Old stellar populations in distant radio galaxies

Research output: Chapter in Book/Report/Conference proceedingConference contribution


I describe the current status of our attempts to determine the age of the oldest known stellar populations at high redshift, in the red mJy radio galaxies 53W091 (z = 1.55) and 53W069 (z = 1.43). During the past year the original conclusion of Dunlop et al. (1996) - that 53W091 is > 3 Gyr old has been questioned from two, basically orthogonal directions. First, reports that, the near-infrared light from 53W091 is highly polarized have cast some doubt, on whether its red colour is genuinely due to an old population of stars. Second, assuming that all the light is indeed due to stars, it has been claimed that 53W091 is in fact only 1-2 Gyr old. Here I present a preliminary analysis of new infrared polarimetric observations of 53W091 which show thai the first of these criticisms can bu rejected with very high confidence, I then explore why different modellers have derived different ages for 53W091, and present: new model fits to the spectrum of 53W069 which demonstrate that different spectral synthesis codes are certainly in good agreement that this galaxy is 3-4 Gyr old. Finally I present, it preliminary analysis of the morphologies and scale-lengths of 53W091 and 53W069 as described from new I-band WFPC2 HST images, anti compare the results with those for 3CR galaxies at comparable redshifts. I conclude that the scale-lengths and luminosities of radio galaxies at z similar or equal to 1.5 appear to scale together as would be predicted from the Kormendy relation for low-redshift, elliptical galaxies.

Original languageEnglish
Title of host publicationMOST DISTANT RADIO GALAXIES
EditorsHJA Rottgering, PN Best, MD Lehnert
Place of PublicationAMSTERDAM
Number of pages13
ISBN (Print)90-6984-238-6
Publication statusPublished - 1999
EventColloquium on the Most Distant Radio Galaxies - AMSTERDAM
Duration: 15 Oct 199717 Oct 1997


ConferenceColloquium on the Most Distant Radio Galaxies


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