Peering through the dust: Evidence for a supermassive black hole at the nucleus of Centaurus A from VLT infrared spectroscopy

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Title: Peering through the dust: Evidence for a supermassive black hole at the nucleus of Centaurus A from VLT infrared spectroscopy
Author: Marconi, Alessandro; Capetti, Alessandro; Axon, David; Koekemoer, Anton; Macchetto, Duccio; Schreier, Ethan
Abstract: 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. (Refer to PDF file for exact formulas).
Description: Also archived in: arXiv:astro-ph/0011059 v1 2 Nov 2000
Record URI: http://hdl.handle.net/1850/1758
Date: 2001-03-10

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