The Consequences of Rubin Observatory Time-Domain Survey Design and Host-Galaxy Contamination on the Identification of Binary Supermassive Black Holes

TL;DR

This study assesses how survey design and host-galaxy contamination impact the detection of binary supermassive black holes in time-domain surveys, highlighting the importance of longer observation durations for improved detection accuracy.

Contribution

It provides a simulation-based analysis of how host contamination and survey parameters affect binary SMBH detection, emphasizing the critical role of extended monitoring durations.

Findings

Host-galaxy contamination increases false positives and reduces binary parameter accuracy.

Longer survey durations significantly improve binary detection and parameter recovery.

Extending light curve duration from 5 to 20 years greatly enhances detection success.

Abstract

Binary supermassive black holes (SMBHs) are consequences of galaxy mergers and dominate the low-frequency gravitational wave background. Finding binary SMBHs in existing time-domain observations has proven difficult, as their periodic, electromagnetic signals can be confused with the natural variability of single quasars. In this work, we investigate the effects of host-galaxy contamination and survey design (cadence and duration) on the detectability of binary SMBHs with the upcoming Rubin Observatory Legacy Survey of Space and Time (LSST). We simulate millions of LSST light curves of single and binary quasars, with a distribution of quasar and host-galaxy properties motivated by empirical observations and the anticipated LSST detection space. We then apply simple sinusoidal curve fits as a potential, computationally inexpensive detection method. We find that host-galaxy contamination will increase false-positive rates and decrease binary parameter recovery rates. Lower mass, lower luminosity binary systems are most likely to be negatively affected by host galaxy contamination. We also find that monitoring duration affects binary detection more than survey effective cadence for this detection method. As the light curve duration increases, false-positive rates are suppressed and binary parameter recovery rates, especially for binary period, are improved. Increasing the light curve duration from 5 to 10 yrs shows the most dramatic improvement for successful binary detection and false-positive rejection, with additional improvement from extending the light curve duration to 20 yrs. The observation duration increase is especially critical for recovering binary periods that are longer than a decade.