Characterizing Dust Attenuation in Local Star Forming Galaxies: Inclination Effects and the 2175\AA\ Feature

TL;DR

This study investigates how galaxy inclination affects dust attenuation curves in local star-forming galaxies, revealing inclination-dependent UV features and implications for dust composition and distribution.

Contribution

It provides the first detailed analysis of inclination effects on dust attenuation curves and the 2175Å feature in a large galaxy sample, using multi-wavelength data.

Findings

Attenuation curves are shallower at UV wavelengths with increasing inclination.

A NUV excess suggests a 2175Å feature in high-inclination galaxies.

Differential reddening decreases with inclination.

Abstract

We characterize the influence that inclination has on the shape and normalization in average dust attenuation curves derived from a sample of ~10,000 local star-forming galaxies. To do this we utilize aperture-matched multi-wavelength data from the Galaxy Evolution Explorer, the Sloan Digital Sky Survey, the United Kingdom Infrared Telescope, and the Two Micron All-Sky Survey. We separate our sample into groups according to axial ratio (b/a) and obtain an estimate of their average total-to-selective attenuation $k(\lambda)$. The attenuation curves are found to be shallower at UV wavelengths with increasing inclination, whereas the shape at longer wavelengths remains unchanged. The highest inclination subpopulation (b/a<0.42) exhibits a NUV excess in its average selective attenuation, which, if interpreted as a 2175\AA\ feature, is best fit with a bump strength of 17-26% of the MW value. No excess is apparent in the average attenuation curve of lower inclination galaxies. The differential reddening between the stellar continuum and ionized gas is found to decrease with increasing inclination. We find that higher inclination galaxies have slightly higher values of $R_V$, although this is poorly constrained given the uncertainties. We outline possible explanations for these trends within a two component dust model (dense cloud+diffuse dust) and find that they can be naturally explained if carriers of the 2175\AA\ feature are preferentially destroyed in star-forming regions (UV-bright regions).