The Anomalously Large Peculiar Velocity of Abell 2634
Session 30 -- Clusters of Galaxies
Display presentation, Tuesday, 9:30-6:30, Pauley Room

## [30.11] The Anomalously Large Peculiar Velocity of Abell 2634

M. Gregg (IGPP/LLNL)

\def\etal{et al.} \def\kms{\rm km/s^{-1}} \def\dnsig{\rm D_{n}-\sigma}

Based on distance estimates to 18 early type cluster members, Lucey \etal\ (1991, MNRAS 248, 804) report a peculiar velocity for Abell 2634 of $\sim -3400~\kms$. Lucey \etal\ suggest that this uncomfortably large value is spurious because IR Tully-Fisher distances to spirals in the region indicate that the late type galaxies have zero peculiar velocity (Aaronson \etal\ 1986, ApJ 302, 536). One possible explanation is that the $\dnsig$\ distance estimator for the early type galaxies has a different zero point and/or slope in Abell~2634. This could arise because of structural or stellar population differences with respect to the elliptical galaxies in Virgo and Coma which are used to calibrate the $\dnsig$\ relation.

To confirm the Lucey \etal\ result and look for an explanation, new images and spectroscopy were obtained in September 1992 at Kitt Peak National Observatory of 20 early type galaxies in Abell~2634, including 6 additional cluster members outside the central region studied by Lucey \etal\ ~~Preliminary results for 14 objects yield a value of $-3100~\kms$\ for the cluster peculiar velocity, in excellent agreement with the Lucey study. There is close correspondence between the individual galaxy peculiar velocities from the Lucey \etal\ study and the Kitt Peak data, demonstrating that large errors are not the cause of the spurious peculiar velocity and strongly suggesting that an additional parameter is at work modifying the $\dnsig$\ relation in this cluster.

The early type galaxies have normal BVR colors and none of the spectra have emission lines. There is a significant correlation between the 4000 \AA\ break strength and peculiar velocity in that galaxies with smaller breaks have larger negative peculiar velocities. This is difficult to understand, but is consistent with the weak correlation between surface brightness and peculiar velocity reported by Lucey \etal\ ~~Work is continuing to search for spectroscopic and structural clues which may explain the anomalous peculiar velocity of Abell~2634.