The reddening of radio elliptical galaxies

The photometric properties of radio-emitting and radio-quiet elliptical galaxies are compared. A statistically significant reddening of the radio ellipticals is evident for galaxies of a given optical luminosity, of ∼ 0.04, 0.03, 0.03 mag in |$(u-V)^\text{KEM}_{0.5},(b-V)^\text{KEM}_{0.5} \enspace\text {and}\enspace(V-r)^\text{KEM}_{0.5}$| respectively. There is also evidence that radio ellipticals display less scatter in their colours. The reddening is interpreted as being due to extinction by dust within the radio ellipticals, requiring ∼ 108M⊙ of gas. This supports the idea that a high gas content and nuclear activity are related, and may be accommodated within the framework of galactic wind models.