Australia Telescope Observations of Excited-State OH Transitions in NGC4945

Details Australia Telescope Observations of Excited-State OH Transitions in NGC4945 Australia Telescope Observations of Excited-State OH Transitions in NGC4945

Aug 1990

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990mnras.245..665w&link_type=abstract

Monthly Notices of the Royal Astronomical Society, Vol. 245, NO.4/AUG15, P. 665, 1990

Astronomy and Astrophysics

Astronomy

21

Scientific paper

Several antennas of the Australia Telescope's compact array have been used to produce the first AT spectral-line images, which are of OH excited-state transitions towards the southern edge-on spiral galaxy NGC 4945. For the 6030- and 6035-MHz transitions of the ^2pi_3/2_, J=5/2 state, well- defined line absorption was detected against the 6 x 2 arcsec^2^ radio continuum nucleus of the galaxy. The line profiles are wide, with heliocentric radial velocities extending from 350 to 750 km s^-1^, and with overall shapes similar to the corresponding ground-state transitions at 1665 and 1667 MHz. The distribution of the line-to-continuum ratio maximizes at about 650 km s^-1^, with a value of 0.07 for the 6035-MHz transition. A comparison with previous 1667-MHz results yields an OH-cloud temperature of 36 K. The position of the absorption moves systematically across the continuum with its velocity in the manner of a rotating molecular cloud. In contrast to the results for several OH megamaser galaxies, no transitions of the ^2pi_1/2_, J=1/2 state at 4.7 GHz were detected down to flux-density levels of 0.01 Jy. The absence of these transitions is attributed to insufficient far-infrared excitation by the nucleus.

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