Subarcsecond imaging of the water emission in Arp 220
Journal article, 2017

Aims. Extragalactic observations of water emission can provide valuable insight into the excitation of the interstellar medium. In particular they allow us to investigate the excitation mechanisms in obscured nuclei, that is, whether an active galactic nucleus or a starburst dominates. Methods. We use subarcsecond resolution observations to tackle the nature of the water emission in Arp 220. ALMA Band 5 science verification observations of the 183 GHz H2O 313 − 220 line, in conjunction with new ALMA Band 7 H2O 515 − 422 data at 325 GHz, and supplementary 22 GHz H2O 616 − 523 VLA observations, are used to better constrain the parameter space in the excitation modeling of the water lines. Results. We detect 183 GHz H2O and 325 GHz water emission toward the two compact nuclei at the center of Arp 220, being brighter in Arp 220 West. The emission at these two frequencies is compared to previous single-dish data and does not show evidence of variability. The 183 and 325 GHz lines show similar spectra and kinematics, but the 22 GHz profile is significantly different in both nuclei due to a blend with an NH3 absorption line. Conclusions. Our findings suggest that the most likely scenario to cause the observed water emission in Arp 220 is a large number of independent masers originating from numerous star-forming regions.

galaxies: individual: Arp 220 / galaxies: ISM / galaxies: starburst / ISM: molecules


Sabine König

Astronomy and Plasmaphysics

S. Martín

Atacama Large Millimeter-submillimeter Array (ALMA)

European Southern Observatory Santiago

Sebastien Muller

Chalmers, Earth and Space Sciences, Onsala Space Observatory

Jose Cernicharo

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

K. Sakamoto

Academia Sinica

Laura Zschaechner

Max Planck Society

E. M. Humphreys

European Southern Observatory (ESO)

Tony Mroczkowski

European Southern Observatory (ESO)

Melanie Krips

Institut de Radioastronomie Millimétrique (IRAM)

Maud Galametz

The French Alternative Energies and Atomic Energy Commission (CEA)

European Southern Observatory (ESO)

Susanne Aalto

Astronomy and Plasmaphysics

Wouter Vlemmings

Astronomy and Plasmaphysics

Jürgen Ott

National Radio Astronomy Observatory Socorro

D. S. Meier

New Mexico Institute of Mining and Technology

A. Fuente

Spanish National Observatory (OAN)

S. G. Burillo

Spanish National Observatory (OAN)

Roberto Neri

Institut de Radioastronomie Millimétrique (IRAM)

Astronomy and Astrophysics

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

Vol. 602 42- 30331

Subject Categories

Astronomy, Astrophysics and Cosmology


Basic sciences



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