COUNTERROTATING GASEOUS DISKS IN NGC-4826

Observations are presented of the system of nested counterrotating gas eous disks discovered in NGC 4826. Imaging spectroscopy in neutral hyd rogen has been done using the VLA and the WSRT. Broad-band optical ima ges in B, V, and I as well as narrow-band images in H alpha and [S II] have been obtained at the KPNO. Partial imaging along two position an gles in the CO (3-->2) transition was carried out at the JCMT. All com ponents for which kinematic data exist (neutral, molecular and ionized gas as well as a stellar component) within a radius of 1 kpc share th e same sense of rotation. The inner gas disk has an extremely high gas surface density (greater than 50 M(.) pc(-2)) and high star formation rate. This inner disk is bounded by an annular region of low gas surf ace density with faint, diffuse Ha emission detected between 1 and 2.8 kpc radius. An outer gas disk is detected in neutral hydrogen extendi ng from 1.5 to 11 kpc radius at a surface density of similar to 0.5 M( .) pc(-2). The H I kinematics indicate counterrotation of this compone nt relative to the inner galaxy at an identical kinematic position ang le and inclination. A luminous stellar disk dominates the optical cont inuum emission and extends out to a radius of 5.5 kpc with substantial surface brightness. Recent optical spectroscopy has shown that the ou ter stellar disk shares the kinematics of the inner galaxy. It seems l ikely that the stellar disk decelerates the tenuous, co-planar, counte rrotating outer gas disk through a strong interaction with its stellar mass loss. The observed system of nested, counterrotating gaseous dis ks may have arisen in the antiparallel spin merger of a gas poor spira l with a star-poor dwarf, each containing a few times 10(8) M(.) of ga s. An alternate formation scenario calls for the continuous accretion of a few times 10(8) M(.) of antiparallel spin gas. The interaction of gaseous disks with stellar mass loss may also play an important role in the evolution of polar ring galaxies as well as more generally in b ulge-dominated galaxies.