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

Abstract

Using data from the H I Parkes All Sky Survey (HIPASS), we have searched for neutral hydrogen in galaxies in a region ∼25 × 25 deg 2 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 H I 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 H I 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 H I detections. Of 62 H I 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 H I-rich galaxies in the centre of the cluster. However, relative to the field, there is a 3(±1)-fold excess of H I-rich galaxies in the outer parts of the cluster where galaxies may be infalling towards the cluster for the first time.The Fornax cluster is amongst the closest and most well-studied clusters in the southern sky, providing an interesting nearby field for the study of large-scale structure (LSS), galaxy populations, dynamics and evolution in the cluster environment. Although the C 2002 RAS

A multibeam H i survey of the Virgo cluster - two isolated H i clouds?

“…sample (Zwaan et al 2003), identification of high-velocity clouds (Putman et al 2002), the measurement of tidal streams (Boyce et al 2001), the identification of optically faint gas rich objects (Minchin et al 2003) and a measurement of the total H I content of clusters (Barnes et al 1997;Waugh et al 2002). It is a continuation of this latter work that we discuss in this paper.…”

The HIPASS catalogue: ΩH i and environmental effects on the H i mass function of galaxies

“…It should also be kept in mind that the dynamic range in densities probed by HIPASS is smaller than that probed by optical surveys. For example, Waugh et al (2002) showed that cluster centres that are readily apparent in the counts of optical galaxies are only detected as over-densities of a few times the density of H I-detected galaxies in the field. At first sight, our findings seem to be in conflict with the recent results of Springob et al (2004), who, based on optically selected galaxies, claimed a flattening of the HIMF toward higher density regions.…”

Tidal origin of NGC 1427A in the Fornax cluster

“…Bureau et al 1996, Drinkwater et al 2001a, Waugh et al 2002. Many of these surveys are broadly focused on general detection and cluster properties as a whole.…”

“…The nearest HIPASS detected Hi-rich galaxies to NGC 1427A are ESO358-051 (HIPASS J0341-34; 03h 41m 06s, -35°56 02 , F H I = 4.84 Jy km s −1 , v H I = 1734 km s −1 ), ESO358-060 (HIPASS J0345-35; 03h 45m 12s, -35°34 07 , F H I = 11.34 Jy km s −1 , v H I = 803 km s −1 , and NGC 1437A (HIPASS J0342-36; 03h 42m 52s, -35°17 26 , F H I = 7.61 Jy km s −1 , v H I = 895 km s −1 ; Waugh et al 2002). The ATCA data for these galaxies detect comparable amounts of Hi to the values measured from HIPASS.…”