Non-parametric Triaxial Deprojection of Elliptical Galaxies

TL;DR

This paper introduces a non-parametric grid-based method to reconstruct the three-dimensional luminosity density of elliptical galaxies from surface brightness, accounting for triaxial shapes and viewing angle constraints.

Contribution

It presents a novel non-parametric deprojection technique that relaxes shape constraints and estimates galaxy orientations using photometric data alone.

Findings

Successfully reconstructs intrinsic triaxial densities in test models.

Can constrain galaxy viewing angles from photometry.

Demonstrates method on N-body simulation data.

Abstract

We present a grid-based non-parametric approach to obtain a triaxial three-dimensional luminosity density from its surface brightness distribution. Triaxial deprojection is highly degenerate and our approach illustrates the resulting difficulties. Fortunately, for massive elliptical galaxies, many deprojections for a particular line of sight can be discarded, because their projection along other lines of sight does not resemble elliptical galaxies. The near-elliptical isophotes of these objects imply near ellipsoidal intrinsic shapes. In fact, deprojection is unique for densities distributed on ellipsoidal shells. The constrained non-parametric deprojection method we present here relaxes this constraint and assumes that the contours of the luminosity density are boxy/discy ellipsoids with radially varying axis ratios. With this approach we are able to reconstruct the intrinsic triaxial densities of our test models, including one drawn from an $N$-body simulation. The method also allows to compare the relative likelihood of deprojections at different viewing angles. We show that the viewing orientations of individual galaxies with nearly ellipsoidal isophotal shapes can be constrained from photometric data alone.