Predicting dust extinction properties of star-forming galaxies from H-alpha/UV ratio

TL;DR

This study develops an empirical method to predict dust extinction in star-forming galaxies using H-alpha/UV ratios, accounting for stellar mass and H-alpha equivalent width, improving accuracy when Balmer decrement data is unavailable.

Contribution

It introduces a new calibration combining H-alpha/UV ratio, stellar mass, and H-alpha equivalent width to better estimate dust extinction in galaxies, reducing systematic uncertainties.

Findings

H-alpha dust extinction correlates with H-alpha/UV ratio but shows scatter influenced by stellar mass and EW(Ha)

Higher mass galaxies exhibit more dust obscuration in nebular regions compared to stellar light

The new calibration reduces uncertainties in dust extinction estimates by 15-30%

Abstract

Using star-forming galaxies sample in the nearby Universe (0.02<z<0.10) selected from the SDSS (DR7) and GALEX all-sky survey (GR5), we present a new empirical calibration for predicting dust extinction of galaxies from H-alpha-to-FUV flux ratio. We find that the H-alpha dust extinction (A(Ha)) derived with H-alpha/H-beta ratio (Balmer decrement) increases with increasing H-alpha/UV ratio as expected, but there remains a considerable scatter around the relation, which is largely dependent on stellar mass and/or H-alpha equivalent width (EW(Ha)). At fixed H-alpha/UV ratio, galaxies with higher stellar mass (or galaxies with lower EW(Ha)) tend to be more highly obscured by dust. We quantify this trend and establish an empirical calibration for predicting A(Ha) with a combination of H-alpha/UV ratio, stellar mass and EW(Ha), with which we can successfully reduce the systematic uncertainties accompanying the simple H-alpha/UV approach by ~15-30%. The new recipes proposed in this study will provide a convenient tool for predicting dust extinction level of galaxies particularly when Balmer decrement is not available. By comparing A(Ha) (derived with Balmer decrement) and A(UV) (derived with IR/UV luminosity ratio) for a subsample of galaxies for which AKARI FIR photometry is available, we demonstrate that more massive galaxies tend to have higher extra extinction towards the nebular regions compared to the stellar continuum light. Considering recent studies reporting smaller extra extinction towards nebular regions for high-redshift galaxies, we argue that the dust geometry within high-redshift galaxies resemble more like low-mass galaxies in the nearby Universe.