Dynamics of the large-scale disc in NGC 1068

Summary

Observations

While NGC 1068 has received much attention in recent years, little is known of the large-scale dynamics of the ionized gas in this nearby Seyfert galaxy. We have used the Hawaii Imaging Fabry-Perot Interferometer (HIFI, Bland & Tully 1989) at the CFHT to obtain detailed spectrophotometry at 65 km s⁻¹ FWHM resolution for Hα and the [NII]λλ6548, 6583 lines. The final maps are derived from ∼ 100 000 fits to spectra taken at 0.4″ increments over a 200″ field-of-view. The flux-weighted Hα + [NII] velocity field is presented in Figure 1.

Deep images of NGC 1068 reveal an outer θ-shaped ring lying roughly east-west which encompasses a visibly bright, inner disc with diameter ∼ 20 kpc (230″), orthogonal to the outer ring. The Hα line flux is dominated by a luminous, elliptic ring of HII regions with diameter 3 kpc and major axis 45^°. The “3 kpc ring” is aligned with an oval, bar-like distortion recently discovered at λ2µ (Scoville et al. 1988). The inner disc is marked by high concentrations of atomic and molecular gas (∼ 10¹⁰M_⊙) which is thought to fuel the rapid star formation that characterizes the 3 kpc ring (Scoville et al. 1983). Most of the ring bolometric luminosity (1.5 × 10¹¹L_°), which is comparable to that of the active nucleus, emerges in the far-infrared as re-radiation from dust heated by young stars (Telesco et al. 1984).

From Figure 1, the large-scale disc appears to undergo flat rotation with V(R_max) = 170/ sin i where R_max ≈ 30″.