Total mass distributions of Sersic galaxies from photometry $&$ cent ral velocity dispersion

We develop a novel way of finding total mass density profiles in Sersic ellipticals, to about 3 times the major axis effective radius, using no other information other than what is typically available for distant galaxies, namely the observed surface brightness distribution and the central velocity dispersion $\sigma_0$. The luminosity density profile of the observed galaxy is extracted by deprojecting the measured brightness distribution and scaling it by a fiduciary, step-function shaped, $raw$ mass-to-light ratio profile ($M/L$). The resulting raw, discontinuous, total, 3-D mass density profile is then smoothed according to a proposed smoothing prescription. The parameters of this raw $M/L$ are characterised by implementing the observables in a model-based study. The complete characterisation of the formalism is provided as a function of the measurements of the brightness distribution and $\sigma_0$. The formalism, thus specified, is demonstrated to yield the mass density profiles of a suite of test galaxies and is successfully applied to extract the gravitational mass distribution in NGC 3379 and NGC 4499, out to about 3 effective radii.

💡 Research Summary

The paper introduces a novel, observationally economical technique for reconstructing the three‑dimensional total mass density profiles of elliptical galaxies that follow a Sérsic surface‑brightness law. Traditional mass‑modeling approaches for distant early‑type galaxies typically require extensive kinematic data (e.g., spatially resolved velocity dispersion profiles, higher‑order moments, or integral‑field spectroscopy) in addition to photometry. By contrast, the authors demonstrate that the combination of a galaxy’s surface‑brightness distribution and its central line‑of‑sight velocity dispersion (σ₀) is sufficient to recover the mass profile out to roughly three effective radii (≈ 3 Rₑ).

The method proceeds in four logical steps. First, the observed 2‑D surface brightness I(R) is fitted with a Sérsic function I(R)=I₀ exp