University of Minnesota
School of Physics & Astronomy

Physics and Astronomy Calendar

Monday, November 3rd 2014
12:15 pm:
Speaker: Kristy McQuinn, University of Minnesota
Subject: Are We Correctly Measuring the Star Formation in Galaxies?

Integrating our knowledge of star formation traced by observations at different wavelengths is essential for correctly interpreting star formation activity and galaxy evolution in a variety of systems and environments. In this talk, I will compare extinction corrected integrated ultraviolet (UV) emission from resolved galaxies with star formation histories (SFHs) derived from resolved stellar populations and color-magnitude diagram (CMD) fitting techniques in 19 nearby starburst and post-starburst dwarf galaxies. The datasets are from the panchromatic STARBurst IRregular Dwarf Survey (STARBIRDS) and include deep legacy GALEX UV imaging, HST optical imaging, and Spitzer MIPS imaging. For the majority of the sample, the integrated far ultraviolet (FUV) fluxes predicted from the CMD based SFHs generally agree with the measured integrated FUV fluxes from GALEX images after correcting for extinction based on the mid-infrared emission in the MIPS images. The agreement between predictions from three different models and observations indicates that (1) the UV attenuation has been adequately corrected using the infrared flux from the MIPS images, (2) the star formation rates (SFRs) are not heavily affected by stochastic effects, and (3) stellar evolution models are correctly modeling the optical to UV fluxes at recent times. Despite being able to model the fluxes correctly, there is a systematic deviation between the SFRs based on integrated FUV luminosities and existing scaling relations, and the SFRs based on the resolved stellar populations. This offset is not driven by different star formation timescales, variations in SFHs, nor UV attenuation. While stochastic changes in the SFRs on short timescales (t<20 Myr) are a contributing factor to the dispersion in the measurements, temporal sampling of the SFHs is not the dominant driver of the discrepancy. This first comparison between CMD-based SFHs and an integrated FUV emission SFR indicator suggest that the FUV-SFR scaling relation calibrated to higher-SFR galaxies does not accurately reproduce the star formation activity in dwarf galaxies. We present an empirical calibration of the FUV SFR relation for dwarf galaxies which is ~2 times larger than previous relations and provide a guide for applying FUV-SFR scaling relations in studies of unresolved, high-redshift galaxies.

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