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


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 A147

Subject Categories

Energy Engineering

Astronomy, Astrophysics and Cosmology

Atom and Molecular Physics and Optics



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