Radio Galaxy Zoo: Optical and infrared colors of radio host galaxies


Working notes on the optical/infrared properties of the consensus host galaxies from Radio Galaxy Zoo.

LR’s recent emails and main points

SDSS \((u-r)\) colors of the RGZ hosts are consistent with expectations for giant elliptical galaxies. The majority of the \(\sim3200\) galaxies lie along the red sequence, with a small amount of scatter at higher redshifts. Earlier results showing them all over the map were likely due to a combination of galaxies near the telescope observable limit and/or \(u\)-band dropouts.

The small fraction of RGZ hosts in the blue cloud are interesting and potentially worthy of individual follow-up; they might either be genuine spirals or blue ellipticals with recent amounts of star formation, possibly merger induced.

Optical color-magnitude diagram of SDSS counterparts to Radio Galaxy Zoo hosts, split as a function of redshift. Dashed line shows the fit to the red sequence at \(z=0.10\); neither the slope nor offset of the red sequence for RGZ hosts evolves significantly out to at least \(z=0.40\).