Hidden or missing outflows in highly obscured galaxy nuclei?
Journal article, 2019
Understanding the nuclear growth and feedback processes in galaxies requires investigating their often obscured central regions. One way to do this is to use (sub)millimeter line emission from vibrationally excited HCN (HCN-vib), which is thought to trace warm and highly enshrouded galaxy nuclei. It has been suggested that the most intense HCN-vib emission from a galaxy is connected to a phase of nuclear growth that occurs before the nuclear feedback processes have been fully developed. Aims. We aim to investigate if there is a connection between the presence of strong HCN-vib emission and the development of feedback in (ultra)luminous infrared galaxies ((U)LIRGs). Methods. We collected literature and archival data to compare the luminosities of rotational lines of HCN-vib, normalized to the total infrared luminosity, to the median velocities of 119 μm OH absorption lines, potentially indicating outflows, in a total of 17 (U)LIRGs. Results. The most HCN-vib luminous systems all lack signatures of significant molecular outflows in the far-infrared OH absorption lines. However, at least some of the systems with bright HCN-vib emission have fast and collimated outflows that can be seen in spectral lines at longer wavelengths, including in millimeter emission lines of CO and HCN (in its vibrational ground state) and in radio absorption lines of OH. Conclusions. We conclude that the galaxy nuclei with the highest L HCN-vib /L IR do not drive wide-angle outflows that are detectable using the median velocities of far-infrared OH absorption lines. This is possibly because of an orientation effect in which sources oriented in such a way that their outflows are not along our line of sight also radiate a smaller proportion of their infrared luminosity in our direction. It could also be that massive wide-angle outflows destroy the deeply embedded regions responsible for bright HCN-vib emission, so that the two phenomena cannot coexist. This would strengthen the idea that vibrationally excited HCN traces a heavily obscured stage of evolution before nuclear feedback mechanisms are fully developed.
Galaxies: ISM
Galaxies: evolution
ISM: jets and outflows
ISM: molecules
Galaxies: nuclei
Author
Niklas Falstad
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
F. Hallqvist
Chalmers, Space, Earth and Environment
Susanne Aalto
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Sabine König
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Sebastien Muller
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Rebeca Aladro
Max Planck Society
F. Combes
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
A. S. Evans
University of Virginia
National Radio Astronomy Observatory
G. A. Fuller
University of Manchester
J. S. Gallagher III
University of Wisconsin Madison
S. G. Burillo
Spanish National Observatory (OAN)
E. Gonzalez-Alfonso
University of Alcalá
T. R. Greve
Technical University of Denmark (DTU)
University College London (UCL)
C. Henkel
Max Planck Society
King Abdulaziz University
M. Imanishi
National Astronomical Observatory of Japan
T. Izumi
National Astronomical Observatory of Japan
J. G. Mangum
National Radio Astronomy Observatory
S. Martin
European Southern Observatory Santiago
Atacama Large Millimeter-submillimeter Array (ALMA)
G. Privon
University of Florida
K. Sakamoto
Academia Sinica
S. Veilleux
University of Maryland
P. van der Werf
Leiden University
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 623 A29Subject Categories
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
Environmental Sciences
DOI
10.1051/0004-6361/201834586