HI absorption in the gigamaser galaxy TXS 2226-184 and the relation between HI absorption and water emission

Abstract

We report on the discovery of H i in absorption toward the gigamaser galaxy TXS 2226-184 using the Very Large Array. The absorption appears to consist of two components—one with a width of 125 km s^-1 and one broader (420 km s^-1)—both toward the compact radio source in the nucleus of the galaxy. Based on these large velocity widths, we suggest that the H i absorption is produced in the central parsecs of the galaxy, on a scale similar to that which gives rise to the water maser emission. This brings to eight the number of galaxies known to exhibit both water masers and H i absorption. We explore the relationship between these two phenomena and present a physically motivated (but unfruitful) search for water maser emission in five radio galaxies known to exhibit strong Hi absorption (Refer to PDF file for exact formulas).