1 research outputs found
Peering through the dust: Evidence for a supermassive Black Hole at the nucleus of Centaurus A from VLT IR spectroscopy
We used the near infrared spectrometer ISAAC at the ESO 'Very Large
Telescope' to map the velocity field of Centaurus A (NGC 5128) at several
position angles and locations in the central 20" of the galaxy. The high
spatial resolution (~0.5") velocity fields from both ionized and molecular gas
(PaBeta, [FeII], BrGamma, and H2) are not compromised by either excitation
effects or obscuration. We identify three distinct kinematical systems: (i) a
rotating 'nuclear disk' of ionized gas, confined to the inner 2", the
counterpart of the PaAlpha feature previously revealed by HST/NICMOS imaging;
(ii) a ring-like system with a ~6" inner radius detected only in H2, likely the
counterpart of the 100pc-scale structure detected in CO by other authors; (iii)
a normal extended component of gas rotating in the galactic potential. The
nuclear disk is in keplerian rotation around a central mass concentration, dark
(M/L>20 Msun/LsunK) and point-like at the spatial resolution of the data
(R<0.25" ~4pc). We interpret this mass concentration as a supermassive black
hole. Its dynamical mass based on the line velocities and disk inclination
(i>15deg) is M=2(+3.0;-1.4) 10^8 Msun. The ring-like system is probably
characterized by non-circular motions; a 'figure-of-8' pattern observed in the
H2 position-velocity diagram might provide kinematical evidence for the
presence of a nuclear bar.Comment: 43 pages, 19 figures, Astrophysical Journal in press, higher quality
figures available at http://www.arcetri.astro.it/~marconi/pubs.htm