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UV Colors and Extinctions of HII Regions in the Whirlpool Galaxy (M51) | | Hill
; Jesse K. ; Waller
; William H. ; Cornett
; Robert H. ; Bohlin
; Ralph C. ; Cheng
; K.-P. ; Neff
; Susan G. ; O’Connell
; Robert W. ; Roberts
; Morton S. ; Smith
; Andrew M. ; Hintzen
; P.M.N. ; Smith
; Eric P. ;
; Stecher
; Theodore P.
; | | Date: |
27 Jun 1996 | | Subject: | astro-ph | | Affiliation: | 1 and 5); Waller, William H. (1 and 5); Cornett, Robert H. (1 and 5); Bohlin, Ralph C. ; Cheng, K.-P. ; Neff, Susan G. ; O’Connell, Robert W. ; Roberts, Morton S. ; Smith, Andrew M. ; Hintzen, P.M.N. (5 and 6); Smith, Eric P. ; and Stecher, Theod | | Abstract: | Far-UV (1520 ang.), U, H-alpha, and R images of the interacting Sbc spiral galaxy M51 were obtained by the Ultraviolet Imaging Telescope (UIT) and at Mt. Laguna Observatory. The mu(152)-mu(U) radial gradient of >1 mag, becoming bluer with increasing radius, is attributed primarily to a corresponding radial extinction gradient. Magnitudes in both UV bands and H-alpha fluxes are reported for 28 HII regions. Optical extinctions for the 28 corresponding UV sources are computed from the measured m(152)-U colors by fitting to the optical extinctions of Nakai and Kuno (1995). The normalized far-UV extinction A(152)/E(B-V) increases with radius or decreasing metallicity, from 5.99 to 6.54, compared with the Galactic value 8.33. The best-fit m(152)-U color for no extinction, -3.07, is the color of a model solar metallicity starburst of age ~2.5 Myr with IMF slope -1.0. HII regions show decreasing observed H-alpha fluxes with decreasing radius, relative to the H-alpha fluxes predicted from the observed f(152) for age 2.5 Myr, after correction for extinction. We attribute the increasing fraction of ``missing’’ H-alpha flux with decreasing radius to increasing extinction in the Lyman continuum. Increasing extinction-corrected far-UV flux of the HII regions with decreasing radius is probably a result of the corresponding increasing column density of the interstellar gas resulting in larger mass OB associations. The estimated dust-absorbed Lyman continuum flux is ~0.6 times the far-infrared energy flux of M51 observed by IRAS. | | Source: | arXiv, astro-ph/9606168 | | Services: | Forum | Review | PDF | Favorites | |
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