Deprojection of external barred galaxies from photometry

TL;DR

This paper introduces a method to reconstruct the three-dimensional density distribution of barred galaxies from two-dimensional photometric images, validated with mock data, aiding in galactic dynamical modeling.

Contribution

The authors develop a novel deprojection technique for barred galaxies that separates bulge and disk components and considers the bar's triaxial shape, improving 3D density reconstruction.

Findings

The method recovers the 3D density of disk and inner barred bulge regions.

Orbit integrations show 85% similarity between model-inferred and true potentials.

Supports the formation of boxy/peanut-shaped structures and elongated bars.

Abstract

The observations of external galaxies are projected to the 2D sky plane. Reconstructing the 3D intrinsic density distribution of a galaxy from the 2D image is challenging, especially for barred galaxies, but is a critical step for constructing galactic dynamical models. Here we present a method for deprojecting barred galaxies and we validate the method by testing against mock images created from an N-body simulation with a peanut-shaped bar. We decompose a galaxy image into a bulge (including a bar) and a disk. By subtracting the disk from the original image a barred bulge remains. We perform multi-Gaussian expansion (MGE) fit to each component, then we deproject them separately by considering the barred bulge is triaxial while the disk is axisymmetric. We restrict the barred bulge to be aligned in the disk plane and has a similar thickness to the disk in the outer regions. The 3D density distribution is thus constructed by combining the barred bulge and the disk. Our model can generally recover the 3D density distribution of disk and inner barred bulge regions, although not a perfect match to the peanut-shaped structure. By using the same initial conditions, we integrate the orbits in our model-inferred potential and the true potential by freezing the N-body simulation. We find that 85% of all these orbits have similar morphologies in these two potentials, and our model supports the orbits that generate a boxy/peanut-shaped structure and an elongated bar similar to these in the true potential.