ON THE ORIGIN OF THE SOUTHWEST Hα REGIONS OF THE SPIRAL GALAXY NGC 3367

摘要

New narrow-band, continuum-free, Hα, and broadband R and I imaging data from the barred galaxy NGC 3367 are presented. Our Hα observations indicate that there is Hα almost all over the disk of the galaxy, and there are no particular signs of either nuclear or outer rings. Strong Hα emission is detected from the compact nucleus and from different sources in the disk. In particular, there are H II regions at the ends of the stellar bar and in the inner spiral arms. Also, and very strikingly, a string of Hα emission sources spanning almost 180°, from southeast to northwest, is observed in the southwest region of the galaxy, at an almost constant radius from the center. The string is located outside the stellar bar and does not belong to any particular spiral arm. There are several possible interpretations regarding the origin of these Hα knots (i.e., due to an outer Lindblad resonance ring, to the interaction of NGC 3367 with a hot intergalactic medium, or to a direct impact with a neighbor), but we favor the possibility that the string is due to an off-center impact by an intruder. This scenario can also explain the emission from the compact nucleus and is consistent with the expected lifetimes of the Hα knots and the kinematic timescales for an induced ring by an intruder. The string of Hα sources is probably evidence of having cloud overlap, which has triggered new massive star formation.