A suite of cosmological zoom-in simulations that resolves the circumgalactic medium of Milky Way-like galaxies down to 200 pc — using fixed-volume mesh refinement in Arepo together with the IllustrisTNG feedback model. The full snapshot and catalog data are now public via Globus.
The circumgalactic medium (CGM) — the diffuse gas reservoir surrounding a galaxy — regulates how galaxies accrete fuel, recycle their winds, and ultimately form stars. But it is notoriously difficult to simulate: it fills an enormous volume at very low density, is intrinsically multiphase, and is stirred by chaotic environmental effects.
Standard cosmological simulations use mass-based refinement, which pours computational power into dense, star-forming regions and leaves the low-density CGM poorly resolved. ENGAWA takes the complementary path: a fixed-volume refinement criterion that caps the physical size of gas cells throughout the CGM, layered on top of the usual mass refinement. This is only practical with Arepo's hybrid, moving Voronoi mesh, where individual gas cells can be refined and de-refined on the fly.
The result is a consistent 200 pc spatial resolution maintained from the disk through the inner CGM out to 100 kpc — higher resolution, and extended over a larger region, than any previous work — combined with the well-studied IllustrisTNG stellar and AGN feedback model. Stellar radiation is then added in post-processing with the COLT radiative-transfer code for realistic ion populations.
The suite comprises four Milky Way-mass halos — two drawn from the Auriga project and two TNG50 subhalos — each re-simulated with the fixed-volume refinement scheme. Because the resolution levels are chosen so the interstellar medium stays essentially unchanged, the galaxies themselves are consistent between runs (stellar masses agree to within 4% at z = 0).
| Galaxy | Origin | M★ (1010 M☉) | M200 (1012 M☉) | R200 (kpc) | Max resolution |
|---|---|---|---|---|---|
| Au6 | Auriga halo 6 | 4.8 | 1.04 | 214 | 200 pc |
| Au8 | Auriga halo 8 | 3.0 | 1.08 | 216 | 500 pc |
| TNG-A (537941) | TNG50 subhalo | 5.2 | 1.02 | 212 | 200 pc |
| TNG-B (519311) | TNG50 subhalo | 9.2 | 1.39 | 236 | 500 pc |
Each galaxy is run with the default mass-based scheme plus up to three fixed-volume levels. The target cell volume Vtarget is applied within a comoving radius Rri = 100 ckpc and tapers to the default scheme by Rro = 200 ckpc; inside 0.15 R200 the disk/ISM stays at the fiducial TNG50-1 resolution.
| Run | Refinement | Vtarget (kpc3) | Spatial resolution |
|---|---|---|---|
| Default | Mass-based only | — | TNG50-1 fiducial |
| 1 kpc | + fixed volume | 1.0 | 1 kpc |
| 500 pc | + fixed volume | 0.125 | 500 pc |
| 200 pc | + fixed volume | 0.015 | 200 pc (Au6, TNG-A) |
H I and Mg II column densities rise by ~4 orders of magnitude as resolution increases, bringing them into agreement with COS-Halos observations. Higher resolution produces many more small, cool clouds.
Total gas and O VI columns barely change with resolution, but the O VI-bearing gas becomes far more filamentary and structured. As in prior work, O VI still undercuts observations by a factor of a few.
Adding stellar ionizing radiation with COLT reduces H I toward observed values, while Mg II and O VI are largely unaffected — tempering the pure-resolution effect while staying consistent with data.
Stellar masses, gas masses, and star-formation rates are essentially unchanged by the added refinement — the extra resolution reshapes the CGM without perturbing the galaxy it surrounds.
The number of small cold clouds keeps growing with resolution while the count of large clouds converges. Their mass–size relation follows the local Larson relation with a slope of ~2.2.
The warm intermediate-temperature boundary layers around small clouds shrink at higher resolution, giving sharper, more rapid transitions to the ambient CGM temperature.
The ENGAWA data are hosted on a Globus collection. Globus is the standard tool for moving large scientific datasets: it manages reliable, resumable, high-throughput transfers between endpoints so you don't have to babysit multi-terabyte downloads. Access is free with any institutional or Globus ID login.
Follow the file-manager link and log in with your institutional identity or a free Globus ID. You'll land at the root of the ENGAWA collection.
In the second Globus pane, select where the files should go: your institution's managed endpoint, or your own laptop/desktop after installing Globus Connect Personal.
Select the galaxies/snapshots you need and hit Start. Globus handles retries and integrity checks; you'll be emailed when it completes. Individual small files can also be pulled straight over HTTPS from the web view.
With the Globus CLI (pip install globus-cli):
# authenticate once globus login # set the ENGAWA collection as a shell variable EP=a4a95e3b-cd86-4a58-acf2-d68291249997 # browse the tree globus ls $EP:/ globus ls $EP:/Au6/200pc/ # recursive transfer to your endpoint (DEST_EP) globus transfer $EP:/Au6/ DEST_EP:/data/engawa/Au6/ \ --recursive --label "ENGAWA Au6"
Replace DEST_EP with your own endpoint UUID (globus endpoint search to find it). Adjust the source paths to match the layout shown at right.
If you use these simulations, please cite the ENGAWA paper. Please also acknowledge the Auriga and IllustrisTNG projects, whose initial conditions and feedback model this suite builds on.
@article{Lucchini2026_ENGAWA,
author = {Lucchini, S. and Abramson, C. and Hummels, C. and
Conroy, C. and Hernquist, L. and Smith, A.},
title = {{ENhanced Galactic Atmospheres With Arepo:
Resolving the CGM at 200 pc with the ENGAWA Simulations}},
journal = {submitted to ApJ},
year = {2026},
eprint = {2603.05584},
archivePrefix = {arXiv}
}