UGC 3995: A close pair of spiral galaxies

UGC 3995 is a close pair of spiral galaxies whose eastern component hosts a Seyfert 2 nucleus. The object was selected for observation because a brigh t filamentary structure that apparently connects the nuclei of the two gala xies made it a good candidate to investigate a possible connection between galaxy interactions and active galactic nuclei. We present a detailed analy sis of this system using long-slit spectroscopy and narrowband (H alpha + [ N II] lambda lambda 6548, 6583), as well as broadband (B, R), imagine; and an archival Wide Field Planetary Camera 2 image. The component galaxies rev eal surprisingly small signs of interaction considering their spatial proxi mity and almost identical recession velocities, as the bright filament is p robably an optical illusion due to the superposition of the bar of the Seyf ert galaxy and of the spiral arms of the companion. The broadband morpholog y, a B-R color map, and a continuum-subtracted H alpha + [N II] lambda lamb da 6548, 6583 image demonstrate that the western component UGC 3995B is in front of the Seyfert-hosting component UGC 3995A, partly obscuring its west ern side. The small radial velocity difference leaves the relative motion o f the two galaxies largely unconstrained. The observed lack of major tidal deformations, along with some morphological peculiarities, suggests that th e galaxies are proximate in space but may have recently approached each oth er on the plane of the sky. The geometry of the system and the radial veloc ity curve at P.A. approximate to 106 degrees suggest that the encounter may be retrograde or, alternatively, prograde before perigalacticon. The parti al overlap of the two galaxies allows us to estimate the optical thickness of the disk of component B. We derive an extinction of approximate to 0.18 visual magnitudes in the interarm parts of the foreground galaxy disk, and greater than or similar to 1-1.5 visual magnitudes corresponding to the spi ral arms.