A Blind HI Survey in the Great Attractor Region.

S. Juraszek
, PASA, 16 (1), in press.

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Introduction

Visual identification of galaxies is possible down to Galactic latitudes as low as 5 $^\circ$ (e.g. Kraan-Korteweg et al. 1994, Woudt et al. 1998). However, within 5 $^\circ$ of the Galactic equator, observations at all infrared and optical wavelengths become very difficult and ultimately confusion-limited (Lu et al. 1990). In this latitude range, neutral hydrogen (HI) observations at $\lambda$ 21 cm have been used with considerable success. The two main limitations in detecting galaxies using this method come from the HI and continuum emission from our Galaxy. The local HI emission covers a narrow velocity range of -100 to +100 km s^-1 and in this range extragalactic HI may be masked. While continuum sources cover the entire velocity range of the observation and mask galaxies by reducing sensitivity, in general they only cover very small areas of sky. The new Parkes 21 cm multibeam receiver (Staveley-Smith et al. 1997) has an array of 13 feed horns (each having two receivers with orthogonal linear polarisations) mounted hexagonally in the prime focus of the Parkes¹ 64 m telescope. The system has a beamwidth of 14.3' (FWHP). The Parkes HI multibeam instrument is ideal for surveying large areas in a relatively short time with a sensitivity previously unavailable. We present some of the first results of a blind HI survey for galaxies in the direction of the Great Attractor. The surveyed region covers Galactic longitudes 308 $^\circ$ to 332 $^\circ$ and Galactic latitude $\vert b\vert\leq$ 5 $^\circ$ with a velocity range of -1200 to +12700 km s^-1. This survey has detected HI in 42 galaxies.

**Figure 1:** (Left) The Parkes multibeam HI contours are shown overlayed on the Digitized Sky Survey (DSS) image of a previously identified galaxy J1514-52 (ZOAG G323.59-04.04). (Right) The line profile of J1514-52 shows the classical double horn profile expected for a nearby HI rich edge-on spiral galaxy.
$\begin{figure} \begin{center} \psfig{file=z1514-52.eps,height=10cm} \end{center} \end{figure}$

**Figure 2:** (Top) A narrow, single-peak, velocity profile of galaxy J1532-56, which is at approximately the same distance as J1514-52. The HI profile appears more like that expected for a face-on or an irregular galaxy. This galaxy has not been detected previously. The optical image of this region shows only foreground stars. (Below Left) The HI contours from the Australia Telescope Compact Array¹ (ATCA) follow-up observations (Staveley-Smith et al. 1998) are plotted on a column density image from the Parkes multibeam. The ATCA shows unexpected amounts of structure suggesting it is an interacting system of two galaxies. (Below Right) The HI contours have been plotted on an IRAS Galaxy Atlas (IGA) image at 60 $\mu$ m (Cao et al. submitted). This IRAS data has been super-resolved to 1-2 arcmin resolution.
$\begin{figure} \begin{center} \psfig{file=z1532-56.eps,height=14cm} \end{center} \end{figure}$

**Figure 3:** (Top) The distribution on the sky of the 42 HI detected galaxies and (Bottom) the velocity distribution histogram with a bin size of 500 km s^-1. The velocities (cz) calculated have been corrected for Local Group Motion.
$\begin{figure} \begin{center} \psfig{file=zhiplot.eps,height=9cm} \psfig{file=zhihist.eps,height=8cm} \end{center} \end{figure}$

**Figure 4:** The HI detected galaxies ( $\circ$ ) are plotted over a distribution of optically identified galaxies ( $\cdot$ ) with velocities in the range 0 to 6000 km s^-1 (Durand et al. 1994). The large area of sky shows the connection of the detected galaxies to the large scale structure. Filled circles denote galaxies with optical counterparts from the above database.
$\begin{figure} \begin{center} \psfig{file=zall6000.eps,height=14cm} \end{center} \end{figure}$

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Contents Page: Volume 16, Number 1

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Introduction