CGPS News: Volume 18

CGPS News Volume 19
Nouvelles du RCPG Volume 19
Dec / déc 2001

From Harvard to Penticton: 50 Years of HI

Charles Kerton


From October 20th - 25th astronomers from all over the world gathered in Penticton to celebrate the 50th anniversary of the first detection of the 21-cm line from atomic hydrogen and to discuss current research and future developments in the field. The conference was divided into two roughly equal parts focusing on Galactic and extragalactic research with a lively panel discussion wrapping up each session. The research presented covered the entire universe - from a presentation on local HI features by Harold Weaver to a review by Paolo Tozzi on the potential of radio observations to shed some light on the "dark ages" era of our universe. It wasn't all work though! The conference banquet was well attended and Gart Westerhout gave a very entertaining talk on the early days of HI research. Attendees were also able to tour DRAO, sample some fine local beverages, and see some of the exciting new results from the IGPS along with a close-up look the work being done on the Canadian Large Adaptive Reflector.

A proceedings of the conference, including transcripts of the two panel discussions, is currently being prepared by Tom Landecker, Russ Taylor and Tony Willis. If you were unable to attend the meeting the link below will take you to a page where you can peruse the various talk and poster abstracts.

Seeing Through the Dust Abstracts

CGPS2 Observing Update

Andrew Gray

Observing for CGPS2 continues to go well. At the time of writing (Dec. 10) we have collected data for 69 of the 181 fields required. This includes 57/110 longitude extension fields, 12/68 latitude extension fields and 0/3 fields needed to improve imaging near Cyg A. Observing continues at a rate that is adequate to allow us to complete the project on time.

New IGPS Postdoctoral Fellow at Western

Shantanu Basu

A new IGPS Postdoctoral Fellow, Dr. Takahiro Kudoh, will be arriving at Western in January 2002. Dr. Kudoh comes to us from his present position of Research Fellow at the Astronomical Data Analysis Center of the National Astronomical Observatory, Japan.

Dr. Kudoh is one of the world's leading experts on the modeling of MHD flows in astrophysics. He has extensive experience in this field and has worked on a variety of problems across the landscape of astrophysics. He has gained notoriety for his work on the acceleration and collimation of astrophysical jets by magnetic forces. This work has clarified the relative roles of magnetic pressure and the magneto-centrifugal effect in the acceleration of jets, and shown that toroidal magnetic fields can indeed collimate jets. His interests on the galactic scale have also led him to conduct simulations on a magnetic origin for the Galactic-Ridge X-ray emission. He has also developed solutions for magnetized winds from rapidly rotating stars, MHD accretion flow onto a black hole, and recently developed some impressive models of the magnetic launching of spicules in the solar atmosphere. He has also developed his own MHD numerical code, which is specially suited to modeling magnetic-pressure dominated plasmas. There is no doubt he will contribute significantly to the numerical modeling of ISM phenomena performed by our group.

G91.8+2.0-114: Triggered star formation in the outer Galaxy?

Serge Pineault, Francois Cazzolato, & Vanessa Juneau

As part of a summer project, undergraduate student Vanessa Juneau, under the joint supervision of Serge and Francois, established a list of potential stellar wind (SW) candidate sources on the basis of their IR colors. A total of 59 candidates were found in the area covered by the CGPS Phase I. A subset of the available CGPS mosaics were then inspected for tell-tale evidence of SW action (cavities, bubbles, shells, rings).

One of the most interesting structures found is a large HI shell at a velocity of about - 114 km/s centered near (l,b) = (91.8, 2.0) (see figure). A flat rotation curve model puts this shell at a distance of 15 kpc, galactocentric radius 17 kpc and implies a diameter of 400 pc. Attention was drawn to this shell by the presence of three associated infrared SW candidate sources. One of these (the rightmost one on the figure) is associated with the HII complex BG 2107+49 studied by Paul van der Werf and Lloyd Higgs [AA, 235, 407 (1990)]. Of the remaining two, the lower-latitude one is of particular interest as it seems to lie itself within a smaller HI cavity projected onto the south-southeast part of the large HI shell. Interestingly enough, no large-scale continuum features are seen either in the radio at 1420 MHz or in the infrared at 60 microns. However a small but extended (about 6 arcmin in diameter) and relatively faint object (G91.8+1.0) is seen projected onto the south-southwest periphery of the HI shell.

Figure 1. HI Shell. Infrared SW candidates are indicated by the crosses.

Can this large shell be the result of a distant OB association? Is the smaller HI cavity produced by the wind of a star whose formation was triggered by the large shell? Is G91.6+1.0 a result of the interaction of the large shell with its surrounding interstellar medium? These questions and others are currently being pondered by Francois to whose Ph.D. project this object has been added as a region where sequential star formation has possibly taken place. The large distance of the shell is in stark contrast to the relatively nearby Cas OB7 association which has already been the subject of Francois' attention.

[NOTE: As this research involves a Ph.D. student, this item is added to the graduate student project registry. ]

Infrared Excess in the CGPS - Evidence of Molecular Hydrogen?

Kevin Douglas

In early December I spent a very productive week at the DRAO working on my PhD thesis research, which is to look for traces of diffuse gas, possibly molecular hydrogen, untraced by CO emission. My visit to DRAO coincided with the release of the MG1 and MG2 HI datacubes, which fortuitously happened to be the last remaining mosaics which overlap with the FCRAO Outer Galaxy Survey. This meant that the entire region in which I was interested was available to me for the first time in all the desired wavelengths. Thanks very much to Lewis Knee for churning those last two out for me! All of the images in this article show the entire FCRAO survey area convolved to 3 arcminutes.

The method used is to look for infrared excess features that are visible in the dust optical depth at 100 microns after subtracting the CO and HI maps from the same region of the sky. Assuming a constant gas-to-dust ratio, the dust optical depth (see Figure 1) should trace all the gas column density in the line of sight; the optical depth images are made by determining the dust temperature using the ratio of 60-to-100 micron IRAS images (see Figure 2).

Figure 1. Optical Depth Image. Regions with high dust temperatures (see Figure 2) have been blanked out.

Figure 2. Dust Temperatures. Dust temperatures are calculated using the IRAS 60/100 micron ratio.

Figure 3 shows the CO data from the FCRAO OGS. In Figure Four the CO has been subtracted from the optical depth map (Figure 1), and it is seen that many of the clumpy features have been successfully removed. The lack of CO data at longitudes > 142 results in a strange and ignorable pattern of blank regions and unsubtracted tau.

Figure 3. FCRAO OGS Data. Data have been integrated over all channels.

Figure 4. Removal of CO Contribution The contribution of CO to the optical depth has been subtracted (compare with Figure 1).

Figure 5 shows the integrated HI line data for the region. After subtracting this map in Figure 6, we can identify some excess features that will require further study. A very notable one is at l = 129, b = 4.

Figure 5. HI Data. Integrated HI data corresponding to OGS coverage.

Figure 6. Removal of HI Contribution The contribution of HI to the optical depth has been subtracted (compare with Figures 1 and 4).

The large amount of excess at longitudes around 110 is quite interesting. Is it deficient in HI and/or CO? Is the gas-to-dust ratio changing as we look more along the local arm? A comparison of the map with the 1420 MHz continuum data has shown no correlation of optical depth infrared excess features with ionized gas. Now that all the data I need are available, I will investigate these features at the best resolution I can in order to find out more about them.

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