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 ( \approx 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 ( \approx 70 pc ) .
Outside of the central double nucleus , we measure an almost constant velocity dispersion of \sigma \sim 350 km s ^ { -1 } .
In the region where the double nucleus is located , the dispersion rises steeply to a peak value of \sim 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 \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 NGC 5419 from the kinematical data outside of the double nuclear structure .
The models imply M _ { \mathrm { BH } } = 7.2 ^ { +2.7 } _ { -1.9 } \times 10 ^ { 9 } M _ { \sun } .
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 \approx 70 pc .
Yet our measured M _ { \mathrm { 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 _ { \mathrm { BH } } related to the secondary nucleus are small .