Integral Properties of Spiral and Irregular Galaxies

Abstract

view Abstract Citations (306) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Integral Properties of Spiral and Irregular Galaxies Roberts, Morton S. Abstract General properties of, and relations among, a sample of 98 spiral- and irregular-type galaxies are derived and discussed. The sample represents those galaxies for which total mass (91 systems) and/or H I mass (77 systems) are available. Data derived from optical and 21-cm observations are used. Where necessary, optically derived masses have been adjusted to yield a total mass estimate using a model fractional-mass distribution curve. Masses derived from optical and 21-cm measurements are compared and found to be in good agreement, although the latter appear higher in the mean, by a factor of about 2. Because of the different assumptions made in deriving total masses from optical and from 21-cm measurements, it is not known which, if either, approach yields the true total mass. Hydrogen masses, usually derived on the basis of small optical depth in the hydrogen line, are found to be dependent on the inclination of the system, implying an optical depth effect. A statistical correction is derived and applied to the present set of data. The ratios and relations formed from the integral parameters of total mass, hydrogen mass, and absolute photographic luminosity . The average ratios of hydrogen mass to luminosity and hydrogen mass to total mass vary systematically with galaxy type (Table V and Figs. 7 and 10). Such variation has been from a much smaller sample size. Contrary to previous views, the ratio of total mass to luminosity does not appear to vary significantly with structural type over the range Sa-Ir (Table V and Fig. 12). The over-all average is 7.5. The hydrogen mass-luminosity, hydrogen mass-total mass, and total massluminosity relations for spirals and irregular systems are given. Surface densities of luminosity, hydrogen, and total mass are tabulated, and the variation of the median values of these densities with structural type is shown. Publication: The Astronomical Journal Pub Date: September 1969 DOI: 10.1086/110874 Bibcode: 1969AJ.....74..859R full text sources ADS | data products SIMBAD (99) NED (84)