First detection of the 448 GHz H2O transition in space
  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.
