SIMBAD references

To shed light onto the circumnuclear environment of 22 GHz (λ ∼ 1.3 cm) H₂ O maser galaxies, we have analyzed some of their multiwavelength properties, including the far-infrared luminosity (FIR), the luminosity of the [O_III] λ5007 emission line, the nuclear X-ray luminosity, and the equivalent width (EW) of the neutral iron Kα emission line (EW (K_α)). Our statistical analysis includes a total of 85 sources, most of them harboring an active galactic nucleus (AGN). There are strong anticorrelations between EW (K_α) and two "optical thickness parameters," i.e., the ratios of the X-ray luminosity versus the presumably more isotropically radiated [O_III] and FIR luminosities. Based on these anticorrelations, a set of quantitative criteria, EW (K_α)>300 eV, L_2–10keV < 2L_[OIII_], and L_FIR>600 L_2-10 keV_ can be established for Compton-thick nuclear regions. Eighteen H₂ O maser galaxies belong to this category. There are no obvious correlations between the EW (K_α), the [O_III] luminosity, and the isotropic H₂ O maser luminosity. When comparing samples of Seyfert 2s with and without detected H₂ O maser lines, there seem to exist differences in EW (K_α) and the fraction of Compton-thick nuclei. This should be studied further. For AGN masers alone, there is no obvious correlation between FIR and H₂ O maser luminosities. However, including masers associated with star-forming regions, a linear correlation is revealed. Overall, the extragalactic FIR-H₂ O data agree with the corresponding relation for Galactic maser sources, extrapolated by several orders of magnitude to higher luminosities.