Hα, far-infrared and thermal radio continuum emission within the late-type spiral galaxy M33

Nicholas A. Devereux, Neb Duric, Paul Scowen

Research output: Contribution to journalArticle

33 Scopus citations

Abstract

New Hα imaging observations have revealed the morphology of the emission line gas and permitted the first measurement of the total Hα luminosity for the late-type spiral galaxy M33. The total Hα luminosity of M33 is (7.06±1.40) × 106 L and is dominated by emission from H II regions. The Hα image is compared with 6 and 20 cm thermal radio continuum images in order to quantify the extinction to H II regions in M33. The extinction is found to be high locally, but low globally. The extinction to the high surface brightness cores of H II regions corresponds to Aυ∼1 mag on average with no systematic dependence on radius. However, the extinction correction to the global Hα flux is much lower with Aυ∼0.0-0.4 mag. The difference suggests that the extinction is virtually negligible to the low surface brightness Hα emission outside the high surface brightness cores of H II regions. The Hα image is compared with a high-resolution far-infrared image, obtained with the Infrared Astronomical Satellite (IRAS), in order to constrain the contribution of O and B stars to the far-infrared luminosity of M33. The correspondence between the Hα and far-infrared morphology is striking when both images are convolved to a common resolution of 105 arcsec. The far-infrared luminosity, L(FIR), and the Hα luminosity, L(Hα), have been measured at 840 independent locations within M33 and the histogram of L(FIR)/L(Hα) ratios is remarkably similar to that determined for Galactic H II regions. Approximately 70% of the far-infrared luminosity of M33 is radiated by dust with temperatures greater than expected for cirrus, but similar to the temperatures measured by IRAS for Galactic and extragalactic H II regions. The results indicate that the majority (≥70%) of the far infrared and Hα luminosity of M33 is produced by massive stars.

Original languageEnglish (US)
Pages (from-to)236-248
Number of pages13
JournalAstronomical Journal
Volume113
Issue number1
DOIs
StatePublished - Jan 1997

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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