|19th of September 2019|
|Excited extragalactic OH|
|by Eisner et al.|
Centimeter-wave transitions are important counterparts to the
rotational mm-wave transitions usually observed to study gas in
star-forming regions. However, given their relative weakness, these
transitions have historically been neglected. Eisner et al. present Australia
Telescope Compact Array 4cm- and 15mm-band spectral line observations
of nine nearby star-forming galaxies.
Thirteen different molecular lines are detected across
the sample from OH, NH3, H2O, H2CO, and c-C3H2, as well as 18 radio
recombination lines (RRLs) in NGC 253. Excited OH absorption is
detected at rest-frame frequencies of
23.81762 and 23.82662 GHz
towards NGC 4945 and Circinus; only the third and fourth
extragalactic detections of this (J=9/2) OH transition.
Circinus’s OH lines are blueshifted from the
systemic velocity by ~35 km s−1 , while NGC 4945’s are redshifted by
~100 km/s, with the latter likely indicating infall onto
The images above show the profiles of the detected OH lines in NGC 4945 and Circinus. The blue vertical lines show the systemic velocities of the galaxies, while the shaded regions represent the approximate extents of the lines. Both hyperfine components are seen in each figure. More details are give in the paper, published in the Astrophysical Journal.