The incidence and properties of Active Galactic Nuclei ( AGN ) in the field , groups , and clusters can provide new information about how these objects are triggered and fueled , similar to how these environments have been employed to study galaxy evolution .
We have obtained new XMM-Newton observations of seven X-ray selected groups and poor clusters with 0.02 < z < 0.06 for comparison with previous samples that mostly included rich clusters and optically-selected groups .
Our final sample has ten groups and six clusters in this low-redshift range ( split at a velocity dispersion of \sigma = 500 \textrm { km s } ^ { -1 } ) .
We find that the X-ray selected AGN fraction increases from f _ { A } ( L _ { X } > 10 ^ { 41 } ;M _ { R } < M _ { R } ^ { * } +1 ) = 0.047 ^ { +0.023 } _ { -0.016 } in clusters to 0.091 ^ { +0.049 } _ { -0.034 } for the groups ( 85 % significance ) , or a factor of two , for AGN above an 0.3-8keV X-ray luminosity of 10 ^ { 41 } \textrm { erg s } ^ { -1 } hosted by galaxies more luminous than M _ { R } ^ { * } +1 .
The trend is similar , although less significant , for a lower-luminosity host threshold of M _ { R } = -20 mag .
For many of the groups in the sample we have also identified AGN via standard emission-line diagnostics and find that these AGN are nearly disjoint from the X-ray selected AGN .
Because there are substantial differences in the morphological mix of galaxies between groups and clusters , we have also measured the AGN fraction for early-type galaxies alone to determine if the differences are directly due to environment , or indirectly due to the change in the morphological mix .
We find that the AGN fraction in early-type galaxies is also lower in clusters f _ { A,n > 2.5 } ( L _ { X } > 10 ^ { 41 } ;M _ { R } < M _ { R } ^ { * } +1 ) = 0.048 ^ { +0.028 } _ { -0.019 } compared to 0.119 ^ { +0.064 } _ { -0.044 } for the groups ( 92 % significance ) , a result consistent with the hypothesis that the change in AGN fraction is directly connected to environment .