2025/03/31 by Wang, Bonny Y., Zhou, Yihao, Chen, William +5 · 1 citation
#Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences
paper · doi:10.48550/arxiv.2503.24304
We use the ASTRID cosmological simulation to forecast massive black hole (MBH) mergers detectable by Laser Interferometer Space Antenna (LISA) down to z=0. ASTRID directly models MBH dynamical friction, allowing a realistic tracking of their trajectory. It also incorporates relatively low-mass MBH seeds down to 5×104 M\odot, providing a more complete picture of LISA MBH mergers. We find that LISA MBH mergers initially have high eccentricities, peaking around e0 = 0.8 across all redshifts. Accounting for this boosts the event rate from 5.6 yr-1 (if circular orbits are assumed) to 10.5 yr-1. This enhancement is largely due to additional inspiral sources that will coalesce after LISA's observation, which constitute 46% of detected events.This underscores the importance of LISA's sensitivity to the early inspiral phase, especially for eccentric binaries that emit gravitational waves across a wider frequency band. Most LISA events in ASTRID arise from MBH∼105-6 M_\odot, low-redshift (z<2) and low mass-ratio (q∼0.01-0.1) mergers. Accounting for eccentricity broadens the detectable MBH mass range up to 109 M_\odot and shifts the peak of detectable mergers to a lower redshift z\rm peak=0.8. This implies that the most massive LISA events may also be PTA sources. We predict LISA events to be in various galaxy environments, including many low-mass satellite galaxies. The electromagnetic (EM) counterparts of most LISA sources have active galactic nuclei (AGN) luminosities L\rm bol>1042 erg s-1, albeit only 1% with >1044 erg s-1. The brightest AGN are those associated with the rare LISA/PTA events with M\rm BH>108 M_\odot.