Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1979
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979apj...234..775t&link_type=abstract
Astrophysical Journal, Part 1, vol. 234, Dec. 15, 1979, p. 775-784. Research supported by the Swiss National Science Foundation
Astronomy and Astrophysics
Astronomy
104
Galactic Clusters, Galactic Radiation, Local Group (Astronomy), Luminous Intensity, Radial Velocity, Spiral Galaxies, Distance, Elliptical Galaxies, Hubble Diagram, Red Shift, Velocity Distribution, Virgo Galactic Cluster
Scientific paper
Galaxies of all morphological classes in the Revised Shapley-Ames (RSA) catalog show the same type of correlation between absolute magnitude and redshift as was found for E and SO galaxies in Paper I of this series. Mean absolute magnitudes become brighter with increasing redshift due to the bias caused by a broad luminosity function for objects in a magnitude limited sample. Using the methods developed in Paper I, we have computed luminosity and catalog completeness functions for five separate luminosity classes (Lc) of Sc galaxies, two of Sb, and one of Sa. These functions have been obtained with and without applying corrections for internal absorption caused by different inclinations and, together with the E and SO functions determined in Paper I, cover all classes of the RSA.
The bright ends of φ(M) for Sc galaxies do become progressively fainter as the luminosity classes change from I to IV, but the overlap in M between the classes is large. There is a spread of more than 3 mag in Mn within any given luminosity class. The brightest Sc III-IV galaxies (MB ≍ -21.5) are brighter than the faintest Sc I systems (MB ≍ -19.5). If this large overlap in luminosities between the van den Bergh classes is confirmed when more precise luminosity classifications become available for the RSA galaxies in the future, then the luminosity of any given galaxy would apparently not be the sole parameter that determines Lc, and the concept of luminosity class would be more complex than is now generally believed.
Calculated effective luminosity functions at given redshifts are displayed, and the predicted ratios of Sc I-Il/Sc Ill/Sc III-IV systems are given for five velocity intervals from υ0 < 1250 km s-1 to υ0 > 3500 km s-1. Not surprisingly, Sc I galaxies dominate the distribution of spirals in the RSA for υ0 > 3500 km s-1, while Sc III and IV systems are in the majority for υ0 < 1250 km s-1.
The correlations of on log υ0 for the different classes are used to calculate the photometrically expected velocity p of the Virgo cluster. The method uses only the observed distribution of apparent magnitudes of cluster members of given morphological types and of Lc classes. Comparison of p with the directly observed systemic velocity 0 gives a peculiar motion of Virgo (relative to the velocity frame of the RSA) of 60 ± 132 km s-1. Such a small peculiar motion, although not particularly well determined by this new method, nevertheless agrees with previous determinations by Sandage and Tammann, Kormendy, and others using different methods. Assuming that there is no uniformly distributed unseen mass that would significantly reduce the observed density contrast toward Virgo, this result requires that q0 < 0.1 by a wide margin.
An estimate of the global mass-to-luminosity ratio follows by summing the luminosity density for each morphological type and luminosity class. The total volume emissivity contributed by all galaxies of all types and luminosities (averaged over the volume spanned by the RSA) is L = 11 × 107 solar B luminosities per Mpc3, as found by integrating the present individual luminosity functions and summing. Correction to the lower global value by a factor of 1.5 to account for local density enhancement gives the global ratio of total mass to visible B luminosity (in solar units) of / = 1900q0. An open universe with q0 = 0.02 (Paper IV) would yield / = 40, in agreement with recent estimates in galaxies, and would imply that most of the matter in the Universe is in galaxies. By comparison, an / of ∼1000 is required to close the Universe.
Sandage Alan
Tammann Gustav A.
Yahil Amos
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