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arXiv · 1704.05278

First detection of the 448 GHz H2O transition in space

M. Pereira-Santaella·E. González-Alfonso·A. Usero·S. García-Burillo·J. Martín-Pintado·L. Colina·A. Alonso-Herrero·S. Arribas·S. Cazzoli·F. Rico·D. Rigopoulou·T. Storchi Bergmann
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Abstract

We present the first detection of the ortho-H2O 4_23-3_30 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 4_23-3_30 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 4_23-3_30 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 (tau_100{\mu}m > 1, N_H > 1e24 cm-2) required to efficiently excite it.

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M. Pereira-Santaella, E. González-Alfonso, A. Usero, S. García-Burillo, J. Martín-Pintado, L. Colina, A. Alonso-Herrero, S. Arribas, S. Cazzoli, F. Rico, D. Rigopoulou, T. Storchi Bergmann. 2017-04-18. First detection of the 448 GHz H2O transition in space. https://doi.org/10.1051/0004-6361%2F201730851

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