The Initial Mass Function in the Extended Ultraviolet Disk of M83

Sarah M. Bruzzese, David A. Thilker, Gerhardt Meurer, Luciana Bianchi, Adam B. Watts, Annette M. N. Ferguson, Armando Gil de Paz, Barry F. Madore, D. Christopher Martin, R. Michael Rich

Research output: Contribution to journalArticlepeer-review


Using Hubble Space Telescope ACS/WFC data we present the photometry and spatial distribution of resolved stellar populations of four fields within the extended ultraviolet disk (XUV disk) of M83. These observations show a clumpy distribution of main-sequence stars and a mostly smooth distribution of red giant branch stars. We constrain the upper-end of the initial mass function (IMF) in the outer disk using the detected population of main-sequence stars and an assumed constant star formation rate (SFR) over the last 300 Myr. By comparing the observed main-sequence luminosity function to simulations, we determine the best-fitting IMF to have a power law slope α=−2.35±0.3 and an upper-mass limit Mu=25+17−3M⊙. This IMF is consistent with the observed Hα emission, which we use to provide additional constraints on the IMF. We explore the influence of deviations from the constant SFR assumption, finding that our IMF conclusions are robust against all but strong recent variations in SFR, but these are excluded by causality arguments. These results, along with our similar studies of other nearby galaxies, indicate that some XUV disks are deficient in high-mass stars compared to a Kroupa IMF. There are over one hundred galaxies within 5 Mpc, many already observed with HST, thus allowing a more comprehensive investigation of the IMF, and how it varies, using the techniques developed here.
Original languageEnglish
Pages (from-to)2366-2390
Number of pages25
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Early online date22 Nov 2019
Publication statusPublished - 1 Jan 2020


  • astro-ph.GA


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