Next: Sunday pm #1
Up: Minutes of the 1st
Previous: HVCs
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.
- Sensitivity to 106 - 7 solar masses.
- High velocity resolution
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.
- To date, we have surveyed 4 nearby groups already, are soon to do 5th. Data for 3 have been
reduced. All of our target groups are at about 10 Mpc.
- LGG 93, 180 and 478 at distances of order 10 Mpc.
- Area about 25-35 sq deg/group.
- High spectral resolution of 1-3 km/s.
- Mass sensitivity for 3.3 km/s: is 5 to 8 x 105 solar
masses (1 sigma). Should be good for
to 
solar masses for reasonable velocity widths.
- Regions were scanned in both RA and Dec.
- 42 minutes/beam;
- Basketweave technique lets us visit the same point many many times, hence
good for interference excision.
- Observations randomized as much as possible.
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.
- Detections were identified by searching by eye cuts through the cubes.
- An ATCA mosaic around the region confirms our detections.
- It will also allow us to look for HVC's nearby on smaller scale.
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 |
- ALFA can map the same area 2 times faster than Parkes.
- ALFA can map the same area 2 times deeper than Parkes in same time.
Hence, with ALFA, we can map more groups and/or more distant groups,
thus achieving better statistics.
- ALFA's smaller beam will help a lot for optical identification.
- Resolution is AO's big advantage.
- At distances to 50 Mpc, ALFA will achieve the same resolution as
HIPASS gets at 10 Mpc.
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: Sunday pm #1
Up: Minutes of the 1st
Previous: HVCs
This page created and maintained by Karen Masters,
Kristine Spekkens
and Martha Haynes.
Last modified: Tue Apr 29 08:15:29 EDT 2003