Using detailed analysis methods we have examined the stellar populations in the Local Group Galaxy M33 using resolved HST UV to V photometry, integrated resolved GALEX UV photometry, ancillary ground-based UBV stellar photometry and Hα imaging. We focused our work on young stellar populations (age < 30 million years) in OB associations in M33. The goal of our work was to calibrate the properties (age, mass, star formation rate) of OB associations in M33 derived from integrated GALEX UV photometry (as opposed to deriving them from photometry of the stars within the association) and thus calibrate GALEX measures of the recent star formation indicators in M33. This sought-for calibration is meant as a benchmark for more distant galaxies, for which, as opposed to M33, only unresolved data is available. In order make this calibration, OB associations masses and ages derived from GALEX photometry were compared to values obtained from analysis of resolved HST photometry. A secondary calibration was obtained by comparing GALEX FUV SFR of individual OB associations to SFR rates calculated in this work from Hα fluxes. We also compared global GALEX SFR measures to published integrated FIR and Hα SFR values for M33. The calibration of ages, masses and star formation rates is valid only if we use LMC2 type dust to correct the GALEX FUV and NUV magnitudes for extinction. Under this assumption, we obtain integrated star formation rates of ≈ 0.2 [special characters omitted] yr−1 for the recent (age < 108) yr, a good match for values cited in the literature. Besides this results, we performed a general analysis of the OB association properties as derived from GALEX and HST data. We derive the slopes of bright end of the OB association luminosity function and high mass end of the mass function and a value of ≈ −1.9 for either. We explore the radial mass distribution of OB associations in M33 and find it similar to that of Giant Molecular Clouds in M33. We also explore the difference between the LF of massive stars detected inside and outside the OB associations and find no difference in the slope at the bright end (slope = −0.58±0.06).
|Advisor:||Bianchi, Luciana, Kuntz, Kip D.|
|School:||The Johns Hopkins University|
|School Location:||United States -- Maryland|
|Source:||DAI-B 69/12, Dissertation Abstracts International|
|Keywords:||GALEX UV photometry, M33, Stellar populations|
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