Kinematic Evidence of Minor Mergers in Normal S[CLC]a[/CLC] Galaxies: NGC 3626, NGC 3900, NGC 4772, and NGC 5854

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Abstract
BVRI and Hα imaging and long-slit optical spectroscopic data are presented for four morphologically normal and relatively isolated Sa galaxies, NGC 3626, NGC 3900, NGC 4772, and NGC 5854. VLA H I synthesis imaging is presented for the first three objects. In all four galaxies, evidence of kinematic decoupling of ionized gas components is found in the long-slit spectroscopic data; the degree and circumstances of the distinct kinematics vary from complete counterrotation of all of the gas from all of the stars (NGC 3626) to nuclear gas disks decoupled from the stars (NGC 5854) to anomalous velocity central gas components (NGC 3900 and NGC 4772). In the three objects mapped in H I, the neutral gas extends far beyond the optical radius, RH I/R25 ≥ 2. In general, the H I surface density is very low, and the outer H I is patchy and asymmetric (NGC 3900) or found in a distinct ring, exterior to the optical edge (NGC 3626 and NGC 4772). While the overall H I velocity fields are dominated by circular motions, strong warps are suggested in the outer regions by bending of the minor axis isovelocity contours (NGC 3900) and/or systematic shifts in position angle between inner and outer rings (NGC 3626 and NGC 4772). In the interior, coincidence is found between the Hα and H I in rings, sometimes partial and crisscrossed by dust lanes. Optical imaging is also presented for NGC 4138 previously reported by Jore et al. to show counterrotating stellar components. The multiwavelength evidence is interpreted in terms of the kinematic "memory" of past minor mergers in objects that otherwise exhibit no morphological signs of interaction.
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