Bent Double Radio Sources from the FIRST Survey
- Michael Gregg, Adam Stanford, Bob Becker (U.C. Davis)
- Elizabeth Blanton, David Helfand (Columbia U.)
As a double-lobed radio source passes through a cluster of galaxies,
the drag of the intracluster medium on the radio plasma gives the
lobes a swept-back or "bent" appearance. Thus, bent doubles can
signal the presence of a cluster. Many nearby clusters have bent
double radio sources; the Coma cluster has 2 and Abell 119 has
Here are some example bent double radio sources from the FIRST
Click on the image to see all 384 radio sources in our present
In imaging and spectroscopic followup of about 100 bent double
fields, we have found clusters to z = 0.84.
The source numbered 256 above is in this rich cluster, at z=0.64.
From Keck spectroscopy of 10 galaxies in this field, we derive a
velocity dispersion of 1000 km/s, comparable to the Coma cluster.
Our collaboration is beginning a systematic imaging survey of 80 bent
doubles which have NO optical counterparts on the Digitized
Sky Survey. The hope is that these radio sources mark the locations
of distant clusters (z > 1).
Although bent doubles do not occur in all clusters, they are an
unbiased tracer of large scale structure and are relatively immune to
the selection effects of optical and X-ray searches. The FIRST Survey
will ultimately cover 10,000 sq. degrees centered on the north
Galactic cap; by searching for clusters and density enhancements using
bent doubles, it will be possible to map structures on extremely large
scales and over great distances.