Comparison of H-alpha and UV Star Formation Rates in the Local Volume: Systematic Discrepancies for Dwarf Galaxies

• Published in: arXiv.org 2009-09
• Main Authors: Lee, Janice C, Gil de Paz, Armando, Tremonti, Christy, Kennicutt, Robert C, Salim, Samir, Bothwell, Matthew, Calzetti, Daniela, Dalcanton, Julianne, Dale, Daniel, Engelbracht, Chad, Jose G Funes S J, Johnson, Benjamin, Sakai, Shoko, Skillman, Evan, Liese van Zee, Fabian, Walter, Weisz, Daniel
• Format: Article
• Language: English
• Subjects: Active galaxies; Attenuation; Consistency; Dwarf galaxies; Dwarf stars; Fluxes; Luminosity; Magellanic clouds; Massive stars; Narrowband; Nebulae; Spiral galaxies; Star & galaxy formation; Star formation; Sun; Surface brightness; Tracers
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.0909.5205

(abridged) Using a complete sample of ~300 star-forming galaxies within 11 Mpc, we evaluate the consistency between star formation rates (SFRs) inferred from the far ultraviolet (FUV) non-ionizing continuum and H-alpha nebular emission, assuming standard conversion recipes in which the SFR scales linearly with luminosity at a given wavelength. Our analysis probes SFRs over 5 orders of magnitude, down to ultra-low activities on the order of ~0.0001 M_sun/yr. The data are drawn from the 11 Mpc H-alpha and Ultraviolet Galaxy Survey (11HUGS), which has obtained H-alpha fluxes from ground-based narrowband imaging, and UV fluxes from imaging with GALEX. For normal spiral galaxies (SFR~1 M_sun/yr), our results are consistent with previous work which has shown that FUV SFRs tend to be lower than H-alpha SFRs before accounting for internal dust attenuation, but that there is relative consistency between the two tracers after proper corrections are applied. However, a puzzle is encountered at the faint end of the luminosity function. As lower luminosity dwarf galaxies, roughly less active than the Small Magellanic Cloud, are examined, H-alpha tends to increasingly under-predict the SFR relative to the FUV. Although past studies have suggested similar trends, this is the first time this effect is probed with a statistical sample for galaxies with SFR~