Daily Image
07-05-2010
Hoog, Sammy, kijk omhoog
| Submitter: | Marijke Haverkorn |
| Description: | "Hoog, Sammy, kijk omhoog" is the famous text of a Dutch song by singer/songwriter Ramses Shaffy. Harvard graduate student Sui Ann Mao (with initials SAM), has diligently followed Shaffy's advice to "Up, Sammy, look up". As part of her PhD, Ann looked up with Westerbork to the north Galactic pole, trying to detect the vertical component of the Galactic magnetic field. Similarly, she used the Australia Telescope Compact Array to look to the southern Galactic pole for the field's southern counterpart. Ann observed 1033 polarized extragalactic sources to extract their rotation measure (RM), which is a measure of magnetic field. From these, she calculated that there is a very weak vertical magnetic field in the south, but no large-scale vertical field whatsoever in the north. The picture shows the northern and southern Galactic caps. The green symbols denote RMs of the point sources, and white asterisks are sources consistent with RM = 0. Filled and open symbols (i.e. positive and negative RM) indicate even by eye that there is very little or no uniform component here. The orange background is H-alpha intensity (from two surveys with different resolutions), which measures electron density. Studying the strength and direction of the vertical magnetic field on both sides of the Galactic plane sheds light on the origin of the Galactic magnetic field, and the workings of the dynamo that maintains it. With these results, Ann proves once again that reality cannot be captured in simple dynamo models. These observations and more detailed interpretations have just been published in Mao, Gaensler, Haverkorn, Zweibel, Madsen, McClure-Griffiths, Shukurov and Kronberg, 2010, ApJ 714, 1170. |
| Copyright: | Mao et al, 2010, ApJ 714, 1170 |
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