Can the rotation of the dark matter halo of our galaxy be detected through its effect on thecosmic microwave background polarization?

Abstract

The proposition that dark matter halos possess angular momentum, though widelyaccepted, is a theoretical prediction which has, to date, not been observationally verified.The gravomagnetic field produced by a rotating gravitating object is possibly the onlydirect consequence of the angular momentum of dark matter halos. The gravitationalFaraday rotation produced by the dark matter halo of our galaxy is present inall astronomical observations. A detection of the imprint of this effect on theall-sky cosmic microwave background radiation polarization pattern would directlyprobe the angular momentum of the dark matter halo of our galaxy. We havecalculated the expected gravitational Faraday rotation which turns out to be a(vc/c)3 effect,vc beingthe rotational speed of our halo. The predicted gravitational Faraday effect rotation angles are much lessthan 1′′, implying that this effect, though present, is too small to be detected.