Predictions for the intrinsic UV continuum properties of star forming galaxies and the implications for inferring dust extinction

TL;DR

This study uses galaxy formation models to analyze the intrinsic UV continuum slopes of star-forming galaxies, revealing their variability and correlations with galaxy properties, which impacts dust extinction estimates.

Contribution

It provides the first detailed prediction of the intrinsic UV slopes distribution and their dependencies, improving the interpretation of dust attenuation in galaxies.

Findings

Intrinsic UV slope distribution has a standard deviation of 0.30 in beta.

Intrinsic UV slope correlates with star formation rate, luminosity, stellar mass, and redshift.

Uncertainty in UV attenuation estimates is about 0.7 magnitudes for individual galaxies.

Abstract

The observed ultraviolet continuum (UVC) slope is potentially a powerful diagnostic of dust obscuration in star forming galaxies. However, the intrinsic slope is also sensitive to the form of the stellar initial mass function (IMF) and to the recent star formation and metal enrichment histories of a galaxy. Using the galform semi-analytical model of galaxy formation, we investigate the intrinsic distribution of UVC slopes. For star-forming galaxies, we find that the intrinsic distribution of UVC slopes at z=0, parameterised by the power law index beta, has a standard deviation of sigma_beta=0.30. This suggests an uncertainty on the inferred UV attenuation of A_fuv=0.7$ (assuming a Calzetti attenuation curve) for an individual object, even with perfect photometry. Furthermore, we find that the intrinsic UVC slope correlates with star formation rate, intrinsic UV luminosity, stellar mass and redshift. These correlations have implications for the interpretation of trends in the observed UVC slope with these quantities irrespective of the sample size or quality of the photometry. Our results suggest that in some cases the attenuation by dust has been incorrectly estimated.