Australia Telescope National Facility

Search for HI in Dwarf Spheroidal Galaxies
Claude Carignan, PASA, 16 (1), in press.

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New HIPASS data on Sculptor

As was discussed in sec. 4, single field synthesis observations (or single dish observations centered on the optical) are most likely missing some (if not most) of the gas present in such nearby systems where the gas is expected to cover a large area ( $\sim$ few degrees) on the sky. As was demonstrated with the study of the Magellanic System (Putman et al. 1998), the Parkes 21cm Multibeam System (PMS: Staveley-Smith et al. 1996) is best suited for this kind of study. Fig. 5 shows a

$4^{\rm o} \times 4^{\rm o}$ field around Sculptor obtained with the PMS. It can be seen that the detected gas is very extended with e.g. the SW cloud extending over more than $2^{\rm o}$ while only the central 20' could be seen in the synthesis observations (Fig. 2). In fact, the gas nearly encircles the optical with the two main concentration aligned with the direction of the proper motion.

**Figure 5:** A
$4^{\rm o} \times 4^{\rm o}$ field around Sculptor from the HIPASS survey. The contours are 1.5, 3.0, 6.0, 12.0 & 24.0

x 10¹⁸ cm^-2. The arrow indicates the position angle of the measured proper motion. The moment maps were derived for the velocity range [59.3, 138.4] kms^-1.
$\begin{figure} \begin{center} \epsfxsize=4.0in \leavevmode \epsffile{fig5.ps}\end{center}\end{figure}$

Since the detected gas covers a very large area and since it is at low velocities, very close to the velocities seen for High Velocity Clouds (HVC) and for MS gas, it is important to be able to view a very large area if one wants to disentangle those different velocity components. Fig. 6 shows an even larger area of

$8^{\rm o} \times 8^{\rm o}$ around Sculptor, again obtained with the PMS. The first striking feature is the large amount of gas to the south of Sculptor. The gas to the SW is the HI disk of the Sculptor Group late-type spiral NGC 300 (Puche, Carignan & Bosma 1990) while the gas to the SE is believed to be a long HI tail also associated with NGC 300 since it connects very smoothly with the eastern section of the main body of HI surrounding NGC 300. Mathewson, Cleary & Murray (1975) claimed that this could be the remains of the original concentration of gas from which NGC 300 formed. A larger area will be needed to see if the clouds at 116 and 122kms^-1to the west are part of a larger complex.

**Figure 6:** A
$8^{\rm o} \times 8^{\rm o}$ field around Sculptor from the HIPASS survey. The contours are 0.2, 0.4, 0.8, 1.6 & 3.2

x 10¹⁹ cm^-2. Velocities of the different HI components are indicated.
$\begin{figure} \begin{center} \epsfxsize=4.0in \leavevmode \epsffile{fig6.ps}\end{center}\end{figure}$

So, in the region of Sculptor, it is clear that large areas have to be looked at with an instrument sensitive to the large scales if one wants to be able to disantengle the gas associated with the dSph from the Local gas (HVC's), the MS gas, and from the Sculptor Group gas which all have very similar radial velocities. This is not only the case for Sculptor but also for most LG dSph galaxies.

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