Ultraviolet Imaging Telescope Observations of H{\small{II}} Regions in M74

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Session 43 -- HII Regions and Star Formation in Spirals
Display presentation, Thursday, January 13, 9:30-6:45, Salons I/II Room (Crystal Gateway)

[43.02] Ultraviolet Imaging Telescope Observations of H{\small{II}} Regions in M74

J.D. Offenberg, R.H. Cornett, K-P Cheng, M.R. Greason (Hughes STX), R.C. Bohlin (STScI), R.W. O'Connell (U Va), M.S. Roberts (NRAO), A.M. Smith, T.P. Stecher (GSFC/LASP)

M74 (NGC 628) is an ScI galaxy which is viewed nearly face-on with many well-defined \hii regions. We report individual UV fluxes of over 160 \hii regions in M74, as imaged by the Ultraviolet Imaging Telescope during the Astro-1 mission in December, 1990. We compare the \hii region fluxes in the near-UV (2490 \AA) and far-UV (1520 \AA) with each other and with the fluxes measured in the B, R and H$\alpha$ bands. Preliminary results indicate that emission from \hii regions directly contributes 30\% of all UV flux.

We also compare the locations and the morphologies of individual \hii emission features in the near-UV and H$\alpha$. The average displacement between an \hii region's near-UV emission peak and its H$\alpha$ emission peak is approximately 3 arcseconds and is measurably greater than the uncertainty which may be attributed to known sources of error. Because the UV image sources are generally reflection nebulae while the H$\alpha$ sources are ionized gas, this comparison gives valuable information about the relative locations of these two ISM components.

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