The ASTRID Simulation at z=0: from Massive Black Holes to Large-scale Structure

TL;DR

The paper presents z=0 results from ASTRID, a large-volume cosmological hydrodynamical simulation with 2×5500^3 particles in a ~370 Mpc box, spanning MBH masses from seeds to 2×10^11 M⊙ and tracking MBH growth, mergers, and feedback within a full-physics context. It demonstrates that MBH demographics and co-evolution with galaxies reproduce key observables, including the MBH mass function above 10^7 M⊙, the M_BH–M★ and M_BH–σ relations with realistic scatter, and an X-ray AGN luminosity function consistent with data for plausible radiative efficiencies. The galaxy population matches observational constraints on the GSMF and dust-attenuated LF, with realistic color bimodality and sSFR trends, though the knee of the GSMF is slightly underestimated likely due to the kinetic feedback threshold. The study also analyzes the abundance and clustering of groups and clusters, the SMHM relation, stellar mass budgets within halos, and the clustering of MBHs and galaxies, finding that MBHs with masses above ~10^8 M⊙ and galaxies with stellar masses above ~10^10.5 M⊙ are effective tracers of large-scale structure; the public data enable further MBH–cosmology experiments and multi-messenger studies.

Abstract

We present the $z=0$ results for the cosmological simulation ASTRID. Hosting $2\times 5500^3\approx$ 0.33 trillion particles in a box of $370\, {\rm Mpc}$ per side, ASTRID is one of the largest cosmological hydrodynamic simulations evolved to $z=0$. ASTRID features a large population of massive black holes (MBHs), covering a wide mass range $4\times10^{4}\sim 2\times 10^{11}\ M_{\odot}$. The adopted dynamical friction model provides a relatively accurate description of MBH dynamics, making ASTRID a powerful tool to study MBH growth and mergers in a cosmological context. ASTRID successfully captures the co-evolution of MBHs and their host galaxies, producing $M_{\rm BH}-M_{\star}$ and $M_{\rm BH}-σ$ relations in good agreement with observations. Notably, ASTRID generates scatter in these relations that is more consistent with observations than previous simulations, indicating a more realistic MBH diversity. The galaxy stellar mass function at $z=0$ is generally consistent with observational constraints. When dust attenuation is applied, the galaxy luminosity function also agrees well with observations, and the bimodality in galaxy colors is reproduced as well. ASTRID hosts a large population of massive galaxy groups and clusters: 7 halos have $M_{\rm 200c}>10^{15}\ M_{\odot}$, and 9709 halos have $M_{\rm 200c}>10^{13}\ M_{\odot}$. We quantify the stellar mass content in these halos, and find that the correlations between the stellar and halo mass match well with observational constraints. Finally, we present the $z=0$ power spectra of MBH and galaxies, as well as their bias with respect to the matter power spectrum. We find that MBHs with $M_{\rm BH}\geq 10^{8}\ M_{\odot}$ and galaxies with $M_{\star}\geq 10^{10.5}\ M_{\odot}$ serve as good tracers of large-scale structure.

Figures (23)

• Figure 2: The black hole mass function in ASTRID at $z=0$. The black solid curve includes all the BHs. The orange and yellow solid curves show the contribution from the BH population with $L_{\mathrm{bol}}\geq 10^{41}\,$erg/s and $f_{\rm Edd}\geq 0.01$, respectively. The blue solid and dashed lines show the observational constraints given by Shankar2009 and Ueda2014.
• Figure 3: Left: Relation between BH bolometric luminosity $L_{\rm bol}$ and BH mass $M_{\rm BH}$ at $z=0$ in ASTRID. The underlying background shows a two-dimensional distribution of $L_{\mathrm{bol}}-M_{\mathrm{BH}}$. The blue solid line gives the median AGN luminosity for each $M_{\rm BH}$ bin, and the shaded area is the 16-84 percentiles. The orange dotted/dot-dashed/dashed/solid lines mark the $10^{0}$/$10^{-1}$/$10^{-2}$/$10^{-3} \times L_{\rm Edd}$, respectively. Right: The relation between BH bolometric luminosity $L_{\rm bol}$ and the stellar mass of their host galaxies $M_{\star}$.
• Figure 4: The Eddington ratio distributions for BH population in ASTRID at $z=0$. We show the BH in three mass bins: BHs with mass $M_{\rm BH}\leq 10^{7}$$M_{\odot}$ (blue), $M_{\rm BH}=10^{7}-10^{9}$$M_{\odot}$ (yellow), and those with $M_{\rm BH} > 10^{9}$$M_{\odot}$ (red). The three distributions are normalized to the BH number in the corresponding mass bin. The vertical line marks $\chi_{\rm thr}$ (the Eddington threshold for the AGN kinetic feedback mode; see equation \ref{['equ:chi_thr']}) for $M_{\rm BH}=10^{9}\,h^{-1}$$M_{\odot}$. In both panels, we only include the central BH, i.e., the most massive BH, of each galaxy.
• Figure 5: AGN hard X-ray (2-10 keV) luminosity function in ASTRID at z=0.4 (left), z=0.2 (middle), and z=0 (right). The orange solid line presents the results based on the radiative efficiency $\eta=0.1$, and the orange dashed line corresponds to $\eta=0.2$. In each panel, the purple region shows the observational constraints compiled by Shen2020, and the blue region is the observation from Buchner2015.
• Figure 6: The correlation between MBHs and their host galaxies at $z=0$ in ASTRID. We include only the most massive BHs in each galaxy. The left panel shows the relation between the MBH mass $M_{\mathrm{BH}}$ and the galaxy stellar mass $M_{\mathrm{\star}}$, and the right panel presents the correlation between galaxy central MBH mass $M_{\mathrm{BH}}$ and stellar velocity dispersion $\sigma$. $M_{\star}$ and $\sigma$ are measured based using the stars within twice the stellar half-mass radius. In both frames, the background shows the two-dimensional distribution of galaxies in ASTRID, sharing the color bar on the right. The blue solid curve and the shaded area represent the median and the 16-84th percentiles of the overall population. To guide the eye, we show some empirical scaling relations from the literature. For $M_{\rm BH}-M_{\star}$, we plot the scaling relations from McConnell2013 (red shaded line), Kormendy2013 (purple dot-dashed line), Baron2019 (purple dotted line), the early type galaxy sample (orange solid line), and the local broad-lin AGN sample (red solid line) in Reines2015. For $M_{\rm BH}-\sigma$, we include the fitted scaling relation from Kormendy2013 (orange solid line), McConnell2013 (orange dashed line), Martin-Navarro2018 (red dot-dashed line), and Baron2019 (red dotted line). The gray dashed contours represent the KDE estimate of the individual observed BHs (combined from Reines2015Bentz2018Baron2019 for $M_{\rm BH}-M_{\star}$ and Greene2006Xiao2011Baron2019 for $M_{\rm BH}-\sigma$), enclosing 97.5% of the observational sample. They visualize the observational scatter for $M_{\rm BH}$ (not the dispersion between different fitted relations).