GAMA/H-ATLAS: The ultraviolet spectral slope and obscuration in galaxies

TL;DR

This study compares various dust obscuration measures in galaxies using multiwavelength data, highlighting their inconsistencies and limitations, especially in high-redshift galaxy star formation rate estimations.

Contribution

It provides a comprehensive analysis of the relationships between UV spectral slope, Balmer decrement, and IR/FUV ratio, emphasizing their scatter and limitations in dust correction methods.

Findings

Large scatter between Balmer decrement and UV spectral slope.

FUV-based SFRs overestimate when using standard $eta$ corrections.

Neither UV slope nor IR/FUV ratio provides tight dust obscuration constraints.

Abstract

We use multiwavelength data from the Galaxy And Mass Assembly (GAMA) and Herschel ATLAS (H-ATLAS) surveys to compare the relationship between various dust obscuration measures in galaxies. We explore the connections between the ultraviolet (UV) spectral slope, $\beta$, the Balmer decrement, and the far infrared (IR) to $150\,$nm far ultraviolet (FUV) luminosity ratio. We explore trends with galaxy mass, star formation rate (SFR) and redshift in order to identify possible systematics in these various measures. We reiterate the finding of other authors that there is a large scatter between the Balmer decrement and the $\beta$ parameter, and that $\beta$ may be poorly constrained when derived from only two broad passbands in the UV. We also emphasise that FUV derived SFRs, corrected for dust obscuration using $\beta$, will be overestimated unless a modified relation between $\beta$ and the attenuation factor is used. Even in the optimum case, the resulting SFRs have a significant scatter, well over an order of magnitude. While there is a stronger correlation between the IR to FUV luminosity ratio and $\beta$ parameter than with the Balmer decrement, neither of these correlations are particularly tight, and dust corrections based on $\beta$ for high redshift galaxy SFRs must be treated with caution. We conclude with a description of the extent to which the different obscuration measures are consistent with each other as well as the effects of including other galactic properties on these correlations.