Non-parametric Deprojection of Surface Brightness Profiles of Galaxies in Generalised Geometries

TL;DR

This paper introduces DOPING, a Bayesian non-parametric algorithm for 3D deprojection of galaxy surface brightness profiles in complex geometries, accounting for shape variations with radius using MCMC optimization.

Contribution

The paper presents a novel deprojection method that handles generalised galaxy geometries and shape changes, improving accuracy over traditional parametric approaches.

Findings

Successfully tested on galaxies with varying morphologies

Applied to dwarf elliptical galaxies and X-ray cluster images

Demonstrated effective shape and density recovery

Abstract

We present a new Bayesian non-parametric deprojection algorithm DOPING (Deprojection of Observed Photometry using and INverse Gambit), that is designed to extract 3-D luminosity density distributions $\rho$ from observed surface brightness maps $I$, in generalised geometries, while taking into account changes in intrinsic shape with radius, using a penalised likelihood approach and an MCMC optimiser. We provide the most likely solution to the integral equation that represents deprojection of the measured $I$ to $\rho$. In order to keep the solution modular, we choose to express $\rho$ as a function of the line-of-sight (LOS) coordinate $z$. We calculate the extent of the system along the ${\bf z}$-axis, for a given point on the image that lies within an identified isophotal annulus. The extent along the LOS is binned and density is held a constant over each such $z$-bin. The code begins with a seed density and at the beginning of an iterative step, the trial $\rho$ is updated. Comparison of the projection of the current choice of $\rho$ and the observed $I$ defines the likelihood function (which is supplemented by Laplacian regularisation), the maximal region of which is sought by the optimiser (Metropolis Hastings). The algorithm is successfully tested on a set of test galaxies, the morphology of which ranges from an elliptical galaxy with varying eccentricity to an infinitesimally thin disk galaxy marked by an abruptly varying eccentricity profile. Applications are made to faint dwarf elliptical galaxy Ic~3019 and another dwarf elliptical that is characterised by a central spheroidal nuclear component superimposed upon a more extended flattened component. The result of deprojection of the X-ray image of triaxial cluster A1413 is also presented.