Asymmetry in High-Precision Global H [CSC]i[/CSC] Profiles of Isolated Spiral Galaxies

Abstract

New high signal-to-noise ratio 21 cm H I line proles have been obtained for 104 galaxies with the Green Bank 43 m telescope. The primary sample is composed of isolated spirals with no known optical companions within a 1 radius and a median ratio of optical diameter to beamwidth of 0.17. An e ort was made to ensure linearity of baseline tting and precise ux density calibration to better than 5%. Two quantitative measures of asymmetry are applied to assess the occurrence of lopsidedness in the global H I proles. In agreement with previous estimates, half the galaxies show signicant H I prole asymmetries. The lopsidedness cannot be explained by pointing o sets but, rather, must result from noncircular motions, confusion with unidentied companions within the telescope beam, or true distortions in the H I distribution.