Disentangling the Circumnuclear Environs of Centaurus A. II. On the Nature of the Broad Absorption Line
Journal article, 2010

We report on atomic gas (H I) and molecular gas (as traced by CO(2-1)) redshifted absorption features toward the nuclear regions of the closest powerful radio galaxy, Centaurus A (NGC 5128). Our H I observations using the Very Long Baseline Array allow us to discern with unprecedented sub-parsec resolution H I absorption profiles toward different positions along the 21 cm continuum jet in the inner 0farcs3 (or 5.4 pc). In addition, our CO(2-1) data obtained with the Submillimeter Array probe the bulk of the absorbing molecular gas with little contamination by emission, which was not possible with previous CO single-dish observations. We shed light on the physical properties of the gas in the line of sight with these data, emphasizing the still open debate about the nature of the gas that produces the broad absorption line (~55 km s–1). First, the broad H I line is more prominent toward the central and brightest 21 cm continuum component than toward a region along the jet at a distance ~20 mas (or 0.4 pc) further from the nucleus. This indicates that the broad absorption line arises from gas located close to the nucleus, rather than from diffuse and more distant gas. Second, the different velocity components detected in the CO(2-1) absorption spectrum match well with other molecular lines, such as those of HCO+(1-0), except the broad absorption line that is detected in HCO+(1-0) (and most likely related to that of the H I). Dissociation of molecular hydrogen due to the active galactic nucleus seems to be efficient at distances r lsim 10 pc, which might contribute to the depth of the broad H I and molecular lines.


galaxies: ISM

galaxies: elliptical and lenticular

galaxies: structure

quasars: absorption lines

galaxies: individual (NGC 5128)


D. Espada

Academia Sinica

CSIC - Instituto de Astrofísica de Andalucía (IAA)

Harvard-Smithsonian Center for Astrophysics

A. B. Peck

Harvard-Smithsonian Center for Astrophysics

Atacama Large Millimeter-submillimeter Array (ALMA)

National Radio Astronomy Observatory Socorro

S. Matsushita

Atacama Large Millimeter-submillimeter Array (ALMA)

Academia Sinica

K. Sakamoto

Academia Sinica

C. Henkel

Max Planck Society

D. Iono

National Astronomical Observatory of Japan

F. P. Israel

Leiden University

Sebastien Muller

Chalmers, Earth and Space Sciences, Onsala Space Observatory

G. Petitpas

Harvard-Smithsonian Center for Astrophysics

Y. Pihlstrom

University of New Mexico

National Radio Astronomy Observatory Socorro

G. Taylor

University of New Mexico

National Radio Astronomy Observatory Socorro

D.-V. Trung

Vietnam Academy of Science and Technology

Academia Sinica

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 720 1 666-678

Subject Categories

Astronomy, Astrophysics and Cosmology


Basic sciences



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