Excitation Mechanisms for Hcn(1–0) and Hco+(1–0) in Galaxies From the Great Observatories All-sky Lirg Survey*
Year: 2015
Type: article
Abstract: ABSTRACT We present new Institut de Radioastronomie Millimétrique (IRAM) 30 m spectroscopic observations of the ∼88 GHz band, including emission from the multiplet, HCN ( , , and , for a sample of 58 local luminous and ultraluminous infrared galaxies from the Great Observatories All-sky LIRG Survey (GOALS). By combining our new IRAM data with literature data and Spitzer/IRS spectroscopy, we study the correspondence between these putative tracers of dense gas and the relative contribution of active galactic nuclei (AGNs) and star formation to the mid-infrared luminosity of each system. We find the HCN (1–0) emission to be enhanced in AGN-dominated systems ( / ), compared to composite and starburst-dominated systems ( / and 0.88, respectively). However, some composite and starburst systems have / ratios comparable to those of AGNs, indicating that enhanced HCN emission is not uniquely associated with energetically dominant AGNs. After removing AGN-dominated systems from the sample, we find a linear relationship (within the uncertainties) between log10( ) and log10(L IR), consistent with most previous findings. /L IR, typically interpreted as the dense-gas depletion time, appears to have no systematic trend with L IR for our sample of luminous and ultraluminous infrared galaxies, and has significant scatter. The galaxy-integrated and emission do not appear to have a simple interpretation in terms of the AGN dominance or the star formation rate, and are likely determined by multiple processes, including density and radiative effects.
Source: The Astrophysical Journal
Institutions: California Institute of Technology, University of Concepción, Infrared Processing and Analysis Center, University of Virginia, Instituto de Astrofísica de Andalucía, National Radio Astronomy Observatory, Institució Catalana de Recerca i Estudis Avançats, Institut de Ciències del Cosmos, Universitat de Barcelona, Universidad Diego Portales, Chalmers University of Technology, Search for Extraterrestrial Intelligence
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: bronze
Funders: National Science Foundation, National Aeronautics and Space Administration, California Institute of Technology, Aspen Center for Physics, Space Telescope Science Institute, National Socio-Environmental Synthesis Center, Max-Planck-Gesellschaft, Centre National de la Recherche Scientifique, Jet Propulsion Laboratory, Comisión Nacional de Investigación Científica y Tecnológica, Institut de Ciències del Cosmos
Awards: G2309114461, The ISM of Luminous Infrared Galaxies: Tracing Gas Properties, Dynamics and Starburst/AGN Activity, G433322167, G4357913612, Programs on Critical Problems in Physics, Astrophysics and Biophysics at the Aspen Center for Physics, G58316358, G6273510985, G7075080176, G7983806569, G8240985459, G8896167186
OpenAlex ID: W2182785271