Expected Host Galaxy Properties of PTA Detectable Massive Black Hole Binaries

Abstract

Massive black hole binaries (MBHB) produce gravitational waves (GW) that will be detectable with pulsar timing arrays within the next few years. We determine the properties of the host galaxies of MBHB at the time they are producing detectable GW. The population of MBHB systems we evaluate is from the Illustris cosmological simulations taken in tandem with post processing semi-analytic models of environmental factors in the evolution of binaries. Upon evolving to the frequency regime detectable by pulsar timing arrays, we calculate the detection probability of each system using a variety of different values for red and white noise. We average over multiple realizations of the universe by re-sampling the host galaxy properties using a kernel density estimator to approximate the statistical distributions of the universe. Excitingly, we find that detectable systems have host galaxies that are clearly distinct from the overall population. With conservative noise factors, we found that stellar metallicity, for example, peaks at approximately twice solar metallicity as opposed to the total population of galaxies which peaks at approximately solar metallicity. Additionally, the most detectable systems are brighter and more red in color than the overall population. These results can be used to develop effective search strategies for identifying host galaxies and electromagnetic counterparts following GW detections.