CHAOS VIII: Far-Ultraviolet Spectra of M101 and The Impact of Wolf-Rayet Stars
The Astrophysical Journal(2024)
摘要
We investigate the stellar and nebular properties of 9 H II regions in the
spiral galaxy M101 with far-ultraviolet (FUV; 900-2000 Å) and optical
( 3200-10000 Å) spectra. We detect significant C III] 1907,1909 nebular
emission in 7 regions, but O III] 1666 only in the lowest-metallicity region.
We produce new analytic functions of the carbon ICF as a function of
metallicity in order to perform a preliminary C/O abundance analysis. The FUV
spectra also contain numerous stellar emission and P-Cygni features that we fit
with luminosity-weighted combinations of single-burst Starburst99 and BPASS
models. We find that the best-fit Starburst99 models closely match the observed
very-high-ionization P-Cygni features, requiring very-hot, young ( < 3 Myr),
metal-enriched massive stars. The youngest stellar populations are strongly
correlated with broad He II emission, nitrogen Wolf-Rayet (WR) FUV and optical
spectral features, and enhanced N/O gas abundances. Thus, the short-lived WR
phase may be driving excess emission in several N P-Cygni wind features (955
Å, 991 Å, 1720 Å) that bias the stellar continuum fits to higher
metallicities relative to the gas-phase metallicities. Accurate
characterization of these H II regions requires additional inclusion of WR
stars in the stellar population synthesis models. Our FUV spectra demonstrate
that the 900-1200 Å FUV can provide a strong test-bed for future WR
atmosphere and evolution models.
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关键词
Chemical abundances,Wolf-Rayet stars,Ultraviolet spectroscopy,H II regions,Spiral galaxies
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