James Webb Space Telescope Feed Post

Date: 6/10/2024

Harvard ADS: Introducing the BRAHMA simulation suite: Signatures of low mass black hole seeding models in cosmological simulations

Paper abstract: While the first "seeds" of supermassive black holes (BH) can range from ~ 10^2-10^6 \rm ~{\rm M}_{\odot }, the lowest mass seeds (<~ 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 = 7 BH populations for low mass seeds. We ran two types of boxes that model ~ 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 Mpc]3 (BRAHMA-9-D3) boxes that directly resolve ~ 10^3~\rm {\rm M}_{\odot } seeds and place them within halos with dense, metal-poor gas. Second, we have lower-resolution, larger-volume [18 Mpc]3 (BRAHMA-18-E4) and ~[36 Mpc]3 (BRAHMA-36-E5) boxes that seed their smallest resolvable ~ 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 ~ 10^3-10^7~\rm {\rm M}_{\odot }. The AGN luminosity function variations are small (factors of ~2 - 3) at the anticipated detection limits of potential future X-ray facilities (~1043 ergs s-1 at z ~ 7). Our simulations predict BHs ~10 - 100 times heavier than the local M* vs Mbh relations, consistent with several JWST-detected AGN. For different seed models, our simulations merge binaries at ~1 - 15 kpc, with rates of ~200 - 2000 per year for \gtrsim 10^3~\rm {\rm M}_{\odot } BHs, ~6 - 60 per year for \gtrsim 10^4~\rm {\rm M}_{\odot } BHs, and up to ~10 per year amongst \gtrsim 10^5~\rm {\rm M}_{\odot } BHs. These results suggest that LISA mission has promising prospects for constraining seed models.