Identifying the host galaxy of gravitational wave signals

One of the goals of the current LIGO-GEO-Virgo science run is to identify transient gravitational wave (GW) signals in near real time to allow follow-up electromagnetic (EM) observations. An EM counterpart could increase the confidence of the GW detection and provide insight into the nature of the source. Current GW-EM campaigns target potential host galaxies based on overlap with the GW sky error box. We propose a new statistic to identify the most likely host galaxy, ranking galaxies based on their position, distance, and luminosity. We test our statistic with Monte Carlo simulations of GWs produced by coalescing binaries of neutron stars and black holes, one of the most promising sources for ground-based GW detectors. Considering signals accessible to current detectors, we find that when imaging a single galaxy, our statistic correctly identifies the true host $\sim 20\%$ to $\sim 50\%$ of the time, depending on the masses of the binary components. With five narrow-field images the probability of imaging the true host increases from $\sim 50\%$ to $\sim 80\%$. When collectively imaging groups of galaxies using large field-of-view telescopes, the probability improves from $\sim 30\%$ to $\sim 60\%$ for a single image and from $\sim 70\%$ to $\sim 90\%$ for five images. For the advanced generation of detectors (circa $2015+$), and considering binaries within 100 Mpc (the reach of the galaxy catalogue used), the probability is $\sim 40\%$ for one narrow-field image, $\sim 75\%$ for five narrow-field images, $\sim 65\%$ for one wide-field image, and $\sim 95\%$ for five wide-field images, irrespective of binary type.

Figure 1

Narrow field-of-view case. The probability of imaging the true host galaxy for each type of binary system versus the number of images taken. The shaded regions denote the 1-sigma uncertainty in the probability estimate.

Figure 2

Wide field-of-view case. The probability of imaging the true host galaxy for each type of binary system versus the number of images taken. The shaded regions denote the 1-sigma uncertainty in the probability estimate.