Ashok K. Singal, Kamlesh Rajpurohit
We investigate the dependence of the Fanaroff-Riley (FR) I/II dichotomy of radio galaxies on their luminosities and redshifts. Because of a very strong redshift-luminosity correlation (Malmquist bias) in a flux-limited sample, any redshift-dependent effect could appear as a luminosity related effect and vice versa. A question could then arise - do all the morphological differences seen in the two classes (FR I and II types) of sources, usually attributed to the differences in their luminosities, could these all as well be a result of mainly a cosmological evolutionary effect (e.g., due to the changing ambient density) with cosmic epoch? Even a sharp break in luminosity, seen among the two classes, could after all reflect a rather critical ambient density value. A doubt on these lines does not seem to have been raised in past and things have never been examined keeping this particular aspect in mind. We want to ascertain the customary prevalent view in the literature that the systematic differences in the two broad morphology types of FR I and II radio galaxies are indeed due to the differences in their luminosities, and not a manifestation of an evolutionary effect of the cosmic epoch. Here we investigate the dependence of FR I and II dichotomy of radio galaxies on luminosity and redshift by using the 3CR sample, where the FR I and II dichotomy was first seen, supplemented by data from two additional samples (MRC and B3-VLA), which go about a factor of 5 or more deeper in flux-density than the original 3CR sample. This lets us compare sources with similar luminosities but at different redshifts as well as examine sources at similar redshifts but with different luminosities, thereby allowing us a successful separation of the otherwise two intricately entangled effects.
View original:
http://arxiv.org/abs/1212.0667
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