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Signatures of the Many Supermassive Black Hole Mergers in a Cosmologically Forming Massive Early-Type Galaxy

Authors :
Mannerkoski, Matias
Johansson, Peter H.
Rantala, Antti
Naab, Thorsten
Liao, Shihong
Rawlings, Alexander
Source :
ApJ 929 167 (2022)
Publication Year :
2021

Abstract

We model here the merger histories of the supermassive black hole (SMBH) population in the late stages of a cosmological simulation of a $\sim 2 \times 10^{13} M_\odot$ galaxy group. The gravitational dynamics around the several tens of SMBHs ($M_{\bullet} \gtrsim 7.5\times 10^7 M_\odot$) hosted by the galaxies in the group is computed at high accuracy using regularized integration with the KETJU code. The 11 SMBHs which form binaries and hierarchical triplets eventually merge after hardening through dynamical friction, stellar scattering, and gravitational wave (GW) emission. The binaries form at eccentricities of $e \sim 0.3$-$0.9$, with one system evolving to a very high eccentricity of $e = 0.998$, and merge on timescales of a few tens to several hundred megayears. During the simulation the merger-induced GW recoil kicks eject one SMBH remnant from the central host galaxy. This temporarily drives the galaxy off the $M_{\bullet}$-$\sigma_{\star}$ relation, however the galaxy returns to the relation due to subsequent galaxy mergers, which bring in new SMBHs. This showcases a possible mechanism contributing to the observed scatter of the $M_{\bullet}$-$\sigma_{\star}$ relation. Finally, we show that Pulsar Timing Arrays and LISA would be able to detect parts of the GW signals from the SMBH mergers that occur during the $\sim 4\,\mathrm{Gyr}$ time span simulated with KETJU.<br />Comment: 12 pages, 5 figures, 1 table. Accepted to ApJ. Added extended discussion and more detail on the properties of the simulated galaxies

Details

Database :
arXiv
Journal :
ApJ 929 167 (2022)
Publication Type :
Report
Accession number :
edsarx.2112.03576
Document Type :
Working Paper
Full Text :
https://doi.org/10.3847/1538-4357/ac5f0b