Volume 601, May 2017
|Number of page(s)||4|
|Published online||03 May 2017|
First detection of the 448 GHz H2O transition in space
1 Department of Physics, University of Oxford, Keble Road, Oxford, OX1 3RH, UK
2 Universidad de Alcalá, Departamento de Física y Matemáticas, Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain
3 Observatorio Astronómico Nacional (OAN-IGN)-Observatorio de Madrid, Alfonso XII, 3, 28014 Madrid, Spain
4 Centro de Astrobiología (CSIC/INTA), Ctra de Torrejón a Ajalvir, km 4, 28850 Torrejón de Ardoz, Madrid, Spain
5 Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía, s/n, 18008 Granada, Spain
6 Universidade Federal do Rio Grande do Sul, Instituto de Física, CP 15051, Porto Alegre 91501-970, RS, Brazil
Received: 22 March 2017
Accepted: 18 April 2017
We present the first detection of the ortho-H2O 423 − 330 transition at 448 GHz in space. We observed this transition in the local (z = 0.010) luminous infrared (IR) galaxy ESO 320-G030 (IRAS F11506-3851) using the Atacama Large Millimeter/submillimeter Array (ALMA). The water 423 − 330 emission, which originates in the highly obscured nucleus of this galaxy, is spatially resolved over a region of ~65 pc in diameter and shows a regular rotation pattern compatible with the global molecular and ionized gas kinematics. The line profile is symmetric and well fitted by a Gaussian with an integrated flux of 37.0 ± 0.7 Jy km s-1. Models predict this water transition as a potential collisionally excited maser transition. On the contrary, in this galaxy, we find that the 423 − 330 emission is primarily excited by the intense far-IR radiation field present in its nucleus. According to our modeling, this transition is a probe of deeply buried galaxy nuclei thanks to the high dust optical depths (τ100μm> 1, NH> 1024 cm-2) required to efficiently excite it.
Key words: galaxies: ISM / galaxies: nuclei / infrared: galaxies / ISM: molecules
© ESO, 2017
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