Infrared characters of host galaxies with H2O megamaser

Infrared characters of all the host galaxies with the H2O megamaser have be en studied. The most striking feature is the anticorrelation of S(60)/S(100 ) versus S(12)/S(25), and S(25)/S(60) versus S(12)/S(25). The anticorrelati on in the flux density ratio can been explained by coexistence of large and very small dust particles. The latter, which are heated by absorption of s ingle photon, are believed to be responsible for the bulk of 12 mum radiati on. If the photon energy of the host galaxy is small, this implies large S( 12)/S(25) and small S(60)/S(100). However, when photon energy density becom es larger, the infrared spectrum will peak at wavelengths less than or equa l to 100 mum and enhance emission at 25 mum. As a consequence small S(12)/S (25) and large S(60)/S(100) are observed.