Theoretical Astrophysicist · Carnegie Observatories

Andrew Benson

I am a Staff Scientist at the Carnegie Observatories. My research is focused on understanding the nature of dark matter and the process of galaxy formation — combining analytic models, numerical simulations, and large astronomical surveys.

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Research focus

What I work on

Three threads tie my research together: building a coherent theoretical model of galaxy formation; constraining the microphysics of dark matter; and designing the synthetic universes that next-generation surveys need to interpret their data.

Galaxy formation

The Galacticus model

An open-source semi-analytic model of galaxy formation used to interpret observations across cosmic time.

Dark matter

Constraining dark matter microphysics

Using halo substructure, gravitational lensing, and dwarf galaxies to test warm, self-interacting, and other non-CDM models.

Surveys

Synthetic skies for next-gen surveys

Building galaxy mocks for the Roman GRS Project Infrastructure Team and the NASA Open Universe initiative.

Recent work

Selected recent papers

These cards are rebuilt automatically from my NASA ADS library on a weekly schedule. Summaries and figures are generated from the paper itself.

The Astrophysical Journal Supplement Series 2026

A Graph-based Neural-network Surrogate Model for an Accelerating Semianalytical Model of Galaxy Formation and Evolution

Li, Xuejie, A. Benson, et al.

A neural network that works directly on the branching histories of dark matter halos reproduces the galaxy properties predicted by a full semi-analytic model — stellar mass, luminosity, rotation, gas metal content, and star formation rate — over the first twelve billion years of cosmic time, matching stellar masses to within 0.19 to 0.28 dex. A single such surrogate holds up across different model parameter choices and halo histories, offering a fast stand-in when exploring the parameter space of galaxy formation models.

ADS · arXiv · DOI

arXiv e-prints 2026

Hot off the Stacks: X-rays in Romulus25, Part I - Comparisons to Observations from eRosita

Sanchez, N. Nicole, A. Benson, et al.

Galaxies in the Romulus25 simulation are surrounded by hot gas that shines too brightly in X-rays compared with eROSITA all-sky survey measurements, especially close to each galaxy, although the match is reasonable at the mass of the Milky Way. Treating the gas as free of heavy elements, in keeping with the simulation's lack of cooling by those elements, cuts the X-ray output nearly tenfold and brings it closer to the observations.

ADS · arXiv · DOI

arXiv e-prints 2026

Extra! Extra! X-ray Emission!: X-rays in Romulus25, Part II - Physical Drivers of X-ray Emission in the CGM

Sanchez, N. Nicole, A. Benson, et al.

The amount of hot gas around Milky Way-mass galaxies in the Romulus25 simulation is set by the combined energy released by stars and by central black holes, while the temperature and heavy-element content of that gas determine how brightly it shines in X-rays. Gas rich in heavy elements appears brighter for the same mass, which means X-ray observations of Milky Way-mass galaxies may be biased toward such halos.

ADS · arXiv · DOI

arXiv e-prints 2026

The SIRMOS mission concept: a space-based near-IR spectroscopic survey of 100 million galaxies in the Euclid Wide Survey footprint

Wirth, Gregory D., A. Benson, et al.

A proposed NASA space telescope called SIRMOS could record spectra of about 100 million distant galaxies in three years, using images from the Euclid mission to pick targets and an array of tiny movable mirrors to observe up to 4,000 at once. The resulting map of cosmic structure is designed to test how inflation seeded today's large-scale structure, reveal what drives the accelerating expansion of the universe, and precisely measure the combined mass of neutrinos.

ADS · arXiv · DOI

Astrophysics Source Code Library 2026

DiffstarPop: Population modeling of galaxy star-formation histories

Alarcon, Alex, A. Benson, et al.

A software package called DiffstarPop generates realistic populations of galaxy star-formation histories from the growth histories of their dark matter halos, including the chance that each galaxy has stopped forming stars. Galaxies at the centers of halos and satellites orbiting within them are treated separately, and ready-made settings are provided to match the IllustrisTNG, Galacticus, and UniverseMachine models.

ADS

The Open Journal of Astrophysics 2026

The Curious Case of Centaurus A: On the Subject of the Quenched satellites

Weerasooriya, Sachi, A. Benson, et al.

Models calibrated to the Milky Way overpredict the number of bright satellite galaxies within 150 kpc of Centaurus A by a factor of four, and chance alone cannot account for the shortfall. The missing satellites occupy the same region as Centaurus A's kiloparsec-scale radio lobes, and heating driven by the host's central black hole can suppress star formation in them enough to explain the deficit.

ADS · arXiv · DOI

See all recent papers →

Open source

Galacticus

Most of my modeling work happens inside Galacticus, an open-source semi-analytic model of galaxy formation that I wrote and continue to develop. It's used by groups around the world to study dark matter, galaxy evolution, and forecast observations for upcoming surveys. See the full software stack →