CON-quest
Astronomy and Astrophysics, vol. 649, pp. A105
Abstract
Context. Some luminous and ultraluminous infrared galaxies (LIRGs and ULIRGs) host extremely compact (r < 100 pc) and dusty nuclei. The high extinction associated with large column densities of gas and dust toward these objects render them hard to detect at many wavelengths. The intense infrared radiation arising from warm dust in these sources can provide a significant fraction of the bolometric luminosity of the galaxy and is prone to excite vibrational levels of molecules such as HCN. This results in emission from the rotational transitions of vibrationally excited HCN (HCN-vib); the brightest emission is found in compact obscured nuclei (CONs; ΣHCN − vib > 1 L⊙ pc−2 in the J = 3−2 transition). However, there have been no systematic searches for CONs, and it is unknown how common they are. Aims. We aim to establish how common CONs are in the local Universe (z < 0.08), and whether their prevalence depends on the luminosity or other properties of the host galaxy. Methods. We conducted an Atacama Large Millimeter/submillimeter Array survey of the rotational J = 3−2 transition of HCN-vib in a volume-limited sample of 46 far-infrared luminous galaxies. Results. Compact obscured nuclei are identified in 38−13+18% of the ULIRGs, 21−6+12% of the LIRGs, and 0−0+9% of the lower luminosity galaxies. We find no dependence on the inclination of the host galaxy, but strong evidence of lower IRAS 25 μm to 60 μm flux density ratios (f25/f60) in CONs (with the exception of one galaxy, NGC 4418) compared to the rest of the sample. Furthermore, we find that CONs have stronger silicate features (s9.7 μm), but similar polycyclic aromatic hydrocarbon equivalent widths (EQW6.2 μm) compared to other galaxies. Along with signatures of molecular inflows seen in the far-infrared in most CONs, submillimeter observations also reveal compact, often collimated, outflows. Conclusions. In the local Universe, CONs are primarily found in (U)LIRGs, in which they are remarkably common. As such systems are often highly disturbed, inclinations are difficult to estimate, and high-resolution continuum observations of the individual nuclei are required to determine if the CON phenomenon is related to the inclinations of the nuclear disks. Further studies of the in- and outflow properties of CONs should also be conducted to investigate how these are connected to each other and to the CON phenomenon. The lower f25/f60 ratios in CONs as well as the results for the mid-infrared diagnostics investigated (EQW6.2 μm and s9.7 μm) are consistent with the notion that large dust columns gradually shift the radiation from the hot nucleus to longer wavelengths, making the mid- and far-infrared “photospheres” significantly cooler than the interior regions. Finally, to assess the importance of CONs in the context of galaxy evolution, it is necessary to extend this study to higher redshifts where (U)LIRGs are more common.
Authors 31
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Chalmers University of Technology
Affiliation as printed
Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
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Chalmers University of Technology
Affiliation as printed
Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
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Chalmers University of Technology
Affiliation as printed
Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
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Chalmers University of Technology
Affiliation as printed
Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
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Chalmers University of Technology
Affiliation as printed
Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
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Chalmers University of Technology
Affiliation as printed
Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
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Chalmers University of Technology
Affiliation as printed
Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
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Chalmers University of Technology
Affiliation as printed
Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
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Centre National de la Recherche Scientifique · Collège de France · Université Paris Sciences et Lettres · Observatoire de Paris · Sorbonne Université · Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères
Affiliation as printed
Observatoire de Paris, LERMA, College de France, CNRS, PSL Univ., Sorbonne University, UPMC, Paris, France
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Affiliation as printed
Universidad de Alcalá, Departamento de Física y Matemáticas, Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain
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National Radio Astronomy Observatory
Affiliation as printed
National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
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National Radio Astronomy Observatory · University of Virginia
Affiliation as printed
Department of Astronomy, 530 McCormick Road, University of Virginia, Charlottesville, VA 22904, USA
National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
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National Radio Astronomy Observatory
Affiliation as printed
National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
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National Radio Astronomy Observatory
Affiliation as printed
National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
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Affiliation as printed
Department of Astronomy, 530 McCormick Road, University of Virginia, Charlottesville, VA 22904, USA
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Chinese Academy of Sciences · FORTH Institute of Astrophysics · National Astronomical Observatories · Foundation for Research and Technology Hellas · Universidad Diego Portales
Affiliation as printed
Chinese Academy of Sciences South America Center for Astronomy (CASSACA), National Astronomical Observatories, CAS, Beijing 100101, PR China
Institute of Astrophysics, Foundation for Research and Technology–Hellas (FORTH), Heraklion 70013, Greece
Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
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Atacama Large Millimeter Submillimeter Array · European Southern Observatory
Affiliation as printed
European Southern Observatory, Alonso de Córdova 3107, Vitacura, 763 0355 Santiago, Chile
Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, 763 0355 Santiago, Chile
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Institute of Astronomy and Astrophysics, Academia Sinica · Academia Sinica
Affiliation as printed
Institute of Astronomy and Astrophysics, Academia Sinica, 11F of AS/NTU Astronomy-Mathematics Building, No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan ROC
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Institute of Astronomy and Astrophysics, Academia Sinica · National Institutes of Natural Sciences · National Astronomical Observatory of Japan · Academia Sinica
Affiliation as printed
Institute of Astronomy and Astrophysics, Academia Sinica, 11F of AS/NTU Astronomy-Mathematics Building, No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan ROC
National Astronomical Observatory of Japan, National Institutes of Natural Sciences (NINS), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
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University of Manchester · Instituto de Astrofísica de Andalucía
Affiliation as printed
Instituto de Astrofísica de Andalucia (CSIC), Glorieta de al Astronomia s/n, 18008 Granada, Spain
Jodrell Bank Centre for Astrophysics, Department of Physics & Astronomy, School of Natural Sciences, The University of Manchester, Manchester M13 9PL, UK
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University of Wisconsin–Madison
Affiliation as printed
Department of Astronomy, University of Wisconsin-Madison, 5534 Sterling, 475 North Charter Street, Madison, WI 53706, USA
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Leiden University · Leiden Observatory
Affiliation as printed
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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Leiden University · Leiden Observatory · University College London
Affiliation as printed
Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
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DTU Space · University College London · Technical University of Denmark
Affiliation as printed
Cosmic Dawn Center (DAWN), DTU-Space, Technical University of Denmark, Elektrovej 327, 2800 Kgs. Lyngby, Denmark
Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
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Affiliation as printed
Observatorio de Madrid, OAN-IGN, Alfonso XII, 3, 28014 Madrid, Spain
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King Abdulaziz University · Max Planck Institute for Radio Astronomy
Affiliation as printed
Astron. Dept., King Abdulaziz University, PO Box 80203, 21589 Jeddah, Saudi Arabia
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
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National Institutes of Natural Sciences · National Astronomical Observatory of Japan
Affiliation as printed
National Astronomical Observatory of Japan, National Institutes of Natural Sciences (NINS), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
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National Institutes of Natural Sciences · National Astronomical Observatory of Japan
Affiliation as printed
National Astronomical Observatory of Japan, National Institutes of Natural Sciences (NINS), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
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National Institutes of Natural Sciences · National Astronomical Observatory of Japan · The University of Tokyo
Affiliation as printed
Institute of Astronomy, The University of Tokyo, 2-21-1, Osawa, Mitaka, Tokyo 181-0015, Japan
National Astronomical Observatory of Japan, National Institutes of Natural Sciences (NINS), 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
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George Mason University · Peking University · Universidad Diego Portales
Affiliation as printed
George Mason University, Department of Physics & Astronomy, MS 3F3, 4400 University Drive, Fairfax, VA 22030, USA
Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, PR China
Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
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Affiliation as printed
Argelander Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
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