2016MNRAS.462.2847M

We obtained adaptive-optics assisted SINFONI observations of the central regions of the giant elliptical galaxy NGC 5419 with a spatial resolution of 0.2 arcsec (≃55 pc). NGC 5419 has a large depleted stellar core with a radius of 1.58 arcsec (430 pc). HST and SINFONI images show a point source located at the galaxy's photocentre, which is likely associated with the low-luminosity AGN previously detected in NGC 5419. Both the HST and SINFONI images also show a second nucleus, off-centred by 0.25 arcsec (≃70 pc). Outside of the central double nucleus, we measure an almost constant velocity dispersion of σ ∼ 350 km s^–1. In the region where the double nucleus is located, the dispersion rises steeply to a peak value of ∼420 km s^–1. In addition to the SINFONI data, we also obtained stellar kinematics at larger radii from the South African Large Telescope. While NGC 5419 shows low rotation (v < 50 km s^–1), the central regions (inside ∼4 r_b) clearly rotate in the opposite direction to the galaxy's outer parts. We use orbit-based dynamical models to measure the black hole mass of NGC 5419 from the kinematical data outside of the double nuclear structure. The models imply M_BH=7.2^{+2.7}_{-1.9} x10⁹ M_☉. The enhanced velocity dispersion in the region of the double nucleus suggests that NGC 5419 possibly hosts two supermassive black holes at its centre, separated by only ≃70 pc. Yet our measured M_BH is consistent with the black hole mass expected from the size of the galaxy's depleted stellar core. This suggests, that systematic uncertainties in M_BH related to the secondary nucleus are small.