High resolution 21 cm mapping of the Ursa Major Galactic cirrus: Power spectra of the high-latitude HI gas

¹ Institut d'Astrophysique Spatiale, Université Paris-Sud, Bât. 121, 91405 Orsay, France
² Canadian Institute for Theoretical Astrophysics, 60 St-George st, Toronto, Ontario M5S 3H8, Canada
³ Département de physique, de génie physique et d'optique, Observatoire du mont Mégantic, Université Laval, Sainte-Foy, Québec G1K 7P4, Canada
⁴ LERMA/LRA, CNRS-UMR 8112, École Normale Supérieure, 24 rue Lhomond, 75005 Paris, France

Corresponding author: M.-A. Miville-Deschênes, mamd@ias.u-psud.fr

Received: 8 January 2003
Accepted: 1 July 2003

Abstract

We present a power spectrum analysis of interferometric 21 cm observations of the Ursa Major high-latitude cirrus, obtained with the Dominion Radio Astrophysical Observatory (DRAO) of Penticton (Canada). These high-resolution data reveal the intricate structure of the diffuse Galactic Hi, at angular scales from 1 arcmin to 3 degrees. A filtering method based on a wavelet decomposition was used to enhance the signal-to-noise ratio of the data. The power spectra of the integrated emission and of the centroid velocity fields were used to deduce the three-dimensional (3D) spectral index of the density and velocity fields of the Hi cirrus. The spectral index is similar for the 3D density and velocity fields with a value of . Using the Leiden/Dwingeloo observations, this analysis was extended to the whole North Celestial Loop (which includes the Ursa Major cirrus), showing that the scaling laws prevail from 0.1 to 25 pc. The centroid velocity and integrated emission fields show moderate correlation, with a maximum cross-correlation value of 0.44.