A Near-Neighbor Statistical Survey of the Environments of Galaxies with Water Masers

Water mega-masers provide crucial tools for accurate determination ofmasses of black holes lurking in galaxy centers, and of extragalacticdistances without the need for indirect cosmological assumptions. Current searches have detected masers in only 3 - 4% of the galaxies surveyed and require refinement of their survey criteria. Motivated by current models linking galaxy environment and black hole accretion and the possibility that maser activity correlates with black hole accretion, we conducted a study of the properties of the small and large-scale environments of galaxies hosting masers. Using samples of galaxies with and without maser detections provided by the Megamaser Cosmology Project, together with the Sloan Digital Sky Survey spectroscopic observations, we present a comparative analysis of near-neighbor statistics and their properties, which include distances to the n-th neighbors as well as neighbor counts within fixed volumes, and optical colors and absolute brightness distributions. We show evidence that the environments of the mega-masers in particular differ from those of galaxies where maser activity was not detected, with the mega-masers possiblyprefering the lower density regions. Nevertheless, the trends presented by various measures of the environmental properties of maser and non-maser systems remain complicated. A better understanding of the factors that closely connect with the masing conditions and overall activity can be achieved with higher number statistics, possibly through conducting near-neighbor investigations involving photometric redshift measurements, that allow characterization of neighboring systems at much fainter levels.