Radio continuum properties of OH megamaser galaxies

Sotnikova Yu V., Zhongzu Wu, Mufakharov T. V., Mikhailov A. G., Mingaliev M. G., Erkenov A. K., Semenova T. A., Bursov N. N., Udovitskiy R. Y., Stolyarov V. A., Tsybulev P. G., Chen Y. J., Zhang J. S., Shen Z., Jiang D. R.

We present a study of the radio continuum properties of two luminous/ultraluminous infrared galaxy samples: the OH megamaser (OHM) sample (74 objects) and the control sample (128 objects) without detected maser emission. We carried out pilot observations for 140 objects with the radio telescope RATAN-600 at 1.2, 2.3, 4.7, 8.2, 11.2, and 22.3 GHz in 2019-2021. The OHM sample has two times more flat-spectrum sources (32 per cent) than the control sample. Steep radio spectra prevail in both samples. The median spectral index at 4.7 GHz α_4.7 = -0.59 for the OHM sample, and α_4.7 = -0.71 for the non-OHM galaxies. We confirm a tight correlation of the far-infrared (FIR) and radio luminosities for the OHM sample. We found correlations between isotropic OH line luminosity L_OH and the spectral index α_4.7 (ρ=0.26, p-val.=0.04) and between L_OH and radio luminosity P_1.4 (ρ=0.35, p-val.=0.005). Reviewing subsamples of masers powered by active galactic nuclei and star formation revealed insignificant differences for their FIR and radio properties. Nonetheless, AGN-powered galaxies exhibit larger scatter in a range of parameters and their standard deviations. The similarities in the radio and FIR properties in the two samples are presumably caused by the presence of a significant amount of AGN sources in both samples (47 and 30 per cent in the OHM and control samples) and/or possibly by the presence of undetected OH emission sources in the control sample. Original →