The large asymmetric HI envelope of the isolated galaxy NGC 864 (CIG 96) Espada Fernández, Daniel Bosma, A. Verdes-Montenegro, L. Athanassoula, E. Leon, S. Sulentic, J. Yun, M. S. We present an HI synthesis imaging study of NGC 864 (CIG 96), a spiral galaxy well isolated from similarly sized companions, yet presenting an intriguing asymmetry in its integral HI spectrum. The asymmetry in the HI profile is associated with a strong kinematical perturbation in the gaseous envelope of the galaxy, where at one side the decay of the rotation curve is faster than Keplerian. We detect a small (M(HI) = 5 × 106 M_⊙) galaxy with a faint optical counterpart at ~80 kpc projected distance from NGC 864. This galaxy is probably not massive enough to have caused the perturbations in NGC 864. We discuss alternatives, such as the accretion of a gaseous companion at a radial velocity lower than the maximum. 2024-07-23T07:39:41Z 2024-07-23T07:39:41Z 2005 journal article Espada et al. 2005, A&A, 442, 455 https://hdl.handle.net/10481/93375 10.1051/0004-6361:20052743 eng http://creativecommons.org/licenses/by-nc-nd/3.0/ open access Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License EDP Sciences