S. Juraszek
, PASA, 16 (1), in press.
| Next Section: Discussion Title/Abstract Page: A Blind HI Survey Previous Section: Introduction | Contents Page: Volume 16, Number 1 |
Data Analysis & Results
This blind HI survey comprises data from 3 standard ZOA fields. Each standard field is 8
x 10 in size and has been scanned 4 times (when the ZOA Survey is completed this region will have been observed 25 times hence the data presented here is only 16% of the final ZOA Survey). This data has then been gridded together using specially developed aips++ routines (Barnes 1998). The data is Nyquist sampled (Staveley-Smith et al. 1998). The final data cube has an rms noise of 20 mJy beam-1, a gridded beam size of 15.5' and pixel size of 4' x 4', with a velocity resolution of 18 km s-1. The data cube was searched visually 3 times in different orientations to confirm identification and classification of candidate HI sources. After careful application of flux limits and selection criteria, we have a final catalogue of 42 HI detections. For all the detections we have found that the profiles exhibit either the classical double horn profile of an edge-on spiral galaxy (Figure 1) or a Gaussian profile of a face-on or irregular galaxy (Figure 2). We have found no HI galaxies in this region with negative velocities, indicating motion towards the Local Standard of Rest. We have attempted to identify these sources using various other catalogues. In our search, we have used both position and velocity information, to make galaxy identification. The two main catalogues that we have used in the process are WKK (Woudt et al. 1998) and the IRAS Point Source Catalog (Version 2, 1998, hereafter PSC). With a search radius of 6' we identified 15 galaxies, of which 6 have no redshift information, so their association is tentative. No further associations or identifications were found using NED2. Conservatively at least 60% of the galaxies that we find in the ZOA are new discoveries; this value will increase with the full sensitivity survey. The WKK catalogue allows us to comment on the morphology of some of the HI detected galaxies in our sample. We have been able to associate the following morphologies with our HI detections: 24% Spirals; 10% Barred Spirals; and 5% Ellipticals or Spiral bulges. This leaves at least 60% with no observable Hubble morphology. Morphology classification in the ZOA is difficult due to the varying levels of extinction caused by our Galaxy. Foreground absorption may obscure the outer parts of spiral galaxies leaving only the bulge distinct. The IRAS PSC together with the IRAS Galaxy Atlas (Cao et al. submitted) was used to obtain infrared flux densities (not colour-corrected) and further associations. 12% of the HI galaxies were associated with IRAS sources which have no optical counterparts in the WKK catalogue. We have used selection criteria to minimise the possibility of chance alignment between a HI galaxy and a Galactic IRAS source. The Parkes telescope beam at 21cm resolved 4 of the galaxies for which we have calculated HI diameters, measured at the 50% peak brightness level. The HI diameters are in the range 50 to 110 kpc. Using this result, an indicative total mass was calculated ranging from 2 x 1010 to 2 x 1011 M
. The range in velocity within which we found galaxies is 100 to 6000 km s-1. Although this reflects the sensitivity limit of the data, it does show that there are no unusually HI-rich galaxies within the fiducial velocity range of the Great Attractor. The range of HI masses is 
5 x 107 to 2 x 1010 M, where we have used H
= 75 km s-1 Mpc-1. Figure 3 shows the distribution of our 42 galaxies in Galactic coordinates and in velocity. We do detect an over-density at 3000 to 4000 km s-1. Further observations are required to determine the precise over-density of the region. We also show the HI detected galaxies on a plot of optically identified galaxies (Durand et al. 1994) to show the connectivity of large scale structures in the local universe (Figure 4). For the first time we have a clear view of the continuation of this large scale structure across the ZOA. | Next Section: Discussion Title/Abstract Page: A Blind HI Survey Previous Section: Introduction | Contents Page: Volume 16, Number 1 |
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