EMU/GAMA: Understanding the link between dust geometry and star formation rate in galaxies

Abstract

We investigate the link between dust obscuration and star formation rate (SFR) estimators using Halpha luminosities, L_Halpha and radio luminosities, L_radio. While the Balmer Decrement (BD) is the standard tool for attenuating Halpha, it can fail to account for optically thick dust regions from which Halpha cannot escape. The ratio of SFRs estimated from radio luminosity and L_Halpha corrected for dust attenuation using the BD can be used as a probe of the degree of optically thick dust affecting Halpha. We explore this combining Evolutionary Map of the Universe (EMU) Early Science data at 887.5MHz in the Galaxy and Mass Assembly (GAMA) G23 field with the GAMA data. We draw on dust estimates using both the BD and the dust mass, M_d, demonstrating systematic underlying dependencies with L_radio/L_Halpha. By combining the BD and M_d, we quantify how they relate to L_radio/L_Halpha and other galaxy properties. We use this approach to establish an Halpha SFR (SFR_Halpha) estimator that accounts for optically thick dust, demonstrating its consistency with conventional SFR indicators. Rather than proposing a replacement for standard correction methods, we aim to demonstrate the effectiveness of a dust geometry model that integrates both BD and M_d parameters. This H_dust parameter provides a more physically complete representation of optically thick environments that traditional methods may overlook, and can produce SFR estimates consistent with traditional techniques.