EXCITATION MECHANISMS FOR HCN(1-0) AND HCO+ (1-0) IN GALAXIES FROM THE GREAT OBSERVATORIES ALL-SKY LIRG SURVEY
Journal article, 2015
We present new Institut de Radioastronomie Millimetrique (TRAM) 30 m spectroscopic observations of the similar to 88 GHz band, including emission from the CCH (N = 1 -> 0) multiplet, HCN (J = 1 -> 0), HCO (J = 1 -> 0), and HNC (J = 1 -> 0), for a sample of 58 local luminous and ultraluminous infrared galaxies from the Great Observatories All-sky LIRG Survey (GOALS). By combining our new TRAM 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 (L'(HCN(1 0))/ L'(HCO+(1-o))) = 1.84), compared to composite and starburst-dominated systems (L'HCN(1413/(1-0)) = 1.14, and 0.88, respectively). However, some composite and starburst systems have LH/ CN (1 0) /LH/ CO (1 0) 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 logio(L'(HCN(1-0))) and log(10)(LIR), consistent with most previous findings. Lc N(1 0) /LIR, typically interpreted as the dense-gas depletion time, appears to have no systematic trend with LIR for our sample of luminous and ultraluminous infrared galaxies, and has significant scatter. The galaxyintegrated L'(HCN(1-0)) and L'(HCO+(1-0)) 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.
galaxies: ISM
galaxies: active
galaxies: starburst
Author
G. Privon
University of Virginia
California Institute of Technology (Caltech)
University of Concepcion
R. Herrero-Illana
Spanish National Research Council (CSIC)
A. S. Evans
National Radio Astronomy Observatory
University of Virginia
K. Iwasawa
University of Barcelona
Miguel Angel Perez-Torres
Spanish National Research Council (CSIC)
L. Armus
Spitzer Science Center
T. Diaz-Santos
Spitzer Science Center
Diego Portales University
E. J. Murphy
California Institute of Technology (Caltech)
S. Stierwalt
University of Virginia
Susanne Aalto
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
J. Mazzarella
California Institute of Technology (Caltech)
Loreto Barcos-Munoz
University of Virginia
H. J. Borish
University of Virginia
H. Inami
National Optical Astronomy Observatory
D. C. Kim
National Radio Astronomy Observatory
E. Treister
University of Concepcion
J. A. Surace
Spitzer Science Center
S. Lord
SETI Institute
John Conway
Chalmers, Earth and Space Sciences, Onsala Space Observatory
D. Frayer
National Radio Astronomy Observatory
Antxon Alberdi
Spanish National Research Council (CSIC)
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 814 1 39Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
DOI
10.1088/0004-637X/814/1/39