NGC 4102: HIGH-RESOLUTION INFRARED OBSERVATIONS OF A NUCLEAR STARBURST RING

The composite galaxy NGC 4102 hosts a LINER nucleus and a starburst. We mapped NGC 4102 in the 12.8 μm line of [Ne ii], using the echelon spectrometer TEXES on the NASA IRTF, to obtain a data cube with 1.″5 spatial, and 25 km s−1 spectral, resolution. Combining near-infrared, radio, and the [Ne ii] data shows that the extinction to the starburst is substantial, more than 2 mag at the K band, and that the neon abundance is less than half solar. We find that the star formation in the nuclear region is confined to a rotating ring or disk of 4.″3 (∼300 pc) diameter, inside the inner Lindblad resonance. This region is an intense concentration of mass, with a dynamical mass ∼3 × 109 M☉, and of star formation. The young stars in the ring produce the [Ne ii] flux reported by Spitzer for the entire galaxy. The mysterious blue component of line emission detected in the near-infrared is also seen in [Ne ii]; it is not a normal active galactic nucleus outflow.