Where to search for supermassive binary black holes

TL;DR

This paper discusses strategies for detecting supermassive binary black holes by analyzing spectral signatures and emphasizes the importance of time-domain spectroscopic surveys to identify periodic variability indicative of binary activity.

Contribution

It proposes observational strategies focusing on spectral signatures and highlights the potential of time-domain surveys for discovering supermassive binary black holes.

Findings

Preliminary analysis of a flux-limited quasar sample.

Spectroscopic clues suggestive of binary activity.

Time-domain surveys can reveal periodic variability.

Abstract

Supermassive binary black holes (SMBBHs) are the anticipated byproducts of galaxy mergers and play a pivotal role in shaping galaxy evolution, gravitational wave emissions, and accretion physics. Despite their theoretical prevalence, direct observational evidence for SMBBHs remains elusive, with only a handful of candidates identified to date. This paper explores optimal strategies and key environments for locating SMBBHs, focusing on observational signatures in the broad Balmer lines. We present a preliminary analysis on a flux-limited sample of sources belonging to an evolved spectral type along the quasar main sequence, and we discuss the spectroscopic clues indicative of binary activity and highlight the critical role of time-domain spectroscopic surveys in uncovering periodic variability linked to binary systems.