Publ. Astron. Soc. Aust., 1999, 16, 35–7 .
The HI Parkes Zone of Avoidance Shallow Survey
P. A. Henning1, L. Staveley-Smith2, R. C. Kraan-Korteweg3 and E. M. Sadler4
1 Institute for Astrophysics, University of New Mexico, Albuquerque, NM, 87131, USA [email protected] 2 Australia Telescope National Facility, CSIRO, PO Box 76, Epping, NSW 1710, Australia [email protected] 3 Departamento de Astronomia, Universidad de Guanajuato, Guanajuato, GTO, CP 36000, Mexico [email protected] 4 School of Physics, University of Sydney, NSW 2006, Australia [email protected] Received 1998 November 2, accepted 1999 January 22
Abstract: The HI Parkes Zone of Avoidance Survey is a 21 cm blind search with the multibeam receiver on the 64-m radiotelescope, looking for galaxies hidden behind the southern Milky Way. The rst, shallow (15 mJy rms) phase of the survey has uncovered 107 galaxies, two-thirds of which were previously unknown. The addition of these galaxies to existing extragalactic catalogues allows the connectivity of a very long, thin lament across the Zone of Avoidance within 3500 km s 1 to become evident. No local, hidden, very massive objects were uncovered. With similar results in the north (the Dwingeloo Obscured Galaxies Survey) our census of the most dynamically important HI-rich nearby galaxies is now complete, at least for those objects whose HI pro les are not totally buried in the Galactic HI signal. Tests are being devised to better quantify this remaining ZOA for blind HI searches. The full survey is ongoing, and is expected to produce a catalogue of thousands of objects when it is nished.
Keywords: zone of avoidance—surveys—galaxies: HI—large-scale structure of universe
1 Introduction the Dwingeloo radiotelescope (Henning et al. 1998; The dust and high stellar density of the Milky Way Rivers, Henning & Kraan-Korteweg 1999, this issue obscures up to 25% of the optical extragalactic sky, p. 48). creating a Zone of Avoidance (ZOA). The resulting incomplete coverage of surveys of external galaxies 2 The Shallow Survey leaves open the possibility that dynamically impor- tant structures, or even nearby massive galaxies, 2.1 Observing Strategy remain undiscovered. The HI Parkes ZOA survey covers the southern Careful searches in the optical and infrared wave ZOA (212 l 36 ; |b| 5 ) over the velocity bands can narrow the ZOA (see Kraan-Korteweg range cz = 1200 to 12700 km s 1. The multibeam & Woudt 1999, this issue p. 53) but in the regions receiver is a focal plane array with 13 beams arranged of highest obscuration and infrared confusion, only in a hexagonal grid. The spacing between adjacent radio surveys can nd galaxies. The 21 cm line of beams is about two beamwidths, each beamwidth neutral hydrogen (HI) passes readily through the being 14 arcmin. The survey is comprised of obscuration, so galaxies with su cient HI can be 23 contiguous rectangular elds which are scanned found through detection of their 21 cm emission. Of parallel to the galactic equator. Eventually, each course, this method will miss HI-poor, early-type patch will be observed 25 times, with scans o set by galaxies, and cannot discriminate HI galaxies with about 1 5 arcmin in latitude. The shallow survey redshifts near zero velocity from Galactic HI. discussed here consists of two scans in longitude Here we describe an HI blind survey for galaxies in separated by b = 17 arcmin, resulting in an rms the southern ZOA conducted with the new multibeam noise of about 15 mJy, equivalent to a 5 HI mass 6 2 receiver on the 64-m Parkes telescope. A survey of detection limit of 4 10 dMpc M (for a galaxy HI galaxies in the northern ZOA is underway with with the typical linewidth of 200 km s 1).
᭧Astronomical Society of Australia 1323-3580/99/010035$05.00 36 P. A. Henning et al.