atypical of bars in gas-rich galaxies, yet the LMC bar's strength and radius are similar to typical barred galaxies. Using N-body hydrodynamic simulations, we show that the LMC's unusual bar is explainable if there was a recent collision (impact parameter $\approx$2 kpc) between the LMC and SMC. Pre-collision, the simulated bar is centered and co-planar. Post-collision, the simulated bar is offset ($\approx$1.5 kpc) and tilted ($\approx8.6^\circ$). The simulated bar offset reduces with time, and comparing with the observed offset ($\approx0.8$ kpc) suggests the timing of the true collision to be 150-200 Myr ago. 150 Myr post-collision, the LMC's bar is centered with its dark matter halo, whereas the outer disk center is separated from the dark matter center by $\approx1$ kpc. The SMC collision produces a tilted-ring structure for the simulated LMC, consistent with observations. Post-collision, the simulated LMC bar's pattern speed decreases by a factor of two. We also provide a generalizable framework to quantitatively compare the LMC's central gas distribution in different LMC-SMC interaction scenarios. We demonstrate that the SMC's torques on the LMC's bar during the collision are sufficient to explain the observed bar tilt, provided the SMC's total mass within 2 kpc was $(0.8-2.4) \times 10^9$ M$_\odot$. Therefore, the LMC bar's tilt constrains the SMC's pre-collision dark matter profile, and requires the SMC to be a dark matter-dominated galaxy.

astro-ph.GA↗

arXiv2024

Precise Measurements of the LMC Bar's Geometry With Gaia DR3 and a Novel Solution to Crowding Induced Incompleteness in Star Counting

We present new measurements of the two-dimensional (2-D) geometry of the LMC's stellar bar with precise astrometric observations of red clump stars in Gaia DR3. We develop a novel solution to tackle crowding induced incompleteness in Gaia datasets with the Gaia BP-RP color excess. Utilizing the color excess information, we derive a 2-D completeness map of the LMC's disk. We find that incompleteness biases the bar measurements and induces large uncertainties. With the completeness-corrected 2-D red clump map, we precisely measure the LMC bar's properties for the first time using Fourier decomposition. The bar radius is $R_{bar} = 2.13^{+0.03}_{-0.04}$ kpc, and its position angle is $121.26^{\circ} \pm 0.21^{\circ}$. The bar's strength as quantified by the Fourier bi-symmetric amplitude is $S_{bar} = 0.27$, indicating that the LMC has a significant bar perturbation. We find the bar has an axis ratio of $0.54 \pm 0.03$, and is offset with respect to the center of the outer disk isophote at R $\approx$ 5 kpc by $0.76 \pm 0.01$ kpc. These LMC bar properties agree with a hydrodynamic model where the SMC has undergone a recent direct collision with the LMC. We compare the LMC's bar properties with other barred galaxies in the local universe, and discover that the LMC is similar to other barred galaxies in terms of bar-galaxy scaling relations. We discuss how our completeness correction framework can be applied to other systems in the Local Group.

astro-ph.GA↗

arXiv2024

A gravitational constant transition within cepheids as supernovae calibrators can solve the Hubble tension

Local universe measurements of the Hubble constant (H0) using SNe Ia with Cepheids as calibrators yield a value of H0 which is in tension with the value inferred from the CMB and other higher redshift probes. In ref. [1], the authors proposed a rapid transition in the value of the effective Newtonian gravitational constant G in order to alleviate the Hubble tension. The transition point was chosen so as to only affect distance estimates to Hubble flow SNe. However, in this study, the authors made the assumption that SNe Ia peak luminosity $L$ increases with Chandrashekhar mass $M_c$. This hypothesis contradicts a previous semi-analytic study of SN light curves in the presence of G-transition [2] which found that $L\propto M_c^{-0.97}$. Motivated by the results of refs. [1] and [2], we propose a hypothesis of a sudden recent change in the effective G at an epoch which corresponds to a look-back distance between $\sim$ 7 - 80 Mpc. A transition in G at these distances would affect both our estimate of the distances to Cepheids in calibrator galaxies, as well as to the Hubble flow supernovae. Upon fitting the observational data to this hypothesis, we find three interesting results: (i) we find mild evidence for a G-transition at 22.4 Mpc (73 million years ago) which is preferred (using certain estimators) by the calibrator type Ia SNe data over no G-transition, (ii) the H0 parameter inferred under this hypothesis is in good agreement with the value obtained from the CMB for a 4% larger value of G at earlier times, thus potentially resolving the Hubble tension, (iii) we obtain a fit to the scaling relationship between SN peak luminosity $L$ and Chandrasekhar mass $M_c$, as $L\propto M_c^{-1.68 \pm 0.68}$, which is in good agreement with the prediction of the theoretical study of ref. [2]. We also discuss how other probes could be used to verify this transition in the value of G.

astro-ph.CO↗

arXiv2022

Star-forming S0 Galaxies in SDSS-MaNGA: fading spirals or rejuvenated S0s?

We investigate the origin of rare star-formation in an otherwise red-and-dead population of S0 galaxies using spatially resolved spectroscopy. Our sample consists of $120$ low redshift ($z<0.1$) star-forming S0 (SF-S0) galaxies from the SDSS-IV MaNGA DR15. We have selected this sample after a visual inspection of deep images from the DESI Legacy Imaging Surveys DR9 and the Subaru/HSC-SSP survey PDR3, to remove contamination from spiral galaxies. We also construct two control samples of star-forming spirals (SF-Sps) and quenched S0s (Q-S0s) to explore their evolutionary link with the star-forming S0s. To study star-formation at resolved scales, we use dust-corrected $H_α$ luminosity and stellar density ($Σ_\star$) maps to construct radial profiles of star-formation rate (SFR) surface density ($Σ_{SFR}$) and specific SFR (sSFR). Examining these radial profiles, we find that star-formation in SF-S0s is centrally dominated as opposed to disc dominated star-formation in spirals. We also compared various global (size-mass relation, bulge-to-total luminosity ratio) and local (central stellar velocity dispersion) properties of SF-S0s to those of the control sample galaxies. We find that SF-S0s are structurally similar to the quenched S0s and are different from star-forming spirals. We infer that SF-S0s are unlikely to be fading spirals. Inspecting stellar and gas velocity maps, we find that more than $50\%$ of the SF-S0 sample shows signs of recent galaxy interactions such as kinematic misalignment, counter-rotation, and unsettled kinematics. Based on these results, we conclude that in our sample of SF-S0s, star-formation has been rejuvenated, with minor mergers likely to be a major driver.

astro-ph.GA↗