1998AJ....115.1433E

NGC 4485 and NGC 4490 are closely interacting spiral galaxies in the NGC 4631 Group, separated by a projected distance of 7.7 kpc. Images in the B and I bands were obtained with the Burrell Schmidt telescope at Kitt Peak National Observatory in order to study star-forming regions in their tidal features, including a previously undetected faint tail whose color matches that of the outer disk in NGC 4490. A comparison of the tidal morphology with published simulations suggests that this is a prograde encounter with perigalacticon about 4x10⁸ yr ago. This time is approximately the age of the youngest regions in the tail, based on a comparison of observed B - I colors with evolutionary models. Calculations of the Q instability parameter using a rotation curve derived from published H I observations support the conclusion that the tail is currently stable against star formation.