January 2009: SPARO 2003 data used to probe magnetic field strength in molecular clouds

During the Antarctic winter of 2003, SPARO surveyed the large-scale magnetic fields of four Giant Molecular Clouds (GMCs). We have recently been able to set constraints on the characteristic magnetic field strength in GMCs by combining these SPARO results with (a) results for small-scale fields obtained using the Hertz instrument on Mauna Kea and (b) simulated polarization maps developed by theorists. We find that the total magnetic field energy (including both uniform and fluctuating components) is comparable to or greater than the kinetic energy corresponding to turbulent gas motions. Such strong fields are expected to play important roles in the star formation process that occurs in GMCs.

This work is described in a paper published in the Astrophysical Journal (see publications section of our web page). 

The Viper telescope was decommissioned in 2006.  Further exploration of the themes studied using SPARO will be possible using the BLAST balloon-borne submillimeter imager that has recently been converted into a polarimeter that we call BLAST-pol.  Our group is contributing to BLAST-pol.  To learn more about BLAST-Pol see the BLAST Web site or page 4 of the February 2009 Northwestern Research Newsletter

Fall 2006: SPARO results reported in SPIE Newsroom

Summer 2006: Results from SPARO's 2003 winter-over published in Astrophysical Journal

During SPARO's second South Pole winter-over in 2003, we mapped the large-scale magnetic fields of four star-forming interstellar clouds located in the Galactic disk. A paper recently published in The Astrophysical Journal describes our interpretation of these maps: Results of SPARO 2003: Mapping Magnetic Fields in Giant Molecular Clouds, by Hua-bai Li and collaborators.

At left we show a histogram of the inferred magnetic field directions, for all polarization measurements obtained in the four molecular clouds. The angles are given in Galactic coordinates, so that zero degrees is Galactic North-South, and 90 degrees is parallel to the Galactic plane. Our observations have revealed a tendency for the magnetic fields to be parallel to the Galactic plane. This has not been seen in previous studies of Giant Molecular Clouds, but past submillimeter polarimetric studies were not very sensitive to faint extended emission. SPARO's excellent sensitivity results from the superb observing site.

On the largest scales, the magnetic field in the Milky Way's disk is known to be azimuthal. Thus, the simplest explanation for the above correlation is that when a molecular cloud is formed from diffuse interstellar matter, the mean field direction is preserved. This places a constraint on theories that aim to explain how star-forming molecular clouds are themselves formed out of the diffuse interstellar Galactic gas.

Also available on this web page are the polarization maps and a sky coverage summary

Spring 2004: New publications by David Chuss and Tom Renbarger:

David Chuss has published a paper in the Astrophysical Journal discussing the morphology of the magnetic field in the central few tens of pc of the Galaxy. This paper is based primarily on new submillimeter polarimetric observations made with the Hertz instrument at the Caltech Submillimeter Observatory, but also makes use of information derived from the SPARO Galactic Center polarization map. To read Dave's paper go to the publications section of our web page.

Tom Renbarger has published a paper in the journal "Publications of the Astronomical Society of the Pacific" describing the design and performance of the SPARO instrument and also interpreting our Austral Winter 2000 observations of NGC 6334. To read Tom's paper go to the publications section of our web page.

Austral Winter 2003: SPARO is collecting data again!

The SPARO experiment was successfully set up at South Pole during January and February 2003 by a team from Northwestern (G. Novak, H. Li), Berkeley (W. Holzapfel, M. Daub, M. Lueker), Yerkes Observatory (R. Loewenstein, M. Thoma, M. Newcomb), and the University of New South Wales (P. Calisse).  We started the winter with 7000 gallons of liquid Helium on station.  We still had some work to do after station closing (pointing model and a few other details) so we did not get started on science until late March.  We got some good data in April, lost almost all of May due to a computer problem, and have had good success in June, with the good winter weather coming in.   Our main results so far are maps of the large-scale magnetic field morphologies in two star forming clouds: Carina, and "C4".   As of this writing (July 7), we have started observing our third star forming cloud, "C5".   Our goal is to produce magnetic field maps for a total of six star forming clouds in order to probe the role of magnetic fields in star formation.

Updates from Austral Summer 2002-2003 and Winter 2003:

Click here for past updates