H II regions as extragalactic distance indicators. II - Application of isophotal diameters. III - Application of H II region fluxes and galaxy diameters

Details H II regions as extragalactic distance indicators. II - Application of isophotal diameters. III - Application of H II region fluxes and galaxy diameters H II regions as extragalactic distance indicators. II - Application of isophotal diameters. III - Application of H II region fluxes and galaxy diameters

Mar 1979

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979apj...228..696k&link_type=abstract

Astrophysical Journal, Part 1, vol. 228, Mar. 15, 1979, p. 696-711.

Astronomy and Astrophysics

Astrophysics

34

Astrometry, Galactic Radiation, H Ii Regions, Luminous Intensity, Nebulae, Calibrating, Diameters, Distance, H Alpha Line, Hydrogen Ions, Isophotes, Red Shift, Size Determination

Scientific paper

Isophotal diameters of the largest H II regions in late-type galaxies are calibrated and applied to the galaxies measured by Sandage and Tammann (ST: 1974, 1975) in their calibration of the extragalactic distance scale. The results are found to corroborate ST's general conclusions regarding the usefulness of H II region diameters as distance indicators, but also to suggest the presence of systematic errors in the diameters determined by ST for distant H II regions. An increase of about 40% (from 50 to approximately 75 km/s per Mpc) in the derived Hubble constant is obtained by adopting more physically based isophotal diameters. The derived distance scales are then compared with cruder scales determined from the H-alpha fluxes of the largest H II regions and from the diameters of the galaxies themselves, as defined by the H II regions. The presence of systematic errors in ST's results is confirmed, and evidence is found suggesting a small change in the distance scale in the direction of increasing Hubble constant.

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