THE ASTRONOMICAL JOURNAL    VOLUME 113, NUMBER 6, PAGE 1939         JUNE 1997

             A VLA SURVEY OF THE HERCULES CLUSTER. I. THE H I DATA

                                JOHN M. DICKEY

    Department of Astronomy, University of Minnesota, 116 Church Street SE,
     Minneapolis, Minnesota 55455; Electronic mail: john@astro.spa.umn.edu

                                   ABSTRACT

     This paper presents results from a survey of lambda 21-cm emission
     from galaxies in the Hercules Cluster, A2151 and A2147. Four VLA
     primary beam areas were covered, a total area of 0.9 square degrees,
     including some 120 spiral galaxies brighter than 17.5m. The velocity
     resolution is 44 km/s, the angular resolution 25". The detection
     threshold at field center is 2.6 x 10^8 h^{-2} Msun in H I mass or
     about 1.8 x 10^20 cm^{-2} in column density. There are 61 galaxies
     detected in H I, of which about 25 had been previously detected at
     lambda 21-cm. About ten of the detections correspond to galaxies that
     are very faint in the optical, m_E >= 18 or M >= -17^m - 5 log h. Some
     of these low surface brightness galaxies have very extended H I disks,
     with r >= 15 kpc. The abundance of H I is a strong function of
     position in the cluster, with galaxies in the south and west showing
     hardly any gas, and galaxies in the north and east of A2151 frequently
     having massive, extended gas disks. The morphology of the remnants of
     gas in galaxies in the south and west suggests that the intracluster
     medium is responsible for their H I deficiency, but there are also
     several dramatic galaxy mergers in progress. (c) 1997 American
     Astronomical Society.