Candidate List of Edge-on Galaxies with Substantial Extraplanar Dust

TL;DR

This study identifies edge-on galaxies with significant extraplanar dust by fitting UV images with a radiative transfer model and analyzing the scale-height to diameter ratios.

Contribution

Introduces a method to classify galaxies based on extraplanar dust presence using radiative transfer modeling and scale-height analysis.

Findings

17 galaxies likely have substantial extraplanar dust.

6 galaxies likely have little extraplanar dust.

No strong dependence on UV surface brightness was found.

Abstract

We present a list of edge-on galaxies that might have substantial extraplanar dust. Twenty-three edge-on galaxies were selected as target galaxies from an edge-on galaxy catalog, and their Galaxy Evolution Explorer far-ultraviolet images were fitted with three dimensional radiative transfer galaxy model. The galaxy model is described by two disks: one for the light source and the other for the dust. The best-fit parameters were found by employing a global optimization method, called differential evolution. To find the galaxies with substantial extraplanar dust using the best-fit parameters, we plotted the ratio of scale-height to galactic diameter: $z_s/D_{25,ph}$ (light source) vs $z_d/D_{25,ph}$ (dust). We found that 17 and 6 galaxies fall on the region of $(z_s/D_{25,ph}\times100)>0.2$ and $(z_s/D_{25,ph}\times100)<0.2$, respectively. The former is named as "high-group" and the latter is named as "low-group." We conclude that "high-group" is likely to be the galaxies with substantial extraplanar dust, while "low-group" is likely to be the ones with little extraplanar dust, i.e. typical galactic thin disk, based on the following points: (1) the relative positions of "high-group" and "low-group" on the plot $z_s/D_{25,ph}$ vs $z_d/D_{25,ph}$ with respect to the reference values from optical radiative transfer studies; (2) the lower scale-height of the young stellar population than the old stellar population; and (3) a test result that shows the existence of extraplanar dust makes $z_s$ and $z_d$ overestimated in the fitting results. We also examined the dependence of the group separation on the surface density of far-ultraviolet luminosity ($L_{FUV}/D^2_{25,ph}$), but found no strong dependence.