Surveys in the North and South

The time is ripe for a full 21-cm survey of the ZOA. There is no other way to map large scale structure in the regions of highest optical obscuration, and infrared confusion. In the north, the Dwingeloo telescope is surveying the ZOA over the area , out to a redshift of 4000 km s. A quick, shallow (5 min/pointing) survey of the entire area has been completed, with the aim of finding very massive and/or nearby galaxies. Three objects were clearly detected, the nearest being the barred spiral dubbed "Dwingeloo 1", first reported by Kraan-Korteweg et al. (1994.) The telescope is currently conducting a deeper survey (1 hr/pointing) of the same area, to uncover normal spirals to the survey redshift limit, and local dwarfs. Figure 2 shows the HI mass detection limit as a function of distance for the deep survey, calculated from the rms noise per pointing of 40 mJy.

 


Figure 2: The sensitivity to HI mass as a function of distance of the Dwingeloo Obscured Galaxies Survey for the deep phase (one hour/pointing), for galaxies of three representative linewidths.

Extrapolating from the HI mass function derived from the 300-ft survey, and the consistent results from an Arecibo survey (Schneider 1996) we estimate the Dwingeloo survey will uncover about 100 previously unknown galaxies. New galaxies are being cataloged now, and when obscuration allows, optical follow-up work is being done with the University of New Mexico's 24" telescope at Capilla Peak, with plans for deeper work with the 3.5m at Apache Point. When a larger sample has been collected, HI synthesis images will be obtained.

The biggest leap forward will occur in the south, with the advent of the multibeam system. Previous surveys have struggled to find dozens of galaxies, Dwingeloo will do somewhat better, but the multibeam ZOA survey promises the detection of thousands, owing to the excellent sensitivity and broad velocity coverage. (These estimates are based on HI mass functions derived from relatively tiny samples.) The area covered ( with redshift limit of 12,700 km ) spans many structures of interest, including the southern crossing of the Local Supercluster, the probable connection between the Hydra-Centaurus supercluster and the Pavo-Indus-Telescopium supercluster, and not least of all, the region of the rich cluster A3627 which lies only 9 from the predicted center of the Great Attractor (see the contribution by R.C. Kraan-Korteweg in this volume for the state of her optical ZOA survey). The true extent of these and other dynamically important structures, and the presence of any heretofore undiscovered local galaxies, will be uncovered by the multibeam survey.

© Copyright Astronomical Society of Australia 1997