Radio galaxies in the 2SLAQ Luminous Red Galaxy survey: II. The stellar populations of radio-loud and radio-quiet LRGs
Helen M. Johnston, Elaine M. Sadler, Russell Cannon, Scott M. Croom,, Nicholas P. Ross, Donald P. Schneider

TL;DR
This study analyzes the stellar populations of radio-loud and radio-quiet luminous red galaxies at redshift 0.4-0.7, finding that powerful radio sources are associated with younger stars and stronger emission lines, while less powerful sources show no significant differences.
Contribution
It provides new insights into the relationship between radio power and stellar populations in luminous red galaxies at intermediate redshifts.
Findings
No evolution in young stellar populations with redshift.
Powerful radio sources have younger stars and stronger emission lines.
A threshold in radio power (~10^26 W/Hz) where emission lines activate.
Abstract
We present an analysis of the optical spectra of a volume-limited sample of 375 radio galaxies at redshift 0.4<z<0.7 from the 2dF-SDSS Luminous Red Galaxy and QSO (2SLAQ) redshift survey. We investigate the evolution of the stellar populations and emission-line properties of these galaxies. By constructing composite spectra and comparing with a matched sample of radio-quiet sources from the same survey, we also investigate the effect on the galaxy of the presence of an active nucleus. The composite spectra, binned by redshift and radio luminosity, all require two components to describe them, which we interpret as an old and a younger population. We found no evolution with redshift of the age of the younger population in radio galaxies, nor were they different from the radio-quiet comparison sample. Similarly, there is no correlation with radio power, with the exception that the most…
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