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Diffuse Radio Recombination Line emission on the Galactic plane between l=36 to 44 degrees

Marta Alves
University of Manchester, UK

The study and understanding of the Cosmic Microwave Background (CMB) is a major goal in modern astronomy. Galactic free-free emission is principal foreground of the CMB. A full-sky template of this component is increasingly important for the upcoming high-sensitivity and high resolution experiments, such as the recently launched Planck satellite.
The H_alpha line is a good tracer of the free-free emission and it has been used to produce all sky-maps. It gives a good indication at intermediate and high latitudes, but becomes unreliable on the Galactic plane due to the high absorption, so a radio technique is required in this region.
Radio Recombination Lines (RRLs) serve this purpose and are used to determine the Emission Measure unambiguously along the plane of the Galaxy. We use the HI Parkes All-Sky Survey, which includes 3 RRLs (H166_alpha, H167_alpha and H168_alpha) to map for the first time the free-free emission on the Galactic plane covering the region l=36 to 44 degrees and b=-4 to 4 degrees.
Well-known HII regions are identified as well as diffuse emission and a free-free map of this region is recovered. The RRL Galactic latitude distribution has a half power width of about 1.5 degrees. These results can now be combined with low frequency data to separate the free-free and synchrotron foregrounds and also quantify the anomalous dust contribution using WMAP or Planck data.

2009 November 09, 13:30

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