Having conducted a search for the λ ∼ 1.3 cm (22 GHz) water vapor line towards galaxies with nuclear activity, large nuclear column densities or high infrared luminosities, we present H 2 O spectra for NGC 2273, UGC 5101, and NGC 3393 with isotropic luminosities of 7, 1500, and 400 L . The H 2 O maser in UGC 5101 is by far the most luminous yet found in an ultraluminous infrared galaxy. NGC 3393 reveals the classic spectrum of a "disk maser", represented by three distinct groups of Doppler components. As in all other known cases except NGC 4258, the rotation velocity of the putative masing disk is well below 1000 km s −1 . Based on the literature and archive data, X-ray absorbing column densities are compiled for the 64 galaxies with reported maser sources beyond the Magellanic Clouds. For NGC 2782 and NGC 5728, we present Chandra archive data that indicate the presence of an active galactic nucleus in both galaxies. Modeling the hard nuclear X-ray emission, NGC 2782 is best fit by a high energy reflection spectrum with N H > ∼ 10 24 cm −2 . For NGC 5728, partial absorption with a power law spectrum indicates N H ∼ 8 × 10 23 cm −2 . The correlation between absorbing column and H 2 O emission is analyzed. There is a striking difference between kilo-and megamasers with megamasers being associated with higher column densities. All kilomasers (L H 2 O < 10 L ) except NGC 2273 and NGC 5194 are Compton-thin, i.e. their absorbing columns are <10 24 cm −2 . Among the H 2 O megamasers, 50% arise from Compton-thick and 85% from heavily obscured (>10 23 cm −2 ) active galactic nuclei. These values are not larger but consistent with those from samples of Seyfert 2 galaxies not selected on the basis of maser emission. The similarity in column densities can be explained by small deviations in position between maser spots and nuclear X-ray source and a high degree of clumpiness in the circumnuclear interstellar medium.

We present observations of the C-band 1 10 − 1 11 (4.8 GHz) and Ku-band 2 11 − 2 12 (14.5 GHz) K-doublet lines of H 2 CO and the C-band 1 10 − 1 11 (4.6 GHz) line of H 2 13 CO toward a large sample of Galactic molecular clouds, through the Shanghai Tianma 65-m radio telescope (TMRT). Our sample with 112 sources includes strong H 2 CO sources from the TMRT molecular line survey at C-band and other known H 2 CO sources. All three lines are detected toward 38 objects (43 radial velocity components) yielding a detection rate of 34%. Complementary observations of their continuum emission at both C-and Ku-bands were performed. Combining spectral line parameters and continuum data, we calculate the column densities, the optical depths and the isotope ratio H 2 12 CO/H 2 13 CO for each source. To evaluate photon trapping caused by sometimes significant opacities in the main isotopologue's rotational mm-wave lines connecting our measured K-doublets, and to obtain 12 C/ 13 C abundance ratios, we used the RADEX non-LTE model accounting for radiative transfer effects. This implied the use of the new collision rates from Wiesenfeld & Faure (2013). Also implementing distance values from trigonometric parallax measurements for our sources, we obtain a linear fit of 12 C/ 13 C = (5.08±1.10)D GC + (11.86±6.60), with a correlation coefficient of 0.58. D GC refers to Galactocentric distances. Our 12 C/ 13 C ratios agree very well with the ones deduced from CN and C 18 O but are lower than those previously reported on the basis of H 2 CO, tending to suggest that the bulk of the H 2 CO in our sources was formed on dust grain mantles and not in the gas phase.

Aims. Magnetic fields exist on all scales in our Galaxy. There is a controversy about whether the magnetic fields in molecular clouds are preserved from the permeated magnetic fields in the interstellar medium (ISM) during cloud formation. We investigate this controversy using available data in the light of the newly revealed magnetic field structure of the Galactic disk obtained from pulsar rotation measures (RMs). Methods. We collected measurements of the magnetic fields in molecular clouds, including Zeeman splitting data of OH masers in clouds and OH or HI absorption or emission lines of clouds themselves.Results. The Zeeman data show structures in the sign distribution of the line-of-sight component of the magnetic field. Compared to the large-scale Galactic magnetic fields derived from pulsar RMs, the sign distribution of the Zeeman data shows similar large-scale field reversals. Previous such examinations were flawed in the over-simplified global model used for the large-scale magnetic fields in the Galactic disk. Conclusions. We conclude that the magnetic fields in the clouds may still "remember" the directions of magnetic fields in the Galactic ISM to some extent, and could be used as complementary tracers of the large-scale magnetic structure. More Zeeman data of OH masers in widely distributed clouds are required.