Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1975
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1975apj...202..583l&link_type=abstract
Astrophysical Journal, vol. 202, Dec. 15, 1975, pt. 1, p. 583-590. Research supported by Tufts University.
Astronomy and Astrophysics
Astronomy
8
Cosmology, Hubble Diagram, Quasars, Radio Sources (Astronomy), Red Shift, Galactic Evolution, Galactic Radiation, Light Emission, Radio Galaxies, Stellar Luminosity
Scientific paper
The composite Hubble diagram for 663 normal galaxies, 235 radio galaxies, and 265 quasi-stellar objects is given. The least-squares solution to the Hubble-diagram slope for each of the three classes of objects is compatible, within errors, with that expected for a homogeneous isotropic expanding universe. If the Hubble constant is 50 km/s per Mpc, then the mean absolute visual magnitude is -21.150. The mean absolute optical luminosity is 10 to the 43.96 power ergs/s, and the dispersion in magnitude is 0.887 for normal galaxies; these parameters are -23.061, 10 to the 44.72 power ergs/sec, and 0.684 for radio galaxies; and -25.784, 10 to the 45.81 ergs/sec, and 1.451 for quasi-stellar objects. It is shown that the uncertainty in the slope of the Hubble diagram for QSOs is comparable to that obtained for normal galaxies over a similar range in magnitude. This means that the scatter in the QSO Hubble diagram should not be used in arguments which question their cosmological nature. It is shown that the absolute optical luminosity of extragalactic objects increases with increasing redshift and that any given object class occurs infrequently in the magnitude and redshift range of the others. These facts suggest an evolutionary sequence in which bright young QSOs evolve into older, less luminous radio galaxies, which in turn evolve into the weaker, still older normal galaxies.
Johanson J. M.
Lang Kenneth R.
Lord Steve D.
Savage P. D.
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