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Date and Time of the Query: 2019-04-24 T03:18:45 PDT
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For refcode 2012ApJ...744...44W:
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2012ApJ...744...44W Modeling the Effects of Star Formation Histories on H{alpha} and Ultraviolet Fluxes in nearby Dwarf Galaxies Weisz, Daniel R.; Johnson, Benjamin D.; Johnson, L. Clifton; Skillman, Evan D.; Lee, Janice C.; Kennicutt, Robert C.; Calzetti, Daniela; van Zee, Liese; Bothwell, Matthew S.; Dalcanton, Julianne J.; Dale, Daniel A.; Williams, Benjamin F. Abstract. We consider the effects of non-constant star formation histories (SFHs) on H{alpha} and GALEX far-ultraviolet (FUV) star formation rate (SFR) indicators. Under the assumption of a fully populated Chabrier initial mass function (IMF), we compare the distribution of H{alpha}-to-FUV flux ratios from ~1500 simple, periodic model SFHs with observations of 185 galaxies from the Spitzer Local Volume Legacy survey. We find a set of SFH models that are well matched to the data, such that more massive galaxies are best characterized by nearly constant SFHs, while low-mass systems experience burst amplitudes of ~30 (i.e., an increase in the SFR by a factor of 30 over the SFR during the inter-burst period), burst durations of tens of Myr, and periods of ~250 Myr these SFHs are broadly consistent with the increased stochastic star formation expected in systems with lower SFRs. We analyze the predicted temporal evolution of galaxy stellar mass, R-band surface brightness, H{alpha}-derived SFR, and blue luminosity, and find that they provide a reasonable match to observed flux distributions. We find that our model SFHs are generally able to reproduce both the observed systematic decline and increased scatter in H{alpha}-to-FUV ratios toward low-mass systems, without invoking other physical mechanisms. We also compare our predictions with those from the Integrated Galactic IMF theory with a constant SFR. We find that while both predict a systematic decline in the observed ratios, only the time variable SFH models are capable of producing the observed population of low-mass galaxies (M_*_ <~ 10^7^ M_sun_) with normal H{alpha}-to-FUV ratios. These results demonstrate that a variable IMF alone has difficulty explaining the observed scatter in the H{alpha}-to-FUV ratios. We conclude by considering the limitations of the model SFHs and discuss the use of additional empirical constraints to improve future SFH modeling efforts. Key words: galaxies: dwarf, galaxies: evolution, galaxies: formation, galaxies: star formation
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