The large-scale distribution of neutral hydrogen in the Fornax region

Meryl Waugh, M. J. Drinkwater, R. L. Webster, L. Staveley-Smith, V. A. Kilborn, D. G. Barnes, R. Bhathal, W. J.G. De Blok, P. J. Boyce, M. J. Disney, R. D. Ekers, K. C. Freeman, B. K. Gibson, P. A. Henning, H. Jerjen, P. M. Knezek, B. Koribalski, M. Marquarding, R. F. Minchin, R. M. PriceM. E. Putman, S. D. Ryder, E. M. Sadler, F. Stootman, M. A. Zwaan

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Using data from the HI Parkes All Sky Survey (HIPASS), we have searched for neutral hydrogen in galaxies in a region ∼25 × 25 deg2 centred on NGC 1399, the nominal centre of the Fornax cluster. Within a velocity search range of 300-3700 km s-1 and to a 3σ lower flux limit of ∼40 mJy, 110 galaxies with Hi emission were detected, one of which is previously uncatalogued. None of the detections has early-type morphology. Previously unknown velocities for 14 galaxies have been determined, with a further four velocity measurements being significantly dissimilar to published values. Identification of an optical counterpart is relatively unambiguous for more than ∼90 per cent of our HI galaxies. The galaxies appear to be embedded in a sheet at the cluster velocity which extends for more than 30° across the search area. At the nominal cluster distance of ∼20 Mpc, this corresponds to an elongated structure more than 10 Mpc in extent. A velocity gradient across the structure is detected, with radial velocities increasing by ∼500 km s-1 from south-east to north-west. The clustering of galaxies evident in optical surveys is only weakly suggested in the spatial distribution of our HI detections. Of 62 HI detections within a 10° projected radius of the cluster centre, only two are within the core region (projected radius <1°) and less than 30 per cent are within 3.5°, suggesting a considerable deficit of HI-rich galaxies in the centre of the cluster. However, relative to the field, there is a 3(±1)-fold excess of HI-rich galaxies in the outer parts of the cluster where galaxies may be infalling towards the cluster for the first time.

Original languageEnglish
Pages (from-to)641-656
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number2
Publication statusPublished - 1 Dec 2002
Externally publishedYes


  • Galaxies: clusters: individual: Fornax
  • Galaxies: evolution
  • Large-scale structure of Universe
  • Radio lines: galaxies
  • Surveys

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