While the first “seeds” of supermassive black holes (BH) can range from $\sim 10^2-10^6 \rm ~{\rm M}_{\odot }$, the lowest mass seeds ($\lesssim 10^3~\rm {\rm M}_{\odot }$) are inaccessible to most cosmological simulations due to resolution limitations. We present our new BRAHMA simulations that use a novel flexible seeding approach to predict the $z\ge 7$ BH populations for low-mass seeds. We ran two types of boxes that model $\sim 10^3~\rm {\rm M}_{\odot }$ seeds using two distinct but mutually consistent seeding prescriptions at different simulation resolutions. First, we have the highest resolution $[9~\mathrm{Mpc}]^3$ (BRAHMA-9-D3) boxes that directly resolve $\sim 10^3~\rm {\rm M}_{\odot }$ seeds and place them within haloes with dense, metal-poor gas. Second, we have lower resolution, larger volume $[18~\mathrm{Mpc}]^3$ (BRAHMA-18-E4), and $\sim [36~\mathrm{Mpc}]^3$ (BRAHMA-36-E5) boxes that seed their smallest resolvable $\sim 10^4~\&~10^5~\mathrm{{\rm M}_{\odot }}$ BH descendants using new stochastic seeding prescriptions calibrated using BRAHMA-9-D3. The three boxes together probe key BH observables between $\sim 10^3\,\mathrm{ and}\,10^7~\rm {\rm M}_{\odot }$. The active galactic nuclei (AGN) luminosity function variations are small (factors of $\sim 2-3$) at the anticipated detection limits of potential future X-ray facilities ($\sim 10^{43}~ \mathrm{ergs~s^{-1}}$ at $z\sim 7$). Our simulations predict BHs $\sim 10-100$ times heavier than the local $M_*$ versus $M_{\mathrm{ bh}}$ relations, consistent with several JWST-detected AGN. For different seed models, our simulations merge binaries at $\sim 1-15~\mathrm{kpc}$, with rates of $\sim 200-2000$ yr−1 for $\gtrsim 10^3~\rm {\rm M}_{\odot }$ BHs, $\sim 6-60$ yr−1 for $\gtrsim 10^4~\rm {\rm M}_{\odot }$ BHs, and up to $\sim 10$ yr−1 amongst $\gtrsim 10^5~\rm {\rm M}_{\odot }$ BHs. These results suggest that Laser Interferometer Space Antenna mission has promising prospects for constraining seed models.
Stellar-mass black holes (BHs) can be retained in globular clusters (GCs) until the present. Simulations of GC evolution find that the relaxation driven mass-loss rate is elevated if BHs are present, especially near dissolution. We capture this behaviour in a parametrized mass-loss rate, bench marked by results from N-body simulations, and use it to evolve an initial GC mass function (GCMF), similar to that of young massive clusters in the Local Universe, to an age of 12 Gyr. Low-metallicity GCs ([Fe/H] ≲ −1.5) have the highest mass-loss rates, because of their relatively high BH masses, which combined with their more radial orbits and stronger tidal field in the past explains the high turnover mass of the GCMF ($\sim 10^5\, {\rm M}_\odot$ ) at large Galactic radii ($\gtrsim 10\, {\rm kpc}$ ). The turnover mass at smaller Galactic radii is similar because of the upper mass truncation of the initial GCMF and the lower mass-loss rate due to the higher metallicities. The density profile in the Galaxy of mass lost from massive GCs ($\gtrsim 10^{5}\, {\rm M}_\odot$ ) resembles that of nitrogen-rich stars in the halo, confirming that these stars originated from GCs. We conclude that two-body relaxation is the dominant effect in shaping the GCMF from a universal initial GCMF, because including the effect of BHs reduces the need for additional disruption mechanisms.
more » « less- Award ID(s):
- 1909063
- NSF-PAR ID:
- 10413883
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 522
- Issue:
- 4
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 5340-5357
- Size(s):
- p. 5340-5357
- Sponsoring Org:
- National Science Foundation
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