Image Decomposition of Barred Galaxies and AGN Hosts

TL;DR

This study performs multi-component decomposition of galaxy images to analyze the structural properties of barred galaxies and AGN hosts, highlighting the importance of including bars and AGN in models for accurate measurements.

Contribution

It introduces a comprehensive method using BUDDA v2.1 for detailed galaxy decomposition, emphasizing the impact of bars and AGN on structural parameter estimation.

Findings

Neglecting bars can double the bulge-to-total luminosity ratio.

Reliable structural parameters can be obtained up to ~1.5 Kpc resolution.

Ignoring AGN light has minimal effect at low resolution.

Abstract

I present the results of multi-component decomposition of V and R broadband images of a sample of 17 nearby galaxies, most of them hosting bars and active galactic nuclei. I use BUDDA v2.1 to produce the fits, allowing to include bars and AGN in the models. A comparison with previous results from the literature shows a fairly good agreement. It is found that the axial ratio of bars, as measured from ellipse fits, can be severely underestimated if the galaxy axisymmetric component is relatively luminous. Thus, reliable bar axial ratios can only be determined by taking into account the contributions of bulge and disc to the light distribution in the galaxy image. Through a number of tests, I show that neglecting bars when modelling barred galaxies can result in a overestimation of the bulge-to-total luminosity ratio of a factor of two. Similar effects result when bright, type 1 AGN are not considered in the models. By artificially redshifting the images, I show that the structural parameters of more distant galaxies can in general be reliably retrieved through image fitting, at least up to the point where the physical spatial resolution is ~ 1.5 Kpc. This exercise shows that disc parameters are particularly robust, but bulge parameters are prone to errors if its effective radius is small compared to the seeing radius, and might suffer from systematic effects. In this low resolution regime, the effects of ignoring bars are still present, but AGN light is smeared out. I briefly discuss the consequences of these results to studies of the structural properties of galaxies, in particular on the stellar mass budget in the local universe. With reasonable assumptions, it is possible to show that the stellar content in bars can be similar to that in classical bulges and elliptical galaxies. (Abridged)