The changing interstellar medium of massive elliptical galaxies and cosmic evolution of radio galaxies and quasars |
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| Authors: | A Mangalam Gopal-Krishna Paul J Wiita |
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| Institution: | Indian Institute of Astrophysics, Sarjapur Road, Koramangala, Bangalore 560034, India;National Centre for Radio Astrophysics/TIFR, Post Bag 3, Pune University Campus, Pune 411007, India;School of Natural Sciences, Institute for Advanced Study, 1 Einstein Drive, Princeton, NJ 08540, USA;Department of Physics &Astronomy, Georgia State University, PO Box 4106, Atlanta, GA 30302-4106, USA |
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| Abstract: | The recently discovered apparent dramatic expansion in the effective radii of massive elliptical galaxies from z ? 2 to ?0.1 has been interpreted in terms of either galaxy mergers or the rapid loss of cold gas due to active galactic nuclei (AGN) feedback. In examining the latter case, we have quantified the extent of the expansion, which is uncertain observationally, in terms of the star formation parameters and time of the expulsion of the cold gas. In either case, the large global decrease in stellar density should translate into a major drop in the interstellar medium density and pressure with cosmic epoch. These cosmological changes are expected to have a major influence on the gas accretion mode, which will shift from 'cold' thin disc accretion at high redshifts towards 'hot' Bondi fed Advection Dominated Accretion Flow (ADAF) accretion at low redshifts. The decline of angular momentum inflow would then lead to a spin down of the black hole, for which we have calculated more precise time-scales; a value of about 0.2 Gyr is typical for a 109 M⊙ central black hole. These results have implications for the different cosmological evolutionary patterns found for the luminosity functions of powerful and weak radio galaxies. |
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| Keywords: | black hole physics galaxies: active galaxies: evolution galaxies: jets galaxies: ISM galaxies: interactions |
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