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First detection of the 448 GHz H2O transition in space.

Authors :: Pereira-Santaella, M.
González-Alfonso, E.
Usero, A.
García-Burillo, S.
Martín-Pintado, J.
Colina, L.
Alonso-Herrero, A.
Arribas, S.
Cazzoli, S.
Rico, F.
Rigopoulou, D.
Bergmann, T. Storchi
Source :: Astronomy & Astrophysics / Astronomie et Astrophysique; May2017, Vol. 601, p1-4, 4p
Publication Year :: 2017
Abstract: We present the first detection of the ortho-H<subscript>2</subscript>O 4<subscript>23</subscript> - 3<subscript>30</subscript> 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<subscript>23</subscript> - 3<subscript>30</subscript> 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<superscript>-1</superscript>. 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 (t100µm> 1, NH> 10<superscript>24</superscript> cm<superscript>-2</superscript>) required to efficiently excite it. [ABSTRACT FROM AUTHOR]