Disentangling the Circumnuclear Environs of Centaurus A. III. An Inner Molecular Ring, Nuclear Shocks, and the CO to Warm H-2 Interface
Journal article, 2017
We present the distribution and kinematics of the molecular gas in the circumnuclear disk (CND; 400 pc ×200 pc) of Centaurus A with resolutions of ∼5 pc (0.″3) and shed light onto the mechanism feeding the active galactic nucleus (AGN) using CO(3-2), HCO + (4-3), HCN(4-3), and CO(6-5) observations obtained with ALMA. Multiple filaments or streamers of tens to a hundred parsec scale exist within the CND, which form a ring-like structure with an unprojected diameter of 9″ ×6″ (162 pc ×108 pc) and a position angle P.A. ≃ 155°. Inside the nuclear ring, there are two leading and straight filamentary structures with lengths of about 30-60 pc at P.A. ≃ 120° on opposite sides of the AGN, with a rotational symmetry of 180° and steeper position-velocity diagrams, which are interpreted as nuclear shocks due to non-circular motions. Along the filaments, and unlike other nearby AGNs, several dense molecular clumps present low HCN/HCO + (4-3) ratios (≲0.5). The filaments abruptly end in the probed transitions at r ≃ 20 pc from the AGN, but previous near-IR H 2 (J = 1-0)S(1) maps show that they continue in an even warmer gas phase (T ∼ 1000 K), winding up in the form of nuclear spirals, and forming an inner ring structure with another set of symmetric filaments along the N-S direction and within r ≃ 10 pc. The molecular gas is governed primarily by non-circular motions, being the successive shock fronts at different scales where loss of angular momentum occurs, a mechanism that may feed efficiently powerful radio galaxies down to parsec scales.
galaxies: structure
cD
ISM: molecules
galaxies: elliptical and lenticular
galaxies: individual (NGC 5128)
Author
D. Espada
National Institutes of Natural Sciences - National Astronomical Observatory of Japan
Atacama Large Millimeter-submillimeter Array
Sokendai Graduate University for Advanced Studies
S. Matsushita
Institute of Astrophysics and Astronomy, Academia Sinica Taiwan
R.E. Miura
National Institutes of Natural Sciences - National Astronomical Observatory of Japan
F.P. Israel
Leiden Observatory Research Institute
N. Neumayer
Max Planck Institut fur Astronomie
S. Martin
European Southern Observatory Santiago
Atacama Large Millimeter-submillimeter Array
C. Henkel
Max Planck Institut fur Radioastronomie
King Abdulaziz University
T. Izumi
University of Tokyo
D. Iono
National Institutes of Natural Sciences - National Astronomical Observatory of Japan
Sokendai Graduate University for Advanced Studies
Susanne Aalto
Astronomy and Plasmaphysics
J. Ott
National Radio Astronomy Observatory Socorro
A.B. Peck
Gemini Observatory
A.C. Quillen
University of Rochester
K. Kohno
University of Tokyo
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 843 2 136Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.3847/1538-4357/aa78a9