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Minutes of the talk on:
      Using the Parkes Multbeam to Search for HVC Analogs

D.J. Pisano (ATNF)

A more detailed version of this talk by the speaker is available in HTML, PDF or PPT format.

The HVCs around the Milky Way include the big complexes as well as the compact HVCs. Blitz et al. (1999) and Braun & Burton (1999) have suggested that some HVCs have median distances of 500 kpc to 1 Mpc and HI masses of 106 - 7 solar masses. In order to fine potential analogs of the latter, we need comparable sensitivity and spatial coverage.

Simulations of galaxy formation, e.g. Klypin et al. (1999), predict large numbers of satellites in Local Group analogs. These objects have velocity widths less than 20 km/s, so high velocity resolution is needed.

Survey of nearby loose groups

Our approach is to look in loose groups that are similar in characteristics to the Local Group. Typically, loose groups contain a few large galaxies and tens of smaller ones, with the large galaxies typically separated by 100-200 kpc. The total extent of the group is characteristically about 1 Mpc. Most interesting are groups dominated by spirals which do not show signs of significant interactions or X-ray emission.

Results so far

In LGG 93, we have 4 new detections. One is clearly associated with an ESO-LV galaxy. For the others, we cannot yet tell which is the obvious detection because there are several NED objects in the beam. We will do ATCA followup for confimation.

It is very important to understand sensitivities because of the narrowness of the velocity widths. A plot of w(20) versus the integrated flux S(int) for our detections suggests that we have not detected anything below 10 sigma (maybe higher!) or 50 km/s. This dependence may be related to the current stage of our data processing. Clearly we need to do more work on this.

How can ALFA help?

Consider a comparison of the Parkes Multibeam with ALFA:

System Gain Tsys # beams
Parkes MB 0.67 K/Jy 21 K 13
AO/ALFA 8 K/Jy 30 K 7
Hence, with ALFA, we can map more groups and/or more distant groups, thus achieving better statistics.

But note that the poorer Tsys degrades Arecibo's benefit. It is very important to try to achieve the best possible performance in terms of gain and Tsys.

ALFA will certainly allow the detection of lower HI masses. Lower mass limits can better constrain HVC models.

next up previous
Next: Sunday pm #1 Up: Minutes of the 1st Previous: HVCs

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