Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999aj....117..157s&link_type=abstract
The Astronomical Journal, Volume 117, Issue 1, pp. 157-166.
Astronomy and Astrophysics
Astronomy
11
Galaxies: Spiral, Luminosity Function, Mass Function
Scientific paper
A distance-limited subset of the complete flux-limited sample of Sc galaxies in the Revised Shapley-Ames Catalog of Bright Galaxies is isolated by means of separate Spaenhauer diagrams for six individual van den Bergh luminosity class intervals from Sc I+I.2,.3 to Sc III-IV. The distribution functions of kinematic absolute B^0,i_T(220,50) magnitudes and 21 cm line widths, W_20, corrected to edge-on orientation, have been determined for the same six bins of luminosity class. The individual luminosity functions for each luminosity class are bounded on both the bright and faint ends, showing that the present sample includes no dwarf Sc spirals fainter than M(B_T)(220,50)=-18 belonging to luminosity classes I to III-IV, as defined by the regularity of the spiral pattern. Star-forming galaxies with spiral structures as regular as the ones found in these luminosity classes have absolute magnitudes brighter than M_B(H=50)=-18 and 21 cm line widths larger than W_20/sini=2v_rot(max)=165 km s^-1. Furthermore, the 21 cm line-width distributions move toward smaller rotational velocities as the luminosity classes change from I to III, showing that rotation is a principal parameter determining the regularity of the spiral pattern. Whether it is the only parameter awaits a similar investigation for spirals of all luminosity classes along the complete Hubble sequence. In particular, it has not yet been proved that all Im and Sm galaxies, where, by definition, the spiral arms are either lacking or are semichaotic, have absolute magnitudes that are fainter than M_B=-18 and whose 21 cm LWs are smaller than ~165 km s^-1, presumably because of smaller mass than the high-luminosity, regular spirals. The Teerikorpi ``cluster population incompleteness bias'' is demonstrated again. Here, however, as in Papers II-IV of this series, we use field galaxies to show that the slope and zero point of the Tully-Fisher (T-F) relation are systematically incorrect for flux-limited samples, the error increasing with redshift. The data also support the possibility that the zero point of the T-F relation for Sc galaxies, even in the distance-limited sample, is a function of luminosity class, varying by 0.42 mag between Sc I+I.2,.3 and Sc III galaxies if the slope of the T-F relation for each class is taken to be that of the fundamental calibrating galaxies with Cepheid distances. If true, this is presumably due to differences in the mass distribution and, therefore, in the resulting rotational velocity field as a function of luminosity class even within a fixed Hubble type.
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