Dust-Corrected Star Formation Rates of Galaxies. I. Combinations of H-alpha and Infrared Tracers

TL;DR

This study combines H-alpha and infrared data to accurately measure star formation rates in galaxies, accounting for dust attenuation, and evaluates various methods for robust SFR estimation across different galaxy types.

Contribution

It extends a dust correction methodology from HII regions to entire galaxies, demonstrating the effectiveness of combined H-alpha and IR measurements for SFR estimation.

Findings

Composite H-alpha+IR SFRs agree with spectrophotometry-based rates

H-alpha combined with 24μm and 8μm luminosities are nearly as effective

Calibrations differ from HII region results due to evolved stellar populations

Abstract

We combine H-alpha emission-line and infrared continuum measurements of two samples of nearby galaxies to derive dust attenuation-corrected star formation rates (SFRs). We use a simple energy balance based method that has been applied previously to HII regions in the Spitzer Infrared Nearby Galaxies Survey (SINGS), and extend the methodology to integrated measurements of galaxies. We find that our composite H-alpha+IR based SFRs are in excellent agreement with attenuation-corrected SFRs derived from integrated spectrophotometry, over the full range of SFRs (0.01 -- 80 solar mass per year) and attenuations (0 -- 2.5 mag) studied. We find that the combination of H-alpha and total infrared luminosities provides the most robust SFR measurements, but combinations of H-alpha measurements with monochromatic luminosities at 24 micron and 8 micron perform nearly as well. The calibrations differ significantly from those obtained for HII regions (Calzetti et al. 2007), with the difference attributable to a more evolved population of stars heating the dust. Our results are consistent with a significant component of diffuse dust (the `IR cirrus' component) that is heated by a non-star-forming population. The same methodology can be applied to [OII]$\lambda$3727 emission-line measurements, and the radio continuum fluxes of galaxies can be applied in place of IR fluxes when the latter are not available. We assess the precision and systematic reliability of all of these composite methods.