The supermassive black hole and double nucleus of the core elliptical
  NGC5419
  We obtained adaptive-optics assisted SINFONI observations of the central
regions of the giant elliptical galaxy NGC5419 with a spatial resolution of 0.2
arcsec ($\approx 55$ pc). NGC5419 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 NGC5419. Both the HST and SINFONI
images also show a second nucleus, off-centred by 0.25 arcsec ($\approx 70$
pc). Outside of the central double nucleus, we measure an almost constant
velocity dispersion of $\sigma \sim 350$ km/s. In the region where the double
nucleus is located, the dispersion rises steeply to a peak value of $\sim 420$
km/s. In addition to the SINFONI data, we also obtained stellar kinematics at
larger radii from the South African Large Telescope. While NGC5419 shows low
rotation ($v < 50$ km/s), the central regions (inside $\sim 4 \, r_b$) 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 NGC5419 from the
kinematical data outside of the double nuclear structure. The models imply
M$_{\rm BH}=7.2^{+2.7}_{-1.9} \times 10^9$ M$_{\odot}$. The enhanced velocity
dispersion in the region of the double nucleus suggests that NGC5419 possibly
hosts two supermassive black holes at its centre, separated by only $\approx
70$ pc. Yet our measured M$_{\rm BH}$ 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$_{\rm BH}$ related to the secondary nucleus
are small.
