The redshift dependence of spectral index in powerful radio galaxies |
| |
| Authors: | Ramana M Athreya Vijay K Kapahi |
| |
| Institution: | (1) National Centre for Radio Astrophysics (TIFR), Pune University Campus, P.O. Bag 3, 411 007 Pune, India;(2) Present address: l’lnstitut d’ Astrophysique de Paris, 98 bis Bd, 75014 Arago, Paris |
| |
| Abstract: | We present and discuss in this paper the rest frame radio spectra (1–25 GHz) of a sample of fourteen radio galaxies atz >2 from the newly defined MRC/1Jy complete sample of 558 radio sources. These galaxies are among the most powerful radio sources
known and range in luminosity from 1028-1028·8 watt Hz-1 at 1 GHz. We find that the median rest frame spectral index of this
sample of galaxies atz >2 is significantly steeper than that of a matched luminosity sample of 3CRR galaxies which are at a much lower redshift (0.85
<z < 1.7). This indicates that spectral index correlates primarily with redshift, at least in the luminosity range considered
here. The difference between the distributions of rest frame spectral curvatures for the two samples does not appear to be
statistically significant.
We suggest a new explanation for the steeper spectra of radio galaxies at high redshift involving steeper electron energy
spectra at injection. Electron energy spectra are expected to steepen in a first-order Fermi acceleration process, at both
non-relativistic and relativistic shock fronts, as the upstream fluid velocity decreases. This may well be the case at high
redshifts: the hotter and denser circum-galactic medium at high redshifts could result in slower speeds for the hotspot and
the jet material behind it. The smaller sizes of radio sources at higher redshifts provide support to this scenario.
Since deceased. |
| |
| Keywords: | Galaxies: radio spectra high redshift radio synchrotron electron acceleration |
| 本文献已被 SpringerLink 等数据库收录！ |
|
