F. F. S. van der Tak, S. Aalto, and R. Meijerink,
reported on the
Detection of Extragalactic H₃O⁺,
Astron. Astrophys. 477, L5–L8 (2008).
The J_K^v_t = 3₂⁺ – 2₂^– at 364797.427 MHz has been detected unambiguously in emission in the starburst galaxy M 82 and in the ultraluminous infrared galaxy (ULIRG) Arp 220 using the JCMT. Thus far, this is the only transition detected. Thus, the detection may be viewed with some caution. The detection in the ISM (see respective section) started out similarly. Moreover, no line overlap with a line of an unknown seems possible. Therefore, the detection is probably quite secure.

S. Aalto, F. Costagliola, F. F. S. van der Tak, and R. Meijerink,
found in addition
H₃O⁺ Line Mmission from Starbursts and AGNs,
Astron. Astrophys. 527, Art. No. A69 (2011).
Transition and telescope were the same as above. IC 342, NGC 253, and NGC 4418 are members of the former group of galaxies, NGC 1068, also known as M 77, and NGC 6240 belong to the latter.

E. González-Alfonso, J. Fischer, S. Bruderer, et al.
reported on
Excited OH⁺, H₂O⁺, and H₃O⁺ in NGC 4418 and Arp 220,
Astron. Astrophys. 550, Art. No. A25 (2013);
using PACS on board of the Herschel satellite. Very highly excited rotation-inversion transitions were detected in both sources. In addition extensive metastable pure inversion transitions (up to J = K = 12 with an upper state energy of more than 1500 K) were detected in Arp 220. The hottest components diplay rotational temperatures of about 500 K and 550 K for NGC 4418 and Arp 220, respectively.

Contributor(s): H. S. P. Müller, 01/2008; 04, 2013.