J/ApJ/438/181 Observations of H II Regions in M81 (Hill+ 1995)
Ultraviolet Imaging Telescope and Optical Emission-Line Observations of H II
Regions in M81
Hill J.K., Cheng K.-P., Bohlin R.C., Cornett R.H., Hintzen P.M.N.,
Robert M.S., O'Connell R.W., Roberts M.S.,Smith A.M., Smith E.P.,
Stecher T.P.
<Astrophys. J. 438, 181 (1995)>
=1995ApJ...438..181H 1995ApJ...438..181H
ADC_Keywords: H II regions ; Ultraviolet ;
Keywords: dust, extinction - galaxies: individual (M81) -
galaxies: stellar content - H II regions - ultraviolet: galaxies
Abstract:
Images of the type Sab spiral galaxy M81 were obtained in far-UV and
near-UV bands by the Ultraviolet Imaging Telescope (UIT) during the
Astro-1 Spacelab mission of 1990 December. Magnitudes in the two UV
bands are determined for 52 H II regions from the catalog of Petit,
Sivan, & Karachentsev (1988A&AS...74..475P 1988A&AS...74..475P). Fluxes of the H-alpha and
H-beta emission lines are determined from CCD images. Extinctions for
the brightest H II regions are determined from observed Balmer
decrements. Fainter H II regions are assigned the average of published
radio-H-alpha extinctions for several bright H II regions. The
radiative transfer models of Witt, Thronson, & Capuano (1992, ApJ,
393, 611) are shown to predict a relationship between Balmer Decrement
and H-alpha extinction consistent with observed line and radio fluxes
for the brightest 7 H II regions and are used to estimate the UV
extinction. Ratios of Lyman continuum flux (computed from the
extinction corrected H-alpha flux) to the extinction corrected far-UV
flux are compared with ratios predicted by model spectra computed for
IMF slope equal to -1.0 and stellar masses ranging from 5 to 120 Msun.
Ages and masses are estimated by comparing the H-alpha and far-UV
fluxes and their ratio with the models. The total of the estimated
stellar masses for the 52 H II regions is 1.4x105 Msun. The
star-formation rate inferred for M81 from the observed UV and H-alpha
fluxes is low for a spiral galaxy at ∼0.13 Msun/yr, but consistent
with the low star-formation rates obtained by Kennicutt
(1983ApJ...272...54K 1983ApJ...272...54K) and Caldwell et al. (1991ApJ...370..526C 1991ApJ...370..526C) for
early-type spirals.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 47 52 M81 H II region photometry
table2.tex 71 109 LaTeX version of Table 2
aastab.sty 72 115 Modified AAS table style file
environ.tex 77 125 Custom LaTeX environments and related macros
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- PSK *H II region number from PSK
4- 9 F6.2 mag m152 Far-UV magnitude
10-14 F5.2 mag e_m152 Estimated error in m152
15-20 F6.2 mag m249 Near-UV magnitude
21-25 F5.2 mag e_m249 Estimated error in m249
26-31 F6.2 10-14mW/m2 fHa H-alpha flux
32-36 F5.2 10-14mW/m2 e_fHa Estimated fractional error in fHa
37-42 F6.2 10-14mW/m2 fHb *[]?=0.0 H-beta flux
43-47 F5.2 10-14mW/m2 e_fHb *[]?=0.0 Estimated fractional error in fHb
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Note on PSK:
H II region number from Petit, Sivan, & Karachentsev (1988A&AS...74..475P 1988A&AS...74..475P)
Note on fHb, e_fHb:
For 11 H II regions not measurable in the H-beta line, the H-beta
fluxes and the corresponding errors are both set to 0.0.
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Origin: AAS CD-ROM series, Volume 4, 1995 Lee Brotzman [ADS] 06-May-1995
(End) [CDS] 11-Jul-1995