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

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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
StatePublished - Jan 1 1997

Fingerprint

spiral galaxies
H II regions
luminosity
radio
continuums
extinction
astronomical satellites
brightness
O stars
B stars
cirrus
histogram
massive stars
histograms
dust
temperature
radii
high resolution
gases
gas

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Hα, far-infrared and thermal radio continuum emission within the late-type spiral galaxy M33. / Devereux, Nicholas A.; Duric, Neb; Scowen, Paul.

In: Astronomical Journal, Vol. 113, No. 1, 01.01.1997, p. 236-248.

Research output: Contribution to journalArticle

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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.",
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