NGC 4102: High-resolution Infrared Observations of a Nuclear Starburst Ring

Abstract

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 1farcs5 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 4farcs3 (~300 pc) diameter, inside the inner Lindblad resonance. This region is an intense concentration of mass, with a dynamical mass ~3 × 10⁹ M _sun, 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.