Probing highly obscured, self-absorbed galaxy nuclei with vibrationally excited HCN
Journal article, 2015
We present high resolution (0.'' 4) IRAM PdBI and ALMA mm and submm observations of the (ultra) luminous infrared galaxies ((U)LIRGs) IRAS 17208-0014, Arp220, IC 860 and Zw049.057 that reveal intense line emission from vibrationally excited (nu(2) = 1) J = 3-2 and 4-3 HCN. The emission is emerging from buried, compact (r < 17-70 pc) nuclei that have very high implied mid-infrared surface brightness >5 x 10(13) L-circle dot kpc(-2). These nuclei are likely powered by accreting supermassive black holes (SMBHs) and/or hot (>200 K) extreme starbursts. Vibrational, nu(2) = 1, lines of HCN are excited by intense 14 mu m mid-infrared emission and are excellent probes of the dynamics, masses, and physical conditions of (U)LIRG nuclei when H-2 column densities exceed 10(24) cm(-2). It is clear that these lines open up a new interesting avenue to gain access to the most obscured AGNs and starbursts. Vibrationally excited HCN acts as a proxy for the absorbed mid-infrared emission from the embedded nuclei, which allows for reconstruction of the intrinsic, hotter dust SED. In contrast, we show strong evidence that the ground vibrational state (. = 0), J = 3-2 and 4-3 rotational lines of HCN and HCO+ fail to probe the highly enshrouded, compact nuclear regions owing to strong self-and continuum absorption. The HCN and HCO+ line profiles are double-peaked because of the absorption and show evidence of non-circular motions-possibly in the form of in-or outflows. Detections of vibrationally excited HCN in external galaxies are so far limited to ULIRGs and early-type spiral LIRGs, and we discuss possible causes for this. We tentatively suggest that the peak of vibrationally excited HCN emission is connected to a rapid stage of nuclear growth, before the phase of strong feedback.
galaxies: active
galaxies: evolution
galaxies
galaxies: nuclei
Author
Susanne Aalto
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
S. Martin
Institut de Radioastronomie Millimétrique (IRAM)
Francesco Costagliola
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
E. Gonzalez-Alfonso
University of Alcalá
Sebastien Muller
Chalmers, Earth and Space Sciences, Onsala Space Observatory
K. Sakamoto
Academia Sinica
G. A. Fuller
University of Manchester
S. G. Burillo
Spanish National Observatory (OAN)
P. van der Werf
Leiden University
R. Neri
Institut de Radioastronomie Millimétrique (IRAM)
M. Spaans
University of Groningen
F. Combes
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
S. Viti
University College London (UCL)
S. Muhle
Argelander-Institut für Astronomie
L. Armus
California Institute of Technology (Caltech)
A. Evans
University of Virginia
National Radio Astronomy Observatory
E. Sturm
Max Planck Society
J. Cernicharo
Spanish National Research Council (CSIC)
C. Henkel
Max Planck Society
King Abdulaziz University
T. R. Greve
University College London (UCL)
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 584 A42Molecules as Diagnostic Tools for Active and Obscured Galaxies
Swedish Research Council (VR) (2011-4143), 2012-01-01 -- 2014-12-31.
Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Infrastructure
Onsala Space Observatory
DOI
10.1051/0004-6361/201526410