The hidden heart of the luminous infrared galaxy IC 860: I. A molecular inflow feeding opaque, extreme nuclear activity
Journal article, 2019
High-resolution (0.'03-0.'09 (9-26 pc)) ALMA (100-350 GHz (λ3 to 0.8 mm)) and (0.'04 (11 pc)) VLA 45 GHz measurements have been used to image continuum and spectral line emission from the inner (100 pc) region of the nearby infrared luminous galaxy IC 860. We detect compact (r ∼ 10 pc), luminous, 3 to 0.8 mm continuum emission in the core of IC 860, with brightness temperatures TB > 160 K. The 45 GHz continuum is equally compact but significantly fainter in flux. We suggest that the 3 to 0.8 mm continuum emerges from hot dust with radius r ∼ 8 pc and temperature Td ∼ 280 K, and that it is opaque at millimetre wavelengths, implying a very large H2 column density N(H2)≥ 1026 cm-2. Vibrationally excited lines of HCN v2 = 1f J = 4 - 3 and 3-2 (HCN-VIB) are seen in emission and spatially resolved on scales of 40-50 pc. The line-to-continuum ratio drops towards the inner r = 4 pc, resulting in a ring-like morphology. This may be due to high opacities and matching HCN-VIB excitation- and continuum temperatures. The HCN-VIB emission reveals a north-south nuclear velocity gradient with projected rotation velocities of v = 100 km s-1 at r = 10 pc. The brightest emission is oriented perpendicular to the velocity gradient, with a peak HCN-VIB 3-2 TB of 115 K (above the continuum). Vibrational ground-state lines of HCN 3-2 and 4-3, HC15N 4-3, HCO+ 3-2 and 4-3, and CS 7-6 show complex line absorption and emission features towards the dusty nucleus. Redshifted, reversed P-Cygni profiles are seen for HCN and HCO+ consistent with gas inflow with vin ≤ 50 km s-1. Foreground absorption structures outline the flow, and can be traced from the north-east into the nucleus. In contrast, CS 7-6 has blueshifted line profiles with line wings extending out to -180 km s-1. We suggest that a dense and slow outflow is hidden behind a foreground layer of obscuring, inflowing gas. The centre of IC 860 is in a phase of rapid evolution where an inflow is building up a massive nuclear column density of gas and dust that feeds star formation and/or AGN activity. The slow, dense outflow may be signaling the onset of feedback. The inner, r = 10 pc, IR luminosity may be powered by an AGN or a compact starburst, which then would likely require a top-heavy initial mass function.
ISM: molecules
Galaxies: active
Galaxies: evolution
Galaxies: ISM
ISM: jets and outflows
Galaxies: individual: IC 860
Author
Susanne Aalto
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Sebastien Muller
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Sabine König
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Niklas Falstad
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
J. G. Mangum
National Radio Astronomy Observatory
K. Sakamoto
Academia Sinica
G. Privon
University of Florida
J. S. Gallagher III
University of Wisconsin Madison
F. Combes
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
S. G. Burillo
Spanish National Observatory (OAN)
S. Martin
European Southern Observatory Santiago
Serena Viti
University College London (UCL)
P. van der Werf
Leiden University
A. S. Evans
National Radio Astronomy Observatory
University of Virginia
John H Black
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Eskil Varenius
University of Manchester
R. J. Beswick
University of Manchester
G. A. Fuller
University of Manchester
C. Henkel
King Abdulaziz University
Max Planck Society
K. Kohno
University of Tokyo
K. Alatalo
Space Telescope Science Institute (STScI)
S. Muhle
Argelander-Institut für Astronomie
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 627 A147Subject Categories
Energy Engineering
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
DOI
10.1051/0004-6361/201935480