Nebular and Stellar Dust Extinction Across the Disk of Emission-Line Galaxies on Small (KPC) Scales

TL;DR

This study maps and compares stellar and nebular dust extinction on small scales within star-forming galaxies at z~0.4, revealing how dust distribution relates to galaxy properties like mass and inclination.

Contribution

It provides the first resolved, pixel-by-pixel analysis of dust extinction in galaxies at this redshift, linking dust properties to galaxy structure and inclination effects.

Findings

Nebular to stellar dust extinction ratio exceeds unity but shows no trend with mass or SFR.

Inclination significantly influences the nebular to stellar extinction ratio.

Stellar dust extinction peaks at galaxy centers, but nebular extinction trends vary with galaxy mass.

Abstract

We investigate resolved kpc-scale stellar and nebular dust distribution in eight star-forming galaxies at z~0.4 in the GOODS fields. Constructing the observed Spectral Energy Distributions (SEDs) per pixel, based on seven bands photometric data from HST/ACS and WFC3, we performed pixel-by-pixel SED fits to population synthesis models and estimated small-scale distribution of stellar dust extinction. We use Halpha / Hbeta nebular emission line ratios from Keck/DEIMOS high resolution spectra at each spatial resolution element to measure the amount of attenuation faced by ionized gas at different radii from the center of galaxies. We find a good agreement between the integrated and median of resolved color excess measurements in our galaxies. The ratio of integrated nebular to stellar dust extinction is always greater than unity, but does not show any trend with stellar mass or star formation rate. We find that inclination plays an important role in the variation of the nebular to stellar excess ratio. The stellar color excess profiles are found to have higher values at the center compared to outer parts of the disk. However, for lower mass galaxies, a similar trend is not found for the nebular color excess. We find that the nebular color excess increases with stellar mass surface density. This explains the absence of radial trend in the nebular color excess in lower mass galaxies which lack a large radial variation of stellar mass surface density. Using standard conversions of star formation rate surface density to gas mass surface density, and the relation between dust mass surface density and color excess, we find no significant variation in the dust to gas ratio in regions with high gas mass surface densities, over the scales probed in this study.