Kinematics and Structure of the Starburst Galaxy NGC 7673

Abstract

The morphology and kinematics of the luminous blue starburst galaxy NGC 7673 are explored using the WIYN (Wisconsin-Indiana-Yale-NOAO) 3.5 m telescope. Signs of a past kinematic disturbance are detected in the outer galaxy; the most notable feature is a luminous ripple located 155 from the center of NGC 7673. Subarcsecond imaging in B and R filters also reveals red dust lanes and blue star clusters that delineate spiral arms in the bright inner disk, and narrowband Hα imaging shows that the luminous star clusters are associated with giant H II regions. The Hα kinematics measured with echelle imaging spectroscopy using the WIYN DensePak fiber array imply that these H II regions are confined to a smoothly rotating disk. The velocity dispersion in ionized gas in the disk is σ ~ 24 km s-1, which sets an upper boundary on the dispersion of young stellar populations. Broad emission components with σ ~ 63 km s-1 found in some regions are likely produced by mechanical power supplied by massive, young stars; a violent starburst is occurring in a kinematically calm disk. Although the asymmetric outer features point to a merger or interaction as the starburst trigger, the inner disk structure constrains the strength of the event to the scale of a minor merger or weak interaction that occurred at least an outer disk dynamical timescale in the past.