Global Jet Watch

Abstract:

THE most distant astronomical objects observed are quasars at redshifts of z ≃ 4.9 (ref. 1), corresponding to a time when the Universe was less than a billion years old. This leaves little time during which the quasars and their host galaxies could form. In principle, the evolutionary state of the host galaxies can be probed by determining how many stars have formed, but this task is not straightforward because light from the quasar itself overwhelms any accompanying starlight. High-redshift radio galaxies-the likely progenitors of luminous elliptical galaxies-provide better targets for such studies, as optical emissions from their active nuclei are observed to be faint. Here we report the discovery of a radio galaxy (6C0140 + 326) at z = 4.41 which shows no evidence for either a stellar continuum or an unobscured quasar nucleus. We conclude that the galaxy associated with the radio source is neither fully formed nor obviously in the process of forming stars. This implies that at least some giant elliptical galaxies are still immature at z ≃ 4.5, and that if the intense bursts of star formation thought to produce the bulk of their stellar populations occur during the radio-bright phase, these star-forming regions are obscured by dust and gas.

Abstract:

A multi-radio-frequency study of the unusual structure of the radio galaxy 3C 171 is presented. A spectral index study is used to make deductions about the origins of the plumes which emanate from the hotspots. Optical images are overlaid on radio maps which give support to the inference that the plumes are diverted backflow from the hotspots. Evidence is presented which supports the interpretation of the region of enhanced brightness in the north-west plume as a quasi-hotspot, and thus that there is a widely separated primary and secondary hotspot pair in 3C 171.

Abstract:

A model is presented which reconciles the conflicting implications of the Garrington-Laing effect and the Liu-Pooley effect, which had caused difficulties for the projection model and hence for unified schemes. I also show that DPM asymmetries are significantly larger for quasars than for radio galaxies, adding further weight to the suggestion that quasars are closer to the line of sight. Copyright ©1996 Elsevier Science Ltd.