The supermassive black hole and double nucleus of the core elliptical NGC 5419

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 (approximate to 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 (approximate to 70 pc). Outside of the central double nucleus, we measure an almost constant velocity dispersion of sigma similar to 350 km s(-1). In the region where the double nucleus is located, the dispersion rises steeply to a peak value of similar to 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 similar to 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(-1.9)(+2.7) x 10(9) M-circle dot. 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 approximate to 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 MBH related to the secondary nucleus are small.

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