Sergio Martin-Alvarez
Kavli Institute for Particle Astrophysics and Cosmology
KIPAC - Stanford University
Azahar Simulations
Towards physically complete models of galaxy formation to explain observations of galaxies across cosmic time
Azahar is a new series of high-resolution cosmological simulations devoted to capturing both a large population of galaxies and the detail of their internal structures. Our main goal is to determine whether incorporating the physics that we know are important for galaxy formation can provide a replacement to the calibration of sub-grid prescriptions to reproduce galaxy properties and scaling relations.
The Azahar suite, exploring different physics in each of their combinations, is intended to isolate the effects and interplay of different physical processes. The physical completeness of the models also enables a more direct connection to observations through state-of-the-art forward modelling methods, to answer new and old questions of galaxy formation, and in preparation for upcoming multi-wavelength surveys.
Azahar at a glance
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New physics in the box: Azahar brings magnetohydrodynamics, on-the-fly radiative transfer, and cosmic rays into cosmological galaxy formation. These physics are often omitted or approximated in cosmological simulations, but are fundamental in shaping how galaxies regulate crucial properties such as star formation, winds, and enrichment.
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A High-resolution cosmological sub-volume: A cosmological box of 25 cMpc with a central region (~10×8×8 cMpc³) resolved down to ~20 physical parsec (full-cell size). In each run, the same physics is applied uniformly across this volume, forming thousands of galaxies per simulated model, to test whether different galaxy formation physics hold for a full population across cosmic time.
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Pandora heritage: Builds on the Pandora pathfinder project (Martin-Alvarez et al. 2023), which demonstrated how including these non-thermal processes in combination and self-consistently restructures dwarf galaxy formation.
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Science for JWST and beyond: Our early results are being used to interpret the properties of the first galaxies revealed by JWST, and to prepare for multi-wavelength, spatially resolved diagnostics from the next generation of telescopes (e.g. ngVLA, ELTs).
Visualization 1: zoomed-in views of one of the Azahar large galaxies, forming with standard hydrodynamics (top left), calibrated hydrodynamics (top right), radiative transfer (bottom left) and 'full-physics' (bottom right; radiative transfer, magnetism and cosmic rays).
Science Goals and Themes
Azahar is built around a simple idea: for galaxy formation models to be genuinely predictive, they need to not only reproduce the observables we find in galaxies around us, but do so by generating galaxies evolved by realistic physical processes. With this design logic at its core, below you can find some of the main scientific areas that motivate the simulation suite. These span from the study and understanding of the first galaxies, to the baryon cycle, the growth of black holes, and revealing the physics behind multi-wavelength observables.
Connecting high-redshift and late-time galaxy formation
Azahar asks whether the same physical framework can explain both the first galaxies seen by JWST and the more settled populations observed later in cosmic history, connecting rapid early growth with longer-term galaxy evolution in one coherent picture.
From the first black holes to galaxy quenching
The next stage of Azahar expands toward supermassive black holes and active galactic nuclei. A central question is whether non-thermal physics can connect rapid black hole growth in the early Universe with the later shutdown of star formation in massive galaxies.
Realistic galaxies without parameter calibration
Azahar tests whether a more complete physical model can recover galaxy populations and scaling relations without relying on calibration. This includes observables such as the UV luminosity function, galaxy sizes, metallicities, and star formation rates.
Connecting with detailed high-redshift observations
Azahar is designed to connect the physical evolution of the first galaxies to the increasingly detailed high-redshift observations from JWST, and those upcoming from the ELTs - detailed galaxy views of SEDs, emission lines, burstiness indicators, and more.
Bursty and steady star formation
Galaxies do not form stars at a constant pace. Azahar explores what sets the balance between bursty and steady growth, and how magnetism, radiation, cosmic rays, and turbulence shape star formation across scales.
Predictions for multi-wavelength galaxy observations
Azahar supports forward modelling across the spectrum, with predictions for multi-wavelength observations from ALMA, PRIMA, SKA/ngVLA, and other facilities. Comparing per-model predictions will test which physical processes drive which observed signatures.
How do galaxies shape the gas inside and around them?
Azahar follows how galaxies exchange gas, metals, energy, and magnetic fields with their surroundings. This helps reveal how winds are launched, how material is recycled, and how the baryon cycle appears in observations.
Galaxies Showcase
Visualization 2: large-scale view showing the inner region of the Azahar zoom. Colours show the cosmic rays (green) and magnetic fields (purple) in one of the 'full-physics' simulations.
Table 1: Suite of simulated models. Columns indicate from left to right the unique symbol and label to identify each simulation, whether the simulation models magnetic fields, whether the model includes on-the-fly radiative transfer, whether it includes cosmic rays, the stellar feedback configuration, and a short set of further details for each simulation. From top to bottom, each run increases in complexity by including additional physics and components.
Table 2: Summary of the simulation suite main physical and numerical parameters.
Publications with Azahar
Main Series:
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Martin-Alvarez et al. in prep.
Azahar suite introduction and first results.
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Park, Martin-Alvarez, & Wechsler. Submitted
Non-thermal Physics Drives Compact, Self-Regulated Galaxy Morphologies at Cosmic Dawn.
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Martin-Alvarez, Wechsler, & Sijacki. Submitted soon
Non-thermal physics drives star formation burstiness and luminosities of the first galaxies.
Precursor Studies:
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Belfiori, Martin-Alvarez, Lopez-Rodriguez, et al. (2025)
On the universality of the relation between magnetic fields and star formation in galaxies.
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Callum, Laporte, Martin-Alvarez, et al. (2024)
Deciphering Lyman-α emission deep into the epoch of reionization.
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Dome, Martin-Alvarez, Tacchella, et al. (2024)
Increased burstiness at high-z in multiphysics models combining SN feedback, RT, and CRs.
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Yuan, Martin-Alvarez, Haehnelt, et al. (2024)
Extended red wings and the visibility of reionization-epoch Lyman-α emitters.