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Multiple Merging Events in the Double Cluster A3128/A3125
Multifiber spectroscopy has been obtained for 335 galaxies in the fieldof the double cluster A3128/A3125, using the 2dF multifiber positioneron the Anglo-Australian Telescope. When combined with previouslypublished results, a total of 532 objects in the double cluster now haveknown redshifts. We have also obtained a 20 ks Chandra ACIS-I image ofthe central 16'×16' of A3128 and radioimaging of the cluster with the Molonglo Observatory Synthesis Telescopeand the Australia Telescope Compact Array. The spatial/kinematicdistribution of redshifts in the field of A3128/A3125, when combinedwith the Chandra ACIS-I image of A3128, reveals a variety ofsubstructures present in the galaxy distribution and in the hotintracluster medium (ICM). The most striking large-scale feature in thegalaxy distribution is a relatively underpopulated redshift zone ~4000km s-1 on either side of the mean cluster velocity at ~17,500km s-1. We attribute this depletion zone to the effect of theextensive Horologium-Reticulum (H-R) supercluster, within whichA3128/A3125 is embedded. In addition to this large-scale feature,numerous smaller groups of galaxies can be identified, particularlywithin the underpopulated region within +/-4000 km s-1 of themean cluster redshift. Because of the large gravitational influence ofthe H-R supercluster, these groups arrive at A3128 with a high infallvelocity, well in excess of the local sound speed. Two of these groupsappear as elongated filaments in position-velocity diagrams, indicatingthat they are tidally distended groups that have been disrupted after aclose passage through A3128. In fact, A3125 itself appears to be in sucha postpassage condition. We have identified a primarynortheast-southwest merger axis connecting A3128 with A3125, along whichthe filaments are also oriented. In addition, the Chandra image revealsthat the X-ray emission is split into two components, each with verysmall core radii, that are separated by ~1 Mpc along thenortheast-southwest axis. We have combined the redshift, X-ray, andradio data to propose that the complex X-ray morphology revealed in theChandra image is likely the result of a hypersonic infall of arelatively small group into A3128. The group produces a major disruptionin the ICM as a result of its high infall velocity.
| An Einstein X-Ray Survey of Optically Selected Galaxies. I. Data
We present the results of a complete Einstein imaging proportionalcounter X-ray survey of optically selected galaxies from theShapley-Ames Catalog, the Uppsala General Catalogue, and the EuropeanSouthern Observatory Catalog. Well-defined optical criteria are used toselect the galaxies, and X-ray fluxes are measured at the opticallydefined positions. The result is a comprehensive list of X-ray detectionand upper limit measurements for 1018 galaxies. Of these, 827 haveeither independent distance estimates or radial velocities. Associatedoptical, redshift, and distance data have been assembled for thesegalaxies, and their distances come from a combination of directlypredicted distances and those predicted from the Faber-Burstein GreatAttractor/Virgocentric infall model. The accuracy of the X-ray fluxeshas been checked in three different ways; all are consistent with thederived X-ray fluxes being of <=0.1 dex accuracy. In particular,there is agreement with previously published X-ray fluxes for galaxiesin common with a 1991 study by Roberts et al. and a 1992 study byFabbiano et al. The data presented here will be used in further studiesto characterize the X-ray output of galaxies of various morphologicaltypes and thus to enable the determination of the major sourcescontributing to the X-ray emission from galaxies.
| New nebulae and nebulous stars.
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