101. VLT diffraction-limited imaging and spectroscopy in the NIR: Weighing the black hole in Centaurus A with NACO
- Author
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H. W. Rix, Klaus Meisenheimer, Rainer Lenzen, M. A. Prieto, Markus Hartung, N. Haering-Neumayer, and Michele Cappellari
- Subjects
Diffraction ,Physics ,Stellar mass ,Centaurus A ,Astrophysics (astro-ph) ,Velocity dispersion ,FOS: Physical sciences ,Astronomy and Astrophysics ,Astrophysics ,Astrophysics::Cosmology and Extragalactic Astrophysics ,01 natural sciences ,Spectral line ,law.invention ,Black hole ,Space and Planetary Science ,law ,0103 physical sciences ,Astrophysics::Earth and Planetary Astrophysics ,Hydrostatic equilibrium ,010306 general physics ,Spectroscopy ,010303 astronomy & astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
We present high spatial resolution near-infrared spectra and images of the nucleus of Centaurus A (NGC 5128) obtained with NAOS-CONICA at the VLT. The adaptive optics corrected data have a spatial resolution of 0.06" (FWHM) in K- and 0.11" in H-band, four times higher than previous studies. The observed gas motions suggest a kinematically hot disk which is orbiting a central object and is oriented nearly perpendicular to the nuclear jet. We model the central rotation and velocity dispersion curves of the [FeII] gas orbiting in the combined potential of the stellar mass and the (dominant) black hole. Our physically most plausible model, a dynamically hot and geometrically thin gas disk, yields a black hole mass of M_bh = (6.1 +0.6/-0.8) 10^7 M_sun. As the physical state of the gas is not well understood, we also consider two limiting cases: first a cold disk model, which completely neglects the velocity dispersion; it yields an M_bh estimate that is almost two times lower. The other extreme case is to model a spherical gas distribution in hydrostatic equilibrium through Jeans equation. Compared to the hot disk model the best-fit black hole mass increases by a factor of 1.5. This wide mass range spanned by the limiting cases shows how important the gas physics is even for high resolution data. Our overall best-fitting black hole mass is a factor of 2-4 lower than previous measurements. With our revised M_bh estimate, Cen A's offset from the M_bh-sigma relation is significantly reduced; it falls above this relation by a factor of ~2, which is close to the intrinsic scatter of this relation. (Abridged), Comment: 12 pages, 14 figures, including minor changes following the referee report; accepted for publication in The Astrophysical Journal
- Published
- 2016