The GMRT archive atomic gas survey -- III. Comparative Study of Dark Matter Halos in Nearby Galaxies

TL;DR

This study tackles the cusp-core problem by comparing four dark matter halo profiles—NFW, Einasto, Burkert, and pISO—across 11 GARCIA galaxies using robust 3D kinematic rotation curves and MCMC mass modelling. It combines baryonic components (stars via $M/L$ from MGE+JAM and gas from HI) with dark matter to derive rotation curves, and also constructs non-parametric DM densities by subtracting baryonic contributions. The analysis shows outer DM profiles converge across models, while inner regions favour a cuspy NFW-like distribution, with the parametric and non-parametric approaches in reasonable agreement overall; the concentration parameter remains sensitive to the assumed inner profile. The work demonstrates the value of high-quality 3D kinematics for constraining inner halo structure and sets the stage for a larger GARCIA sample to refine the cusp-core issue and the stellar-to-halo mass relation.

Abstract

The distribution of dark matter in the inner regions of galaxies poses a key challenge for small-scale ΛCDM cosmology. While cold dark matter simulations predict cuspy inner density profiles, observations of low surface brightness (LSB) and dwarf galaxies often favour cored profiles, an issue known as the cusp-core problem. We investigate this problem by comparing four dark matter halo profiles: NFW (cuspy), Einasto (intermediate), Burkert (cored), and pseudo-isothermal (pISO) (cored) in a pilot sample of $11$ galaxies from the GMRT archive atomic gas survey (GARCIA). We have performed mass modelling using Markov Chain Monte Carlo (MCMC) techniques, utilising rotation curves derived from robust 3D Kinematic modelling. Baryonic contributions from stars derived using stellar kinematics based on $3.6μ\mathrm{m}$ or $r$-band photometry via Multi-Gaussian Expansion (MGE) combined with Jeans Anisotropic Model (JAM) and from gas, calculated directly from the gas surface density (HI + He) without assuming any predefined functional form, are included. Our mass modelling shows that all halo profiles provide statistically good fits, yielding consistent estimates of halo mass and stellar mass-to-light ratio. To validate our analysis, we examine the stellar-to-halo mass relation and find broad agreement with empirical models. Non-parametric density profiles derived from baryon-subtracted rotation curves show that NFW fits the inner regions best, while all profiles converge in the outskirts. Future studies with a larger sample from GARCIA will be helpful in refining this trend and addressing the cusp-core issue in greater depth.

Figures (5)

• Figure 4: Scaled the circular velocity contribution of the dark halo component for parametric and non-parametric dark matter. The dashed line corresponds to parametric dark matter using MCMC-based mass modelling, and each panel represents a different dark matter halo model, with different colours indicating different galaxies.
• Figure 5: Scaled dark matter density profiles: parametric (dashed lines; see Section \ref{['subsubsec: parametric dm']}) and non-parametric (circles; see Section \ref{['subsubsec:non para dm']}). Each panel corresponds to a different dark matter halo model, with different colours representing different galaxies.
• Figure 6: The $M_{\mathrm{star}}$–$M_{200}$ relation is shown for different dark matter halo profiles. In each figure, the left panel displays galaxies colour-coded by Hubble type, while the right panel shows the same galaxies colour-coded by the presence or absence of bars. Circle and square symbols denote galaxies from the https://physics.iisc.ac.in/ nroy/garcia_web/about.html sample, whereas dots represent galaxies from the https://astroweb.cwru.edu/SPARC/ database. Stars represent the galaxies from 2025AA...699A.311M: teal stars correspond to massive spirals, grey stars to dwarf galaxies, and pink stars to baryon-deficient dwarfs (BDDs). The black solid line indicates the relation from 2013MNRAS.428.3121M, and the yellow shaded region shows the corresponding $3\sigma$ uncertainty.
• Figure A1: Scaled dark matter density profiles: parametric (dashed lines; see Section \ref{['subsubsec: parametric dm']}) and non-parametric (circles; see Section \ref{['subsubsec:non para dm']}). Each panel corresponds to a different dark matter halo model, with different colours representing different galaxies.
• Figure B1: Comparison of single-$M/L$ (left) and bulge+disc $M/L$ (right) mass models for NGC4068; the upper panels show the modelled rotation curves and data, while the lower panels show the posterior distributions of the fitted parameters.