Abstract
Using the Effelsberg 100-m telescope, detections of four extragalactic water vapor masers are reported. Isotropic luminosities are ~50, 1000, 1 and 230 $L_{\odot}$ for Mrk 1066 (UGC 2456), Mrk 34, NGC 3556 and Arp 299, respectively. Mrk 34 contains by far the most distant and one of the most luminous water vapor megamasers so far reported in a Seyfert galaxy. The interacting system Arp 299 appears to show two maser hotspots separated by approximately 20´´. With these new results and even more recent data from Braatz et al. (2004, ApJ, 617, L29), the detection rate in our sample of Seyferts with known jet-Narrow Line Region interactions becomes 50% (7/14), while in star forming galaxies with high ($S_{\rm 100~\mu m}>50$ Jy) far infrared fluxes the detection rate is 22% (10/45). The jet-NLR interaction sample may not only contain “jet-masers” but also a significant number of accretion “disk-masers” like those seen in NGC 4258. A statistical analysis of 53 extragalactic H2O sources (excluding the Galaxy and the Magellanic Clouds) indicates (1) that the correlation between IRAS Point Source and H2O luminosities, established for individual star forming regions in the galactic disk, also holds for AGN-dominated megamaser galaxies; (2) that maser luminosities are not correlated with 60 μm/100 μm color temperatures; and (3) that only a small fraction of the luminous megamasers ($L_{\rm H_2O} > 100$ $L_{\odot}$) detectable with 100-m sized telescopes have so far been identified. The H2O luminosity function (LF) suggests that the number of galaxies with 1 $L_{\odot} < L_{\rm H_2O} < 10$ $L_{\odot}$, the transition range between “kilomasers” (mostly star formation) and “megamasers” (active galactic nuclei), is small. The overall slope of the LF, ~-1.5, indicates that the number of detectable masers is almost independent of their luminosity. If the LF is not steepening at very high maser luminosities and if it is possible to find suitable candidate sources, H2O megamasers at significant redshifts should be detectable even with present day state-of-the-art facilities.