Circumnuclear Structures in the Interacting Seyfert Galaxy NGC 1241: Kinematics and Optical/Infrared Morphology

Abstract

We studied the spiral pattern in the inner 65 (1'' = 257 pc) central regions of the interacting active nucleus galaxy NGC 1241 using Gemini North Telescope high-resolution Ks- and J-band images and Hubble Space Telescope (HST) Paα and H- and (V + R)-band images with high resolution in the range from ~01 to ~03 along with intermediate to large-scale spectroscopy using the Multifunction Spectrograph at the Cordoba Observatory in Argentina. Our analysis of Paα emission images revealed a faint two-armed leading spiral pattern ending in the 56 × 34 clumpy ring discovered by Boker and coworkers, harboring a 16 long barlike structure almost perpendicular to the large-scale bar of NGC 1241. When we applied two-dimensional Fourier analysis at circumnuclear scales, we found that a two-arm trailing mode was dominant in Ks- and J-band images while the (V + R)-band images showed more complex structural features with a strong one-armed trailing mode. One-dimensional Fourier analysis showed a corotation (CR) located outward from the edge of the Paα bar. Our kinematics data gave an angular speed ΩCN of 350 ± 50 km s-1 kpc-1 for the trailing mode pattern. The rotation curve showed that the circumnuclear ring is located just inside the large-scale pattern inner Lindblad resonance (ILR), which has a radius of about r ~ 1 kpc. We also found, within the uncertainties present in such measurements, that the outer Lindblad resonance (OLR) of the circumnuclear pattern is coincident with the large-scale pattern ILR, indicating a possible connection between circumnuclear and global dynamics. Nevertheless, the estimated high molecular gas fraction (≥13%) and the inner pattern high angular speed at the central region of NGC 1241 point to a nuclear bar formation via self-gravitational instability.