The dynamics of the outer regions of the Coma cluster

We apply the spherical infall model to compare the observed distribution of radial velocities of galaxies around Coma with predictions that are based on optical and X-ray overdensity profiles. Two optically selected galaxy catalogues, the CfA redshift survey and a UKST plate scanned with the APM, are used to determine the over-density profile of the cluster. The two sets of predicted caustics in the angular separation-redshift diagram are compared with a radial velocity catalogue which we have extended significantly in the range between 1° and 4° from the centre of the Coma cluster. In total, we have measured 98 new redshifts. Despite almost doubling the number of radial velocities in this interval, we fail to find the caustics with any degree of certainty