The Impact of Inclination-dependent Attenuation on Ultraviolet Star Formation Rate Tracers

TL;DR

This study shows that inclination significantly affects ultraviolet star formation rate tracers and proposes inclination-dependent corrections to improve the accuracy of SFR estimates in disk galaxies.

Contribution

It introduces new inclination-dependent relations for hybrid SFR estimators and the $A_{ m FUV}$-$eta$ relation, enhancing the precision of star formation rate measurements.

Findings

Inclination impacts hybrid SFR estimators and the $A_{ m FUV}$-$eta$ relation.

Inclination-dependent corrections reduce residual scatter by about a factor of 2.

Considering inclination improves the accuracy of SFR estimates in disk galaxies.

Abstract

We examine and quantify how hybrid (e.g., UV+IR) star formation rate (SFR) estimators and the $A_{\rm FUV}$-$\beta$ relation depend on inclination for disk-dominated galaxies using spectral energy distribution modeling that utilizes the inclination-dependent attenuation curves described in Doore et al. We perform this analysis on a sample of 133 disk-dominated galaxies from the CANDELS fields and 18 disk galaxies from the Spitzer Infrared Nearby Galaxies Survey and Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel samples. We find that both the hybrid SFR estimators and the $A_{\rm FUV}$-$\beta$ relation present clear dependencies on inclination. To quantify this dependence in the hybrid SFR estimators, we derive an inclination and a far-UV and near-IR color-dependent parametric relation for converting observed UV and IR luminosities into SFRs. For the $A_{\rm FUV}$-$\beta$ relation, we introduce an inclination-dependent component that accounts for the majority of the inclination dependence with the scatter of the relation increasing with inclination. We then compare both of these inclination-dependent relations to similar inclination-independent relations found in the literature. From this comparison, we find that the UV+IR correction factor and $A_{\rm FUV}$ for our hybrid and $A_{\rm FUV}$-$\beta$ relations, respectively, result in a reduction in the residual scatter of our sample by approximately a factor of 2. Therefore, we demonstrate that inclination must be considered in hybrid SFR estimators and the $A_{\rm FUV}$-$\beta$ relation to produce more accurate SFR estimates in disk-dominated galaxies.