A luminosity classification of northern Sb galaxies
Date
1977
Authors
Stenning, Mark Cheveley
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Abstract
The DDO system of luminosity classification has been applied to 670 Sb galaxies listed in the Uppsala General Catalogue. UGC diameter and magnitude information, which was found to correlate well with similar information in the Second Reference Catalogue of Bright Galaxies, was corrected for absorption effects in accordance with methods outlined in the RCBG2. These modified data were then used to examine the luminosity function and velocity-magnitude-diameter relationships. Absolute magnitude calibration was accomplished using recent estimates of the distance moduli of M31 and M81.
Magnitude-diameter relationships were found to agree well with both theoretical and other observational results; in particular, the absolute luminosity-diameter relation L = D².⁶⁷±.¹⁴ was obtained. The luminosity function for Sb galaxies , based on a total spatial density of 3.5 x 10⁻³ Mpc⁻³, increases exponentially from the supergiant to the normal giant class beyond which it abruptly terminates, although some evidence for a fainter (III+) class is discussed.
The Malmquist effect was prominent on the initial Hubble diagrams and when it was accounted for following the precepts of Sandage and Tammann, a value of H =70km sec⁻¹ Mpc⁻¹ was obtained. The Malmquist effect was then rediscussed in terms of an implication of the luminosity function and a Malmquist correction based on individual class absolute magnitude-diameter relationships was made. The revised Hubble diagrams showed little dispersion and had slopes consistent with the theoretical value over the velocity range of the data (Vₒ≤ 10⁴km s⁻¹). From the revised Sb I-II diagram a Hubble constant of 95(+18,-14) was obtained. Supportive evidence was found f or the Rubin-Ford effect although the present study lacks the southern galaxies necessary to make a rigourous investigation of this phenomenon. Finally, luminosity classifications were used to help ascertain group and pair memberships.