We visually and quantitatively determine the host galaxy morphologies of 94 intermediate redshift ( 0.2 \leq z < 1.2 ) active galactic nuclei ( AGN ) , selected using Chandra X-ray and Spitzer mid-infrared data in the Extended Groth Strip .
Using recently developed morphology measures , the second-order moment of the brightest 20 \% of a galaxy ’ s flux ( M _ { 20 } ) and the Gini coefficient , we find that X-ray–selected AGN mostly reside in E/S0/Sa galaxies ( 53 ^ { +11 } _ { -10 } \% ) , while IR–selected AGN show no clear preference for host morphology .
X-ray–selected AGN hosts are members of close pairs more often than the field population by a factor of 3.3 \pm 1.4 , but most of these pair members appear to be undisturbed early-type galaxies and do not tend to show direct evidence of gravitational perturbations or interactions .
Thus , the activation mechanism for AGN activity remains unknown , even for pair members .