The spectral indices in the optical continuum of the QSOs, BL Lacertae objects and the nuclei of Seyfert, N and normal galaxies

Details The spectral indices in the optical continuum of the QSOs, BL Lacertae objects and the nuclei of Seyfert, N and normal galaxies The spectral indices in the optical continuum of the QSOs, BL Lacertae objects and the nuclei of Seyfert, N and normal galaxies

Apr 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981ap%26ss..75..473t&link_type=abstract

Astrophysics and Space Science, vol. 75, no. 2, Apr. 1981, p. 473-499.

Astronomy and Astrophysics

Astrophysics

8

Astronomical Spectroscopy, Bl Lacertae Objects, Galactic Nuclei, Quasars, Astronomical Catalogs, Continuous Spectra, Linear Polarization, Seyfert Galaxies, Statistical Distributions

Scientific paper

The hypothesis that the optical continua of QSOs, BL Lac objects and the nuclei of Seyfert, N and normal galaxies arise due to incoherent synchrotron radiation from electrons and consequently the flux of radiation in the optical continua of these objects is given by the power law: F(v) v~ is examined. Following Kinman, spectral indices cEB-V and aUB in (B V) and (U - B) colours as well as their average (a) and difference z~a have been defined and calculated for samples of 227 QSOs, 32 BL Lac objects and nuclei of 62 Seyfert, 12 N and 7 normal galaxies. Here (a) has been assumed to be an estimate of the spectral index a. On the other hand, ~a has been regarded as a measure of departure from the power law. On the basis of this, the distributions of z~a and (a) in QSOs, BL Lac objects and the nuclei of Seyfert, N and normal galaxies have been studied. The value of a depends mainly on the balance of the energy loss due to synchrotron radiation and the rate of replenishment of energy by injection of high energy electrons in the radiating region. The increase in the value of a and therefore that of (cx) indicates that the activity in the object is slowing down and the object is growing older. Assuming that the QSOs, BL Lac objects and the nuclei of Seyfert, N and normal galaxies essentially represent different phases in the evolutionary sequence of extragalactic objects, we suggest that they may be arranged in the sequence: QSOs -~ BL Lac objects -* Seyferts 1 -~ N galaxies -~ Seyferts 2 -* Normal galaxies in the decreasing order of activity in the core or nuclei of these objects

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