Abstract
view Abstract Citations (238) References (64) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Composition Gradient across M81 Garnett, D. R. ; Shields, G. A. Abstract Spectrophotometric observations are presented for 18 H II regions in the galaxy M81 (type SAab). M81 is the earliest type galaxy for which extensive H II region observations have been made. The observed emission-line intensities have been analyzed by the empirical calibration method and by the use of photoionization models. Strong radial gradients are seen in (forbidden O II + forbidden O III)/H-beta and in the derived oxygen abundance. M81 has an abundance gradient and an overall metallicity similar to those of late-type galaxies of similar mass, luminosity, and gas fraction. This suggests that the chemical properties of galaxies are governed more by these physical characteristics than by the morphological type. There appears to be little systematic variation of N/O with radius in M81. The outlying H II region Muench 1, located 15 kpc from the nucleus, has about solar N/O but O/H about 0.2 times the solar value; in contrast, much lower N/O values occur in comparably oxygen-poor H II regions in other galaxies. The oxygen abundance and gas fraction as a function of radius in M81 are roughly consistent with a 'simple' model of chemical evolution (Searle and Sargent, 1972) with the same heavy-element yield as found for dwarf irregular galaxies. However, the low oxygen abundance in Muench 1 agrees only if the dynamically inferred 'dark mass' is excluded in computing the gas fraction. Publication: The Astrophysical Journal Pub Date: June 1987 DOI: 10.1086/165257 Bibcode: 1987ApJ...317...82G Keywords: Abundance; Astronomical Spectroscopy; Chemical Composition; Nebulae; Spiral Galaxies; H Ii Regions; Oxygen Spectra; Photoionization; Spectrophotometry; Astrophysics; GALAXIES: INDIVIDUAL MESSIER NUMBER: M81; NEBULAE: H II REGIONS; STARS: ABUNDANCES full text sources ADS | data products SIMBAD (30) NED (20)
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