arXiv subjects

Andrew Benson

Publications and source records attributed to Andrew Benson.

At least 37 records · Page 2Linked to original sources

arXiv2026

Accelerated calibration of semi-analytic galaxy formation models

We present an accelerated calibration framework for semi-analytic galaxy formation models, demonstrated with Galacticus. Rather than fitting directly to properties such as the low-redshift stellar mass function (SMF) - which requires evolving thousands of halos per likelihood evaluation - we construct a fast likelihood from the stellar-to-halo mass relation (SHMR; mean and scatter) evaluated at a small set of target halo masses, reducing each evaluation to simulating only tens of galaxies. We sample the posterior over Galacticus parameters with Markov Chain Monte Carlo and show that the resulting calibration reproduces the low-redshift SMF. We then extend the method to additional datasets, using a higher-redshift SHMR and the low-redshift stellar mass-size relation as examples, and assess performance for large scale structure survey-relevant properties: stellar masses, sizes, and emission-line strengths. The SMF matches data well at low redshift, but toward higher redshift the model yields too few massive galaxies and too many low-mass galaxies. Size evolution with redshift is approximately correct, but the mass-size relation is too flat, producing massive galaxies that are too small. The H$α$ luminosity function is well reproduced at z~2, but by z~0.4 the model overproduces highly star-forming, H$α$-bright systems. These discrepancies suggest the model lacks sufficient flexibility (e.g. in gas cooling/recycling or feedback) to reconcile all datasets simultaneously. Our strategy complements emulator-based methods for calibrating semi-analytic models by enabling rapid, low-cost scans of model choices and parameterisations - a capability we envision leveraging to supply calibrated starting points for more detailed follow-up inference.

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arXiv2025

Bayesian Posteriors with Stellar Population Synthesis on GPUs

Models of Stellar Population Synthesis (SPS) provide a predictive framework for the spectral energy distribution (SED) of a galaxy. SPS predictions can be computationally intensive, creating a bottleneck for attempts to infer the physical properties of large populations of individual galaxies from their SEDs and photometry; these computational challenges are especially daunting for near-future cosmology surveys that will measure the photometry of billions of galaxies. In this paper, we explore a range of computational techniques aimed at accelerating SPS predictions of galaxy photometry using the JAX library to target GPUs. We study a particularly advantageous approximation to the calculation of galaxy photometry that speeds up the computation by a factor of 50 relative to the exact calculation. We introduce a novel technique for incorporating burstiness into models of galaxy star formation history that captures very short-timescale fluctuations with negligible increase in computation time. We study the performance of Hamiltonian Monte Carlo (HMC) algorithms in which individual chains are parallelized across independent GPU threads, finding that our pipeline can carry out Bayesian inference at a rate of approximately $1000$ galaxy posteriors per minute on a single GPU. Our results provide an update to standard benchmarks in the literature on the computational demands of SPS inference; our publicly available code enables previously-impractical Bayesian analyses of large galaxy samples, and includes several standalone modules that could be adopted to speedup existing SPS pipelines.

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arXiv2025

The abundance and properties of the lowest luminosity dwarf galaxies around the Milky Way: Insights from Semi-Analytic Models

We investigate the formation and observable properties of faint satellite galaxies (M$_\rm V > -3$) in Milky Way-like halos using the semi-analytic galaxy formation model Galacticus. The ability of the smallest dark matter halos to form stars depends sensitively on the balance between gas cooling and reionization heating. To quantify how this balance shapes the abundance and properties of the faintest galaxies, we compare two model variants: a fiducial model that includes molecular hydrogen (H$_2$) cooling and UV background radiation, and a No-H$_2$ model with atomic cooling only. Both models reproduce the structural properties of brighter Milky Way satellites, but they diverge at the lowest luminosities in the hyper-faint regime. The fiducial model predicts a substantially larger population of such systems that are on average hosted in halos with lower peak masses and quenched earlier. Many of these predicted systems lie below current observational thresholds but are within reach of next-generation deep imaging surveys. The predicted size-luminosity distributions of both models overlap with the region occupied by recently discovered "ambiguous" systems, whose classification as galaxies or star clusters remains uncertain. Specifically, we find that hyper-faint satellites have line-of-sight velocity dispersions of $σ_{\rm los} \sim 1-3$ km/s in the fiducial model, nearly an order of magnitude higher than expected for purely self-gravitating stellar systems of the same stellar mass. This distinction underscores the diagnostic power of precise kinematic measurements for determining whether ambiguous objects are dark matter dominated dwarf galaxies or star clusters, and highlights the importance of upcoming spectroscopic campaigns in resolving the nature of the faintest satellites.

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arXiv2025

Cosmology with voids from the Nancy Grace Roman Space Telescope

We provide an accurate forecast of the expected constraining power from the main void statistics -- the void size function and the void-galaxy cross-correlation function -- to be measured by the Roman reference High Latitude Spectroscopic Survey from the Nancy Grace Roman Space Telescope. Relying on a realistic galaxy mock lightcone, covering 2000 square degrees, we find more than $8\times 10^4 $ voids and explore their constraining power in the framework of three different cosmological models: $Λ$CDM, $w$CDM, and $w_0 w_{\rm a}$CDM. This work confirms the strong complementarity of different void statistics and showcases the constraining power to be expected from Roman voids thanks to the combination of its high tracer density and large observed volume.

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arXiv2025

The Effects of Linear Matter Power Spectrum Enhancement on Dark Matter Substructure

We present cosmological dark matter (DM)--only zoom-in simulations of a Milky Way analog originating from enhanced linear matter power spectra $P(k)$ relative to the standard cold, collisionless DM (CDM) cosmology. We consider a Gaussian power excess in $P(k)$ followed by a cutoff in select cases; this behavior could arise from early-Universe physics that alters the primordial matter power spectrum or DM physics in the radiation-dominated epoch. We find that enhanced initial conditions (ICs) lead to qualitative differences in substructure relative to CDM. In particular, the subhalo mass function (SHMF) resulting from ICs with both an enhancement and cutoff is amplified at high masses and suppressed at low masses, indicating that DM substructure is sensitive to features in $P(k)$. Critically, the amplitude and shape of the SHMF enhancement depend on the wavenumber of the $P(k)$ excess and the presence or absence of a cutoff on smaller scales. These alterations to the SHMF are mainly imprinted at infall rather than during tidal evolution. Additionally, subhalos are found systematically closer to the host center, and their concentrations are increased in scenarios with $P(k)$ enhancement. Our work thus reveals effects that must be captured to enable $P(k)$ reconstruction using DM substructure.

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arXiv2025

Clustering analysis of BOSS-CMASS galaxies with semi-analytical model for galaxy formation and halo occupation distribution

The spatial distribution of massive and luminous galaxies have provided important constraints on the fundamental cosmological parameters and physical processes governing galaxy formation. In this work, we construct and compare independent galaxy-halo connection models in the application of clustering measurement at non-linear scales of BOSS-CMASS galaxies. In particular, we adopt a halo occupation distribution (HOD) model with 11 parameters and a semi-analytical model (SAM) with 16 parameters to describe the galaxy two point correlation function. With an empirical parameterization for the velocity field to model the redshift space distortion effect and the emulator technique, we can explore the parameter space of both models. We find that the HOD model is able to recover the underlying velocity field of SAM with an accuracy of 3\%, and can be improved to 1\% when the analysis is restricted to scales above 1$h^{-1}$Mpc. The comparison is based on multiple samplings in the parameter space which can verify the convergence of the models. Then we perform constraints on the model parameters using clustering measurement of CMASS galaxies. Although limited by the emulator accuracy and the flexibility of the model, we find that the clustering measurement is capable of constraining a subset of the SAM parameters, especially for components sensitive to the star formation rate. This result leads us to anticipate that a joint analysis of both clustering and abundance measurements can significantly constrain the parameters of galaxy formation physics, which requires further investigation from both theoretical and observational aspects.

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arXiv2025

Till the core collapses: the evolution and properties of self-interacting dark matter subhalos

One of the hottest questions in the cosmology of self-interacting dark matter (SIDM) is whether scatterings can induce detectable core-collapse in halos by the present day. Because gravitational tides can accelerate core-collapse, the most promising targets to observe core-collapse are satellite galaxies and subhalo systems. However, simulating small subhalos is computationally intensive, especially when subhalos start to core-collapse. In this work, we present a hierarchical framework for simulating a population of SIDM subhalos, which reduces the computation time to linear order in the total number of subhalos. With this method, we simulate substructure lensing systems with multiple velocity-dependent SIDM models, and show how subhalo evolution depends on the SIDM model, subhalo mass and orbits. We find that an SIDM cross section of $\gtrsim 200$ cm$^2$/g at velocity scales relevant for subhalos' internal heat transfer is needed for a significant fraction of subhalos to core-collapse in a typical lens system at redshift $z=0.5$, and that core-collapse has unique observable features in lensing. We show quantitatively that core-collapse in subhalos is typically accelerated compared to field halos, except when the SIDM cross section is non-negligible ($\gtrsim \mathcal{O}(1)$ cm$^2$/g) at subhalos' orbital velocities, in which case evaporation by the host can delay core-collapse. This suggests that substructure lensing can be used to probe velocity-dependent SIDM models, especially if line-of-sight structures (field halos) can be distinguished from lens-plane subhalos. Intriguingly, we find that core-collapse in subhalos can explain the recently reported ultra-steep density profiles of substructures found by lensing with the \emph{Hubble Space Telescope}

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arXiv2025

Diversity and universality: evolution of dwarf galaxies with self-interacting dark matter

Dark matter halos with self-interacting dark matter (SIDM) experience a unique evolutionary phenomenon, in that their central regions eventually collapse to high density through the runaway gravothermal process after initially forming a large and low-density core. When coupled with orbital evolution, this is expected to naturally produce a large diversity in dark-matter halos' inner mass distribution, potentially explaining the diversity problem of dwarf galaxies. However, it remains unknown how the diversity in SIDM dark-matter halos propagates to the more easily observed luminous matter at the center of the halo, especially the stellar component. In this work, we use idealized N-body simulations with two species of particles (dark matter and stars) to study the response of the stellar properties of field and satellite dwarf galaxies to SIDM evolution and orbital effects on their halos. Galaxies' stellar components, including galaxy size, mass-to-light ratio, and stellar velocity dispersion, display a much larger scatter in SIDM than the standard cold dark matter (CDM) model. Importantly, we find signs of universality in the evolution pathways, or "tidal tracks", of SIDM dwarf satellites, which are physically interpretable and potentially parameterizable. This type of tidal-track model can be layered onto larger-scale, cosmological simulations to reconstruct the evolution of populations of SIDM dwarfs in cases where high-resolution simulations of galaxies are otherwise prohibitively expensive.

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arXiv2025

Novel Challenges in Tracking Self-Interacting Dark Matter Subhalos

Cosmological N-body simulations are among the primary tools for studying structure formation in the Universe. Analyses of these simulations critically depend on accurately identifying and tracking dark matter subhalos over time. In recent years, several new algorithms have been developed to improve the accuracy and consistency of subhalo tracking in cold dark matter simulations. These algorithms should be revisited in the context of new physics beyond gravity, which can modify the evolution and final properties of subhalo populations. In this work, we apply the particle-tracking-based subhalo finder Symfind to velocity-dependent self-interacting dark matter simulations with large cross section amplitudes to assess the performance of particle-tracking methods beyond the CDM paradigm. We find that the core-particle-tracking technique, which is key to the success of these algorithms in CDM, does not always yield accurate results in SIDM. The interplay between dark matter self-interactions and tidal stripping can cause the diffusion of core particles to larger radii, leading particle-tracking-based algorithms to prematurely lose track of SIDM subhalos. For massive core-expansion subhalos and core-collapse subhalos that experience close or repeated pericentric passages, a significant fraction of core particles can be lost, and particle-tracking-based finders such as Symfind offer no clear advantage over traditional methods that rely on identifying phase-space overdensities. On the other hand, for subhalos with large pericentric distances or fewer, more distant passages, Symfind tends to outperform. These differences depend sensitively on the cross section amplitude and turnover velocity of the underlying SIDM model. We therefore recommend a hybrid approach that leverages the strengths of both techniques to produce complete and robust catalogs of core-expansion and core-collapse SIDM subhalos.

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arXiv2025

Calibrating the SIDM Gravothermal Catastrophe with N-body Simulations

Self-interacting dark matter (SIDM) theories predict that dark matter halos experience core-collapse in late-stage evolution, a process where the halo's inner region rapidly increases in density and decreases in size. This process can be modeled by treating the dark matter as a gravothermal fluid, and solving the fluid equations to predict the density profile evolution. This model is incomplete without calibration to N-body simulations, through a constant factor $β$ included in the thermal conductivity for the long-mean-free-path limit. The value of $β$ employed in the gravothermal fluid formalism has varied between studies, with no clear universal value in the literature. In this work, we use the N-body code Arepo to conduct a series of isolated core-collapse simulations across a range of scattering cross-sections, halo concentrations, and halo masses to calibrate the heat transfer parameter $β$. We find that $β$ is independent of cross-section, halo concentration, and halo mass for velocity independent elastic scattering cross-sections. We present a model for an effective $β$ as a function of a dimensionless cross-section, to describe halo evolution in the long mean free path limit, and show that it accurately captures halo evolution as long as the cross section is not too large. This effective model facilitates comparisons between simulations and the gravothermal model, and enables fast predictions of the dark matter density profile at any given time without running N-body simulations.

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arXiv2025

A Semi-Analytic model for Effects of Fuzzy Dark Matter Granule Perturbations on Orbital Motion

In fuzzy dark matter scenarios, the quantum wave nature of ultralight axion-like particles generates stochastic density fluctuations inside dark matter halos. These fluctuations, known as granules, perturb the orbits of subhalos and other orbiting bodies. While previous studies have simulated these effects using N-body techniques or modeled them statistically using diffusion approximations, we propose an alternative framework based on representing the perturbations as a Fourier series with random coefficients, which can be applied to individual orbits, not just populations. We extend the model to finite-size subhalos, identifying a critical length scale below which subhalos behave as point-mass particles. In contrast, larger subhalos exhibit suppressed perturbations from granules due to their extended mass profiles. Using FDM-Simulator, we validate our finite-size model by isolating granule accelerations and confirming their statistical effects on subhalo dynamics.

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arXiv2025

Faster than SAM: An empirical model for the tidal evolution of dark matter substructure around strong gravitational lenses

Strong gravitational lenses enable direct inference of halo abundance and internal structure, which in turn enable constraints on the nature of dark matter and the primordial matter power spectrum. However, the density profiles of dark subhalos around the main deflector of a strong lens system also depend on tidal evolution inside the host, complicating the interpretation of strong-lensing inferences. We present a model for subhalo tidal evolution that accurately predicts the bound mass function and the density profiles of tidally stripped subhalos that appear near the Einstein radius of a typical deflector for a variety of dark matter models. This model matches predictions from the semianalytic model (SAM) {\sc galacticus}, but enables the simulation of subhalo populations in seconds, rather than hours. We use this model to examine the expected number of subhalos near the Einstein radius of a typical lens, and examine their lensing signals. We show that in cold dark matter the amplitude of the bound mass function is suppressed by a factor of $20$ relative to the infall mass function, and $87 \%$ of subhalos appearing in projection near the Einstein radius of a typical strong lensing deflector have lost more than $80\%$ of their mass since infall. Tidal stripping becomes increasingly severe in dark matter models with suppressed small-scale power, such as warm dark matter. This model will be used to forward model subhalo populations in forthcoming analyses of strong lens systems.

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arXiv2025

Generating Dark Matter Subhalo Populations Using Normalizing Flows

Strong gravitational lensing is a powerful tool for probing the nature of dark matter, as lensing signals are sensitive to the dark matter substructure within the lensing galaxy. We present a comparative analysis of strong gravitational lensing signatures generated by dark matter subhalo populations using two different approaches. The first approach models subhalos using an empirical model, while the second employs the Galacticus semi-analytic model of subhalo evolution. To date, only empirical approaches have been practical in the analysis of lensing systems, as incorporating fully physical models was computationally infeasible. To circumvent this, we utilize a generative machine learning algorithm, known as a normalizing flow, to learn and reproduce the subhalo populations generated by Galacticus. We demonstrate that the normalizing flow algorithm accurately reproduces the Galacticus subhalo distribution while significantly reducing computation time compared to direct simulation. Moreover, we find that subhalo populations from Galacticus produce comparable results to the empirical model in replicating observed lensing signals under the fiducial dark matter model. This work highlights the potential of machine learning techniques in accelerating astrophysical simulations and improving model comparisons of dark matter properties.

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arXiv2025

The THESAN project: environmental drivers of Local Group reionization

The timing of cosmic reionization across Local Group (LG) analogues provides insights into their early histories and surrounding large-scale structure. Using the radiation-hydrodynamic simulation THESAN-1 and its dark matter-only counterpart THESAN-DARK-1, we track the reionization histories of all haloes, including 224 LG analogues within the proximity of any of the 20 Virgo-like clusters with halo masses above 10^14 Msun at z=0 and their environments. The statistically controlled samples quantify how the reionization redshift (z_reion) correlates with halo mass, local overdensity, and present-day pair properties. Even at fixed mass, haloes in denser regions ionize earlier, and increasing the overdensity smoothing scale systematically suppresses small-scale structure, including local variations and environmental gradients in z_reion. Virgo-like clusters accelerate reionization in their surroundings out to ~5-10 cMpc, beyond which local overdensity again becomes the dominant factor. Within LG pairs, reionization timing offsets reach up to ~150 Myr and correlate with present-day halo separation, reflecting sensitivity to large-scale structure rather than mass ratio in driving asynchronous reionization. The results support an extreme inside-out picture where clustered sources rapidly ionize their immediate neighborhoods, while lower-density regions self-ionize later and voids wait for external homogenization. These links between environment and reionization timing explain the influence of protoclusters and help interpret fossil records in LG dwarfs around the Milky Way. For Milky Way analogues, we find a reionization redshift as early (late) as z_reion = 12.7^{+2.0}_{-1.7} (8.88^{+0.66}_{-0.70}) when considered on 125 ckpc (500 ckpc) scales, with LG analogues following an inside-out reionization picture.

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arXiv2025

COZMIC. III. Cosmological Zoom-in Simulations of Self-interacting Dark Matter with Suppressed Initial Conditions

We present eight cosmological dark matter (DM)--only zoom-in simulations of a Milky Way--like system that include suppression of the linear matter power spectrum $P(k)$, and/or velocity-dependent DM self-interactions, as the third installment of the COZMIC suite. We consider a model featuring a massive dark photon that mediates DM self-interactions and decays into massless dark fermions. The dark photon and dark fermions suppress linear matter perturbations, resulting in dark acoustic oscillations in $P(k)$, which ultimately affect dwarf galaxy scales. The model also features a velocity-dependent elastic self-interaction between DM particles (SIDM), with a cross section that can alleviate small-scale structure anomalies. For the first time, our simulations test the impact of $P(k)$ suppression on gravothermal evolution in an SIDM scenario that leads to core collapse in (sub)halos with present-day virial masses below $\approx 10^9~M_{\mathrm{\odot}}$. In simulations with $P(k)$ suppression and self-interactions, the lack of low-mass (sub)halos and the delayed growth of structure reduce the fraction of core-collapsed systems relative to SIDM simulations without $P(k)$ suppression. In particular, $P(k)$ suppression that saturates current warm DM constraints almost entirely erases core collapse in isolated halos. Models with less extreme $P(k)$ suppression produce core collapse in $\approx 20\%$ of subhalos and $\approx 5\%$ of isolated halos above $10^8~M_{\mathrm{\odot}}$, and also increase the abundance of extremely low-concentration isolated low-mass halos relative to SIDM. These results reveal a complex interplay between early and late-Universe DM physics, revealing new discovery scenarios in the context of upcoming small-scale structure measurements.

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arXiv2025

COZMIC. II. Cosmological Zoom-in Simulations with Fractional non-CDM Initial Conditions

We present $24$ cosmological dark matter (DM)-only zoom-in simulations of a Milky Way analog with initial conditions appropriate for scenarios where non-cold dark matter (NCDM) is a fraction of the total DM abundance (f-NCDM models) as the second installment of the COZMIC suite. We initialize our simulations using transfer functions, $T_{\mathrm{f-NCDM}}(k)\equiv\sqrt{P_{\mathrm{f-NCDM}}(k)/P_{\mathrm{CDM}}(k)}$ (where $P(k)$ is the linear matter power spectrum), with an initial suppression similar to thermal-relic warm dark matter (WDM) followed by a constant-amplitude plateau. We simulate suppression wavenumbers $[22.8,~ 32.1,~ 41.8,~ 52.0,~ 57.1,~ 95.3]~\mathrm{Mpc}^{-1}$, corresponding to thermal-relic WDM masses $m_{\mathrm{WDM}}\in [3,~ 4,~ 5,~ 6,~ 6.5,~ 10]~\mathrm{keV}$, and plateau amplitudes $δ\in [0.2,~ 0.4,~ 0.6,~ 0.8]$. We model the subhalo mass function in terms of the suppression wavenumber and $δ$. Integrating these models into a forward model of the MW satellite galaxy population yields new limits on f-NCDM scenarios, with suppression wavenumbers greater than $46$ and $ 40~\mathrm{Mpc}^{-1}$ for $δ=0.2$, $0.4$, respectively, at $95\%$ confidence. The current data do not constrain $δ>0.4$. We map these limits to scenarios where a fraction $f_{\mathrm{WDM}}$ of DM behaves as a thermal relic, which yields the following bounds on cosmologies with a mixture of WDM and CDM: $m_{\mathrm{WDM}}>3.6,~ 4.1,~ 4.6,~ 4.9,~ 5.4~\mathrm{keV}$ for $f_{\mathrm{WDM}}=0.5,~ 0.6,~ 0.7,~ 0.8,~ 0.9$, respectively, at $95\%$ confidence. The current data do not constrain WDM fractions $f_{\mathrm{WDM}}<0.5$. Our results affirm that low-mass halo abundances are sensitive to partial suppression in $P(k)$, indicating the possibility of using galactic substructure to reconstruct $P(k)$ on small scales.

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arXiv2025

COZMIC. I. Cosmological Zoom-in Simulations with Initial Conditions Beyond Cold Dark Matter

We present 72 cosmological dark matter-only $N$-body zoom-in simulations with initial conditions beyond cold, collisionless dark matter (CDM), as the first installment of the COZMIC suite. We simulate Milky Way (MW) analogs with linear matter power spectra $P(k)$ for i) thermal-relic warm dark matter (WDM) with masses $m_{\mathrm{WDM}}\in [3,4,5,6,6.5,10]~\mathrm{keV}$, ii) fuzzy dark matter (FDM) with masses $m_{\mathrm{FDM}}\in [25.9,69.4,113,151,185,490]\times 10^{-22}~\mathrm{eV}$, and iii) interacting dark matter (IDM) with a velocity-dependent elastic proton scattering cross section $σ=σ_0 v^n$ relative particle velocity scaling $n\in [2,4]$, and dark matter mass $m_{\mathrm{IDM}}\in[10^{-4},~ 10^{-2},~ 1]$ GeV. Subhalo mass function (SHMF) suppression is significantly steeper in FDM versus WDM, while dark acoustic oscillations in $P(k)$ can reduce SHMF suppression for IDM. We fit SHMF models to our simulation results and derive new bounds on WDM and FDM from the MW satellite population, obtaining $m_{\mathrm{WDM}}>5.9~\mathrm{keV}$ and $m_{\mathrm{FDM}}>1.4\times 10^{-20}~\mathrm{eV}$ at $95\%$ confidence; these limits are $\approx 10\%$ weaker and $5\times$ stronger than previous constraints owing to the updated transfer functions and SHMF models, respectively. We estimate IDM bounds for $n=2$ ($n=4$) and obtain $σ_0 < 1.0\times 10^{-27}$, $1.3\times 10^{-24}$, and $3.1\times 10^{-23}~\mathrm{cm}^2$ ($σ_0 < 9.9\times 10^{-27}$, $9.8\times 10^{-21}$, and $2.1\times 10^{-17}~\mathrm{cm}^2$) for $m_{\mathrm{IDM}}=10^{-4}$, $10^{-2}$, and $1$ GeV, respectively. Thus, future development of IDM SHMF models can improve IDM cross section bounds by up to a factor of $\sim 20$ with current data. COZMIC presents an important step toward accurate small-scale structure modeling in beyond-CDM cosmologies, critical to upcoming observational searches for dark matter physics.

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arXiv2025

A New Framework for ISM Emission Line Models: Connecting Multi-Scale Simulations Across Cosmological Volumes

The JWST and ALMA have detected emission lines from the ionized interstellar medium (ISM) in some of the first galaxies at $z \gtrsim 6$. These measurements present an opportunity to better understand galaxy assembly histories and may allow important tests of state-of-the-art galaxy formation simulations. It is challenging, however, to model these lines in their proper cosmological context. In order to meet this challenge, we introduce a novel sub-grid line emission modeling framework. The framework uses the high-$z$ zoom-in simulation suite from the Feedback in Realistic Environments (FIRE) collaboration. The line emission signals from HII regions within each simulated FIRE galaxy are modeled using the semi-analytic HIILines code. A machine learning approach is then used to determine the conditional probability distribution for the line luminosity to stellar-mass ratio from the HII regions around each simulated stellar particle. This conditional probability distribution can then be applied to predict the line luminosities around stellar particles in lower resolution, yet larger volume cosmological simulations. As an example, we apply this approach to the IllustrisTNG simulations at $z=6$. The resulting predictions for the [OII], [OIII], and Balmer line luminosities as a function of star-formation rate (SFR) agree well with current observations. Our predictions differ, however, from related work in the literature which lack detailed sub-grid ISM models. This highlights the importance of our multi-scale simulation modeling framework. Finally, we provide forecasts for future line luminosity function measurements from the JWST and quantify the cosmic variance in such surveys.

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