Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2011-01-13
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
7 pages, 5 figures, 1 table, accepted to MNRAS after revision
Scientific paper
Polarised radio synchrotron emission from interstellar, intracluster and intergalactic magnetic fields is affected by frequency-dependent Faraday depolarisation. The maximum polarised intensity depends on the physical properties of the depolarising medium. New-generation radio telescopes like LOFAR, SKA and its precursors need a wide range of frequencies to cover the full range of objects. The optimum frequency of maximum polarised intensity (PI) is computed for the cases of depolarisation in magneto-ionic media by regular magnetic fields (differential Faraday rotation) or by turbulent magnetic fields (internal or external Faraday dispersion), assuming that the Faraday spectrum of the medium is dominated by one component or that the medium is turbulent. Polarised emission from bright galaxy disks, spiral arms and cores of galaxy clusters are best observed at wavelengths below a few centimeters (at frequencies beyond about 10 GHz), halos of galaxies and clusters around decimeter wavelengths (at frequencies below about 2 GHz). Intergalactic filaments need observations at meter wavelengths (frequencies below 300 MHz). Sources with extremely large intrinsic $|RM|$ or RM dispersion can be searched with mm-wave telescopes. Measurement of the PI spectrum allows us to derive the average Faraday rotation measure $|RM|$ or the Faraday dispersion within the source, as demonstrated for the case of the spiral galaxy NGC 6946. Periodic fluctuations in PI at low frequencies are a signature of differential Faraday rotation. Internal and external Faraday dispersion can be distinguished by the different slopes of the PI spectrum at low frequencies. A wide band around the optimum frequency is important to distinguish between varieties of depolarisation effects.
Arshakian Tigran G.
Beck Rainer
No associations
LandOfFree
Optimum frequency band for radio polarisation observations does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Optimum frequency band for radio polarisation observations, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optimum frequency band for radio polarisation observations will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-67111