The nature of the molecular gas system in the core of NGC 1275

We present near-infrared integral field spectroscopy of the central kiloparsec of NGC 1275 at the heart of the Perseus cluster of galaxies, obtained with the Integral Field Unit (IFU) of the United Kingdom Infrared Telescope (UKIRT) Imaging Spectrometer (UIST). The nuclear rovibrational H 2 emission is spatially resolved and is likely to originate approximately 50 pc from the active nucleus. The Paα emission is, by contrast, spatially unresolved. The requirements for thermal excitation of the H 2 by nuclear X-radiation, its kinematics on subarcsec scales and its stability against self-gravity together suggest that the observed H 2 is part of a clumpy disc rotating about the radio-jet axis. The sharp jump in the H 2 velocity across the nucleus implies a black hole mass of 3.4 x 10 8 M ○. , with a systematic error of ±0.18 dex due to the uncertainty in the radio-jet inclination. This agrees well with the value implied by the empirical correlation between black hole mass and stellar velocity dispersion for nearby elliptical galaxies, and is ∼100 times the stellar mass in this region.