MAGNETIC_MILKYWAY · The Magnetic Milky Way

The Magnetic Milky Way

STAPS is a survey of polarized radio emission over the entire southern sky. It was performed using the 64m single-dish telescope in Parkes, NSW, Australia. The complex scanning method and innovative use of receivers required software modification and development, and the presence of experienced observers at the telescope. In 2010, observations of this survey were finished after 149 nights of observations spread out over two years. Eight observing trips of each 17 to 23 nights were performed to finish the survey. Raw observational data are contaminated by unwanted signals: terrestrial radio emission leaking into the telescope, reflections of emission off the ground and off the telescope, and signal deformations due to the telescope hardware. The modeling and removal of such signals in STAPS is done using customized soft-ware developed by the project researcher and collaborators. The software performs the following steps: • contaminating signals from terrestrial radio emission are identified and removed; • telescope performance is characterized and corrected for, using calibrator sources; • scans are combined in a map making procedure to build a map of the whole sky; • overlapping scans are compared to assess and remove contaminating sources; • the absolute mean value of the polarized radio emission is determined and data corrected. Initial or final versions of each step in this software are now available. Preliminary processing and analysis of the maps has shown that the instrumental polarization characteristics of the survey are good and the data is of high quality. A preliminary first map is shown below. STAPS is the first-ever polarized radio survey of the southern sky in this broad frequency range (1300-1800 MHz). Broad frequency bands like this have only just become technically feasible, and are important since they allow better study of the variation of polarization with frequency. This frequency variability of magnetic fields is caused to a large extent by structure in magnetic fields in the Milky Way. This broad frequency range enables the new analysis tehnique Rotation Measure Synthesis that for the first time will give a three-dimensional image of galactic magnetic fields. The STAPS survey also enables science goals in other research areas. In particular, STAPS will be crucial for full exploitation of the Survey Science Project Polarization Sky Survey of the Universe's Magnetism (POSSUM) of the Australian Square Kilometre Array Pathfinder (ASKAP), a radio telescope under development in Western Australia. POSSUM will survey the Southern sky at the same frequency range as STAPS in much finer detail. However, it will lack information on large scales, which STAPS will provide. Interpretation of extended polarized structures in the sky such as interstellar clouds or large supernova remnants will not be possible without addition of STAPS data to POSSUM’s observations. Furthermore, all-sky radio surveys at different frequencies and resolutions have always been used by the community for a wide variety of science goals. Therefore, the expectation is thet STAPS will be a resource for researchers in a wide range of fields, including studies of the Galactic Center, synchrotron emission, supernova remnants, and external galaxies.

Data: CORDIS, © European Union