We assess the effect of simulated active galactic nuclei (AGNs) on the color and morphology measurements of their host galaxies. To test the morphology measurements, we select a sample of galaxies not known to host AGNs and add a series of point sources scaled to represent specified fractions of the observed V band light detected from the resulting systems; we then compare morphology measurements of the simulated systems to measurements of the original galaxies. AGN contributions >20% bias most of the morphology measurements tested, though the extent of the apparent bias depends on the morphological characteristics of the original galaxies. We test color measurements by adding to non-AGN galaxy spectra a quasar spectrum scaled to contribute specified fractions of the rest-frame B band light detected from the resulting systems. A quasar fraction of 5% can move the NUV-r color of an elliptical galaxy from the UV-optical red sequence to the green valley, and 20% can move it into the blue cloud. Combining the color and morphology results, we find that a galaxy/AGN system with an AGN contribution >20% may appear bluer and more bulge-dominated than the underlying galaxy.

We conclude that (1) bulge-dominated, E/S0/Sa, and early-type morphology classifications are accurate for AGN host galaxies, unless the AGN manifests itself as a well-defined point source; and (2) although highly unobscured AGNs, such as the quasar used for our experiments, can significantly bias the measured colors of AGN host galaxies, it is possible to identify such systems by searching optical images of the host for the presence of a point source and/or measuring the level of nuclear obscuration.

Christy Pierce .works as a postdoctoral researcher at Georgia Tech's Center for Relativistic Astrophysics. She received her Ph.D. from the University of California, Santa Cruz, earlier this year. Her research focuses on the relationships between the growth of supermassive black holes (AGNs) and the galaxies in which they reside.