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: evolution

galaxies: nuclei

galaxies: active



Susanne Aalto

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

S. Martin

Institut de RadioAstronomie Millimetrique (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 Millimetrique (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

National Radio Astronomy Observatory

University of Virginia

E. Sturm

Max Planck Society

J. Cernicharo

CSIC - Instituto de Ciencia de Materiales de Madrid (ICMM)

C. Henkel

King Abdulaziz University

Max Planck Society

T. R. Greve

University College London (UCL)

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 584 A42

Molecules as Diagnostic Tools for Active and Obscured Galaxies

Swedish Research Council (VR), 2012-01-01 -- 2014-12-31.

Subject Categories

Astronomy, Astrophysics and Cosmology


Onsala Space Observatory



More information

Latest update

9/6/2018 1