The large asymmetric HI envelope of CIG 96 (2005)

Scientific Results

The large asymmetric HI envelope of CIG 96

We have also observed 12 galaxies at the VLA, selected to have asymmetric HI profiles in order to understand the origin of the asymmetries in isolated galaxies. One of these galaxies (CIG 96 = NGC 864)  is particularly  interesting due  to the large level  of asymmetry in its HI distribution. 

Fig. 1 HI column density distribution (left) and velocity field (right) of NGC 864 and its companion, superimposed on the optical POSS2 red band image. The contour levels are: 5, 12, 24, 37, 49, 61, 73, 86, 98, 110 and 122 x 1020 cm-2. The velocity contours go from 1465 to 1660 km s-1 in intervals of 15 km s-1, and are labeled each 30 km s-1. The beam size of 49″.8 x 46″.2 is shown in the upper left of all panels.

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) = 5×106Mo) 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. All these results have been presented in the PhD of D. Espada.


Espada, 2006 PhD
PDF File Espada et al. 2005