Introducing NewCluster: the first half of the history of a high-resolution cluster simulation

TL;DR

NewCluster addresses the need for a high-resolution cosmological cluster simulation by targeting a $4.1\sigma$ overdensity region that will form a Virgo-like cluster with $M_{200}\approx 5\times10^{14}\,M_\odot$, extending to $3.5\,R_{\rm vir}$.It employs RAMSES-yOMP with adaptive mesh refinement to achieve a physical resolution of $68\,\mathrm{pc}$ and a stellar particle mass of $2\times10^{4}\,M_\odot$, with $15\,\mathrm{Myr}$ cadence snapshots and on-the-fly dust and ten-element chemical evolution, complemented by Monte Carlo gas tracers.The study presents detailed results up to $z=0.8$, including a major merger with mass ratio $\sim 1:3.2$, ram-pressure stripping of satellites, emergence of low-surface-brightness structures, and robust galaxy scaling relations that reveal environmental effects within the forming cluster.By providing public data products and leveraging high-resolution insights into MBH feedback, dust physics, and gas dynamics, NewCluster demonstrates both the scientific potential and computational challenges of modeling cluster environments at sub-kiloparsec scales, while outlining a path toward expanding to multiple clusters.

Abstract

We introduce NewCluster, a new high-resolution cluster simulation designed to serve as the massive halo counterpart of the modern cosmological galaxy evolution framework. The zoom-in simulation targets a volume of $4.1σ$ overdensity region, which is expected to evolve into a galaxy cluster with a virial mass of $5 \times 10^{14} M_\odot$, comparable to that of the Virgo Cluster. The zoom-in volume extends out to 3.5 virial radii from the central halo. The novelties of NewCluster are found in its resolutions. Its stellar mass resolution of $2 \times 10^{4} M_\odot$ is effective for tracing the early assembly of massive galaxies as well as the formation of dwarf galaxies. The spatial resolution of 68 parsecs in the best-resolved regions in the adaptive-mesh-refinement approach is powerful to study the detailed kinematic structure of galaxies. The time interval between snapshots is also exceptionally short-15 Myr-which is ideal for monitoring changes in the physical properties of galaxies, particularly during their orbital motion within a larger halo. The simulation has up-to-date feedback schemes for supernovae and active galactic nuclei. The chemical evolution is calculated for ten elements, along with dust calculation that includes the formation, size change, and destruction. To overcome the limitations of the Eulerian approach used for gas dynamics in this study, we employ Monte Carlo-based tracer particles in NewCluster, enabling a wide range of scientific investigations.

Figures (12)

• Figure 1: Overview of the NewCluster simulation. The figure shows images of (a) the large-scale volume that includes a low-resolution region, (b) the zoom-in region that includes clusters and local gas filaments, (c) the main cluster and infalling galaxies, and (d) the central brightest cluster galaxy with a relatively massive companion on the lower right side. Each panel shows a different combination of components that are specified on the upper left side with their corresponding colours. The extent of zoom-in panels (b), (c), and (d) is indicated by thin green boxes in larger panels (a), (b), and (c), respectively. Panels (e), (f), (g), and (h) show the region around the same target halo at different redshifts, $z=1.0$, $1.5$, $2.5$, and $4.0$. The scale bar indicates physical lengths in all panels.
• Figure 2: A sample of mock images of galaxies at three different redshifts ($z = 1.50$, $1.15$, and $0.80$) is shown. The SDSS $g$-, $r$-, and $i$-band fluxes (mapped to blue, green, and red, respectively) are used to construct the colour images. Based on stellar population and dust information, NewCluster successfully reproduces a wide variety of galaxy types.
• Figure 3: The scaling relations of NewCluster galaxies measured at $z=0.8, 1.5, 2.5$, and $4.0$. The $x$-axis shows the stellar mass, and the $y$-axis in each panel indicates different scaling properties for galaxies. The pixels on the background represent the distribution of NewCluster galaxies at $z=0.8$. Panel (a) presents the star formation rate of galaxies, which shows an overall decrease with redshift. Panel (b) presents the cold gas fraction of galaxies, which shows no strong evolution with redshift. However, the embedded figure in the panel, which presents the fraction of cold gas-deficient galaxies, shows an increase with redshift, particularly among lower-mass galaxies. Panel (c) presents half mass radius, which shows an increase over time over the entire mass range. Significant size growth is observed in high-mass galaxies, driven by mergers followed by wet compaction events. Panel (d) presents stellar metallicity, which exhibits a tight relation consistent with the empirical trend and shows no strong evolution with redshift. Panel (e) presents rotation velocity over velocity dispersion. Massive galaxies initially preferentially develop a strong rotation-supported system, which can be considered as disc settling, but experience a significant decrease in their rotation speed over time, indicating the formation of a slow rotator population through mergers. Panel (f) presents the mass of the most massive black holes in galaxies. The scaling relation lies well between the empirical relation of broad-line AGNs (solid line) and elliptical galaxies (dashed line).
• Figure 4: Stellar-to-halo mass ratio as a function of halo mass for all central galaxies. Circles show median values in each bin, colour-coded with different redshifts. Shade indicates $1\sigma$ scatter of the distribution at $z=0.8$. Stars indicate individual galaxies. Empirical relations at $z=0.8$ are shown as black lines.
• Figure 5: Photometric properties of NewCluster galaxies at $z=0.8$. The $x$-axis shows the $r$-band absolute magnitude. The $y$-axis of the top (bottom) panel represents $g-r$ colour ($g$-band effective surface brightness). We also present the black arrow to show the effect of dust attenuation assuming $\rm E(B-V)=0.1$ with Calzetti attenuation curve Calzetti2000. The colour of data points indicates the mass-weighted age of galaxies. The grey contours in both panels represent local observations from SDSS Nair2010.