New Light and Shadows on Stephan’s Quintet

We present deep broad-band R and narrow-band Halpha images of Stephan'sQuintet. The observations in the R band show that the diffuse halo of theStephan's Quintet is larger than previously thought and extends out to NGC7320C. However, we have not found emission connecting NGC 7331 and NGC 7320 toR ~ 26.7 mag/arcsec^2 (at more than 3-sigma level), so there is no directevidence up to this limiting magnitude of a relation between the peculiarkinematical structure found in NGC 7331 and an ongoing or past interactionbetween this galaxy and NGC 7320. The Halpha emission at high-velocity(6000-7000 km/s) is distributed in a diffuse structure running NS between NGC7319 and NGC 7318B and in some other more concentrated features. Some of theseare located in the tidal tails produced by the interaction between the galaxiesof the group. With the Halpha images we have made a two-dimensional velocitymap which helps to identify the origin of each structure detected. This mapdoes not show features at intermediate velocities between the high- andlow-redshift members of the group. This is in agreement with the standardscenario in which the apparent proximity of NGC 7320 to the rest of thegalaxies of the Quintet is merely a projection effect. The only point which isunclear in this interpretation, is an Halpha filament which is seen extendingthroughout NGC 7320 with velocity at 6500 km/s instead of the 800 km/s expectedfor this galaxy.Comment: Accepted for publication in Astrophys.