EDP Sciences
Free access
Volume 442, Number 2, November I 2005
Page(s) 455 - 459
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20052743

A&A 442, 455-459 (2005)
DOI: 10.1051/0004-6361:20052743

The large asymmetric HI envelope of the isolated galaxy NGC 864 (CIG 96)

D. Espada1, A. Bosma2, L. Verdes-Montenegro1, E. Athanassoula2, S. Leon1, J. Sulentic3 and M. S. Yun4

1  Instituto de Astrofísica de Andalucía, CSIC, Apdo. 3004, 18080 Granada, Spain
    e-mail: daniel@iaa.es
2  Observatoire de Marseille, 2 Place le Verrier, 13248 Marseille Cedex 4, France
3  Department of Astronomy, University of Alabama, AL 35487, USA
4  Department of Astronomy, University of Massachussetts, Amherst, MA 01003, USA

(Received 21 January 2005 / Accepted 23 June 2005 )

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 $\times$ 106 $M_\odot$) 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.

Key words: galaxies: spiral -- galaxies: structure -- galaxies: kinematics and dynamics -- galaxies: evolution -- radio lines: galaxies

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