An analysis of the cosmological evolution of radio sources. II - Evolution functions for flat- and steep-spectrum sources at 1400 MHz

Details An analysis of the cosmological evolution of radio sources. II - Evolution functions for flat- and steep-spectrum sources at 1400 MHz An analysis of the cosmological evolution of radio sources. II - Evolution functions for flat- and steep-spectrum sources at 1400 MHz

Jan 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981a%26as...43...91m&link_type=abstract

Astronomy and Astrophysics Supplement Series, vol. 43, Jan. 1981, p. 91-98.

Astronomy and Astrophysics

Astronomy

5

Astronomical Models, Cosmology, Evolution (Development), Extragalactic Radio Sources, Radio Astronomy, Graphs (Charts), Radiant Flux Density, Red Shift

Scientific paper

The problem of predicting 1400 MHz number-counts of sources within a specified spectral index range as well as expected variations in spectral index distributions with 1400 MHz flux density is investigated in terms of cosmological evolution of extragalactic radio sources. It is shown that recently proposed models of evolution, which were not tested by spectral-index dependent counts (e.g. Katgert, 1977 Kulkarni, 1978), cannot predict the observed counts of flat- and very steep-spectrum sources at 1400 MHz. Assuming the existence of two classes of sources, namely flat- and steep-spectrum ones, it is concluded that their space densities are characterized by different evolution functions. These evolution functions, especially the function for the main class of (steep-spectrum) sources, should be dependent not only on luminosity and redshift but also on spectral index. Such an evolutionary model predicts source counts and spectral index distributions which are perfectly consistent with observations. Also, the predicted redshift distributions are not discrepant with the observed, however, incomplete redshifts. Consequences of a dependence of the cosmological evolution on spectral index is discussed.

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