AAS 207th Meeting, 8-12 January 2006
Session 179 Evolution of Galaxies, and Galaxies Surveys at Low Redshift
Poster, Thursday, 9:20am-4:00pm, January 12, 2006, Exhibit Hall

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[179.23] Complex Structure in the ALFALFA HI Distribution around VirgoHI21

M.P. Haynes (Cornell and NAIC), R. Giovanelli, B.R. Kent, A. Saintonge, S. Stierwalt (Cornell), B. Catinella, E.M. Momjian (NAIC), G.L. Hoffman (Lafayette Coll.), J.R. Rosenberg (Harvard-CfA), N. Brosch (Wise Obs.), J.I. Davies (Cardiff), R.L. Minchin (NAIC)

One of the principal drivers of the ALFALFA survey is the exploration of the dynamics of the Virgo cluster and its environs via the cataloguing of all of its gas-rich members and tracing disruptive events through the HI remnants they leave behind. The wide area coverage provided by ALFALFA is ideal for the study of extended source structures, and its sensitivity, bandwidth and resolution allow the detection of HI over the full Virgo redshift range as well as the identification of gas-rich background objects. The Spring 2005 ALFALFA survey dataset contains nearly-complete two-pass coverage of a wide field around the enigmatic "dark" HI cloud VirgoHI21, suggested by Minchin et al. to be responsible for the distortions evident in the peculiar, one-armed spiral NGC 4254. We find clear evidence of a continuous connection between VirgoHI21 and NGC 4254. The extended HI distribution can be traced over 30 arcmin to the north of NGC 4254 and is clumpy in places. We apply the ALFALFA signal extractor to construct a catalog of HI detections in this region, present integrated maps of the complex extended structures, and discuss the nature of VirgoHI21 in the context of this very rich Virgo environment. This work has been supported by NSF grants AST-0307661 and AST-0435697 and by the Brinson Foundation.

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