Thursday, 11 September, 1997 at 3pm

Stuart Ryder - Joint Astronomy Centre

"The Peculiar Rotation Curve of NGC 157"

ABSTRACT: "The results of a new HI, optical, and H-alpha study of the nearby spiral galaxy NGC 157 will be presented. Observations with both the C- and D-arrays of the VLA have been combined to reveal a large-scale, ring-like structure in the neutral hydrogen underlying the optical disk, together with an extended, low surface density component going out to nearly twice the Holmberg radius. Beginning just inside the edge of the star-forming disk, the line of nodes in the gas disk commences a 60 degree warp, while at the same time, the rotation velocity drops by almost half its peak value of 200 km/s, before leveling off again in the outer parts. While a flat rotation curve in NGC 157 cannot be ruled out, supportive evidence for an abrupt decline comes from the ionised gas kinematics, the optical surface photometry, and the global HI profile. A standard `maximum-disk' mass model predicts comparable amounts of dark and luminous matter within NGC 157. Alternatively, a model employing a disk truncated at 2 disk scale lengths could equally well account for the unusual form of the rotation curve in NGC 157."