CON-quest: II. Spatially and spectrally resolved HCN/HCO+ line ratios in local luminous and ultraluminous infrared galaxies
Journal article, 2024
Context. Nuclear regions of ultraluminous and luminous infrared galaxies (U/LIRGs) are powered by starbursts and/or active galactic nuclei (AGNs). These regions are often obscured by extremely high columns of gas and dust. Molecular lines in the submillimeter windows have the potential to determine the physical conditions of these compact obscured nuclei (CONs).
Aims. We aim to reveal the distributions of HCN and HCO+ emission in local U/LIRGs and investigate whether and how they are related to galaxy properties. Methods. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we have conducted sensitive observations of the HCN J = 3-2 and HCO+J = 3-2 lines toward 23 U/LIRGs in the local Universe (z < 0.07) with a spatial resolution of ~0.3″ ( ~50-400 pc).
Results. We detected both HCN and HCO+ in 21 galaxies, only HCN in one galaxy, and neither in one galaxy. The global HCN/HCO+ line ratios, averaged over scales of ~0.5-4 kpc, range from 0.4 to 2.3, with an unweighted mean of 1.1. These line ratios appear to have no systematic trend with bolometric AGN luminosity or star formation rate. The line ratio varies with position and velocity within each galaxy, with an average interquartile range of 0.38 on a spaxel-by-spaxel basis. In eight out of ten galaxies known to have outflows and/or inflows, we found spatially and kinematically symmetric structures of high line ratios. These structures appear as a collimated bicone in two galaxies and as a thin spherical shell in six galaxies.
Conclusions. Non-LTE analysis suggests that the high HCN/HCO+ line ratio in outflows is predominantly influenced by the abundance ratio. Chemical model calculations indicate that the enhancement of HCN abundance in outflows is likely due to high-temperature chemistry triggered by shock heating. These results imply that the HCN/HCO+ line ratio can aid in identifying the outflow geometry when the shock velocity of the outflows is sufficiently high to heat the gas.
Aims. We aim to reveal the distributions of HCN and HCO+ emission in local U/LIRGs and investigate whether and how they are related to galaxy properties. Methods. Using the Atacama Large Millimeter/submillimeter Array (ALMA), we have conducted sensitive observations of the HCN J = 3-2 and HCO+J = 3-2 lines toward 23 U/LIRGs in the local Universe (z < 0.07) with a spatial resolution of ~0.3″ ( ~50-400 pc).
Results. We detected both HCN and HCO+ in 21 galaxies, only HCN in one galaxy, and neither in one galaxy. The global HCN/HCO+ line ratios, averaged over scales of ~0.5-4 kpc, range from 0.4 to 2.3, with an unweighted mean of 1.1. These line ratios appear to have no systematic trend with bolometric AGN luminosity or star formation rate. The line ratio varies with position and velocity within each galaxy, with an average interquartile range of 0.38 on a spaxel-by-spaxel basis. In eight out of ten galaxies known to have outflows and/or inflows, we found spatially and kinematically symmetric structures of high line ratios. These structures appear as a collimated bicone in two galaxies and as a thin spherical shell in six galaxies.
Conclusions. Non-LTE analysis suggests that the high HCN/HCO+ line ratio in outflows is predominantly influenced by the abundance ratio. Chemical model calculations indicate that the enhancement of HCN abundance in outflows is likely due to high-temperature chemistry triggered by shock heating. These results imply that the HCN/HCO+ line ratio can aid in identifying the outflow geometry when the shock velocity of the outflows is sufficiently high to heat the gas.
ISM: molecules
Galaxies: ISM
Galaxies: nuclei
ISM: jets and outflows
Galaxies: evolution
Author
Y. Nishimura
University of Tokyo
National Astronomical Observatory of Japan
Susanne Aalto
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Mark Gorski
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Sabine König
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Kyoko Onishi
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Clare Wethers
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Chentao Yang
Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics
Loreto Barcos-Munoz
National Radio Astronomy Observatory
F. Combes
Paris Observatory
T. Diaz-Santos
European University Cyprus
Foundation for Research and Technology-Hellas (FORTH)
J. S. Gallagher III
University of Wisconsin Madison
Macalester College
S. G. Burillo
Spanish National Observatory (OAN)
E. Gonzalez-Alfonso
University of Alcalá
T. R. Greve
Technical University of Denmark (DTU)
Niels Bohr Institute
N. Harada
The Graduate University for Advanced Studies (SOKENDAI)
National Astronomical Observatory of Japan
C. Henkel
Max Planck Society
King Abdulaziz University
M. Imanishi
National Astronomical Observatory of Japan
K. Kohno
University of Tokyo
S. T. Linden
University of Arizona
J. G. Mangum
National Radio Astronomy Observatory
S. Martin
European Southern Observatory Santiago
Atacama Large Millimeter-submillimeter Array (ALMA)
Sebastien Muller
Chalmers, Space, Earth and Environment, Onsala Space Observatory
G. Privon
University of Virginia
National Radio Astronomy Observatory
College of Liberal Arts and Sciences
C. Ricci
Beijing University of Technology
Diego Portales University
F. Stanley
Institut de Radioastronomie Millimétrique (IRAM)
P. van der Werf
Leiden University
Serena Viti
Leiden University
University College London (UCL)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 686 A48Exploring the Hidden Dusty Nuclei of Galaxies (HIDDeN)
European Research Council (ERC) (789410), 2018-10-01 -- 2023-09-30.
Molecules as Diagnostic Tools for Active and Obscured Galaxies
Swedish Research Council (VR) (2011-4143), 2012-01-01 -- 2014-12-31.
Subject Categories
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
DOI
10.1051/0004-6361/202348331