arXiv subjects

Adam Lidz

Publications and source records attributed to Adam Lidz.

At least 37 records · Page 2Linked to original sources

arXiv2025

LIMFAST. IV. Learning High-Redshift Galaxy Formation from Multiline Intensity Mapping with Implicit Likelihood Inference

By opening up new avenues to statistically constrain astrophysics and cosmology with large-scale structure observations, the line intensity mapping (LIM) technique calls for novel tools for efficient forward modeling and inference. Implicit likelihood inference (ILI) from semi-numerical simulations provides a powerful setup for investigating a large model parameter space in a data-driven manner, therefore gaining significant recent attention. Using simulations of high-redshift 158$μ$m [CII] and 88$μ$m [OIII] LIM signals created by the LIMFAST code, we develop an ILI framework in a case study of learning the physics of early galaxy formation from the auto-power spectra of these lines or their cross-correlation with galaxy surveys. We leverage neural density estimation with normalizing flows to learn the mapping between the simulated power spectra and parameters that characterize the physics governing the star formation efficiency and the $\dotΣ_{\star}$-$Σ_\mathrm{g}$ relation of high-redshift galaxies. Our results show that their partially degenerate effects can be unambiguously constrained when combining [CII] with [OIII] measurements to be made by new-generation mm/sub-mm LIM experiments.

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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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arXiv2025

Do cosmological simulations reproduce the [OIII] 88 $μ$m line emission and properties of JWST-discovered galaxies at $z \geq 12$?

Recent ALMA observations of the [OIII] 88 $μ$m line provide spectroscopic confirmation of two JWST photometric candidates, GS-z14 and GHZ2, at $z=14.2$ and $z=12.3$, respectively. These discoveries reveal that star formation and chemical enrichment were already underway when the universe was merely 300 Myr old, posing a challenge to galaxy formation models. Here we construct post-processed models for the [OIII] emission lines from galaxies in the state-of-the-art FIRE and IllustrisTNG simulations. Neither simulation suite contains galaxies directly comparable to GS-z14 or GHZ2. However, one simulated FIRE galaxy closely resembles GS-z14 in its star formation rate (SFR), stellar mass, metallicity, [OIII] luminosity and line-width, albeit at $z=8.7$, lagging GS-z14's formation by roughly 300 Myr. Although further investigation is required, we argue that the lack of simulated galaxies matching GS-z14 and GHZ2 may largely be a consequence of the limited volume of the FIRE simulations and the limited mass resolution of Illustris-TNG. We quantify the prospects for follow-up spectroscopic detections of GS-z14 in the [OIII] 52 $μ$m line with ALMA, and in rest-frame optical [OIII] and Balmer lines with the MIRI instrument on JWST.

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arXiv2025

Prospects for ${\rm kSZ^2}$-${\rm 21cm^2}$ Cross-Correlations during Reionization

The 21\,cm line and the patchy kinetic Sunyaev-Zel'dovich (kSZ) effect are promising and complementary probes of the Epoch of Reionization (EoR). A challenge for cross-correlating these two signals is that foreground avoidance or removal algorithms applied to the 21\,cm data inevitably sacrifice Fourier modes with long wavelengths along the line-of-sight (i.e., low-$k_\parallel$ modes), yet \textit{only} these same modes contribute to the kSZ signal. Here we show that a suitable kSZ$^2$ $\times$ 21\,cm$^2$ cross-correlation statistic nevertheless remains non-vanishing, even after filtering out the corrupted low-$k_\parallel$ Fourier modes from the 21\,cm data. We simulate the kSZ$^2$ $\times$ 21\,cm$^2$ cross-correlation signal across reionization-era redshifts and find distinctive redshift evolution. This signal peaks early in the reionization history, when the volume-averaged fraction is around $0.1 \lesssim x_\mathrm{HII} \lesssim 0.2$, after which it changes sign and reaches a minimum near reionization's midpoint ($x_\mathrm{HII} \sim 0.5$), while the signal gradually vanishes as reionization completes. These trends appear generic across three simulated models which differ in their reionization histories. We forecast the detectability of the kSZ$^2$ $\times$ 21\,cm$^2$ cross-power spectrum for the HERA and SKA1-Low 21\,cm experiments in combination with current and next-generation CMB surveys including the Simons Observatory, CMB-S4, and CMB-HD. We find that a high-significance detection ($\mathrm{S/N} \gtrsim 5σ$) is possible with SKA1-Low and CMB-S4.

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arXiv2025

Fuzzy Dark Matter Constraints from the Hubble Frontier Fields

In fuzzy dark matter (FDM) cosmologies, the dark matter consists of ultralight bosons ($m\lesssim10^{-20}$ eV). The astrophysically large de Broglie wavelengths of such particles hinder the formation of low-mass dark matter halos. This implies a testable prediction: a corresponding suppression in the faint-end of the ultraviolet luminosity function (UVLF) of galaxies. Notably, recent estimates of the faint-end UVLF at $z\sim5-9$ in the Hubble Frontier Fields, behind foreground lensing clusters, probe up to five magnitudes fainter than typical ("blank-field") regions. These measurements thus far disfavor prominent turnovers in the UVLF at low luminosity, implying bounds on FDM. We fit a semi-empirical model to these and blank-field UVLF data, including the FDM particle mass as a free parameter. This fit excludes cases where the dark matter is entirely a boson of mass $m<1.5\times10^{-21}$ eV (with $2σ$ confidence). We also present a less stringent bound deriving solely from the requirement that the total observed abundance of galaxies, integrated over all luminosities, must not exceed the total halo abundance in FDM. This more model-agnostic bound disfavors $m<5\times10^{-22}$ eV ($2σ$). We forecast that future UVLF measurements from JWST lensing fields may probe masses several times larger than these bounds, although we demonstrate this is subject to theoretical uncertainties in modeling the FDM halo mass function.

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arXiv2025

LIMFAST. III. Timing Cosmic Reionization with the 21 cm and Near-Infrared Backgrounds

The timeline of cosmic reionization remains uncertain despite sustained efforts to study how the ionizing output of early galaxies shaped the intergalactic medium (IGM). Using the semi-numerical code LIMFAST, we investigate the prospects for timing the reionization process by cross-correlating the 21 cm signal with the cosmic near-infrared background (NIRB) contributed by galaxies at $z>5$. Tracing opposite phases of the IGM on large scales during reionization, the two signals together serve as a powerful probe for the reionization history. However, because long-wavelength, line-of-sight Fourier modes -- the only modes probed by NIRB fluctuations -- are contaminated by 21 cm foregrounds and thus inevitably lost to foreground cleaning or avoidance, a direct cross-correlation of the two signals vanishes. We show that this problem can be circumvented by squaring the foreground-filtered 21 cm signal and cross-correlating the squared field with the NIRB. This statistic is related to the 21 cm--21 cm--NIRB cross-bispectrum and encodes valuable information regarding the reionization timeline. Particularly, the 21 cm$^2$ and NIRB signals are positively correlated during the early phases of reionization and negatively correlated at later stages. We demonstrate that this behavior is generic across several different reionization models and compare our simulated results with perturbative calculations. We show that this cross-correlation can be detected at high significance by forthcoming 21 cm and NIRB surveys such as SKA and SPHEREx. Our methodology is more broadly applicable to cross-correlations between line intensity mapping data and 2D tracers of the large-scale structure, including photometric galaxy surveys and CMB lensing mass maps, among others.

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arXiv2025

Signatures of high-redshift galactic outflows in the thermal Sunyaev Zel'dovich effect

Anisotropies of the Sunyaev Zel'dovich (SZ) effect serve as a powerful probe of the thermal history of the universe. At high redshift, hot galactic outflows driven by supernovae (SNe) can inject a significant amount of thermal energy into the intergalactic medium, causing a strong $y$-type distortion of the CMB spectrum through inverse Compton scattering. The resulting anisotropies of the $y$-type distortion are sensitive to key physical properties of high-$z$ galaxies pertaining to the launch of energetic SNe-driven outflows, such as the efficiency and the spatio-temporal clustering of star formation. We develop a simple analytic framework to calculate anisotropies of $y$-type distortion associated with SNe-powered outflows of galaxies at $z>6$. We show that galactic outflows are likely the dominant source of thermal energy injection, compared to contributions from reionized bubbles and gravitational heating. We further show that next-generation CMB experiments such as LiteBIRD are likely to detect the contribution to $y$ anisotropies from high-$z$ galactic outflows through the cross-correlation with surveys of Lyman-break galaxies by e.g. the Roman Space Telescope. Our analysis and forecasts demonstrate that thermal SZ anisotropies can be a promising probe of SN feedback and outflows in early star-forming galaxies.

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arXiv2024

Analytical strong line diagnostics and their redshift evolution

The \textit{JWST} is allowing new measurements of gas-phase metallicities in galaxies between cosmic noon and cosmic dawn. The most robust approach uses luminosity ratios between the excited auroral transition, [\oiii] 4364\,Å, and the lower [\oiii] 5008\,Å/4960\,Å lines to determine the gas temperature. The ratio of the luminosities in the latter transitions to those in hydrogen Balmer series lines then yield relatively clean metallicity estimates. In the absence of detection of the [\oiii] auroral line, the ratios of various [\oiii], [\oii], [\nii], and Balmer lines are used to determine metallicities. Here we present a refined approach for extracting metallicities from these ``strong line diagnostics''. Our method exploits empirical correlations between the temperature of \oiii/\oii\ regions and gas-phase metallicity. We then show, from first principles, how to extract metallicities and break degeneracies in these estimates using traditional strong line diagnostics, R2, R3, R23, and O3O2, and N2O2. We show that these ratios depend also on volume correction factors, i.e. on accounting for the fraction of the volume of HII regions that are in \oiii\ and \oii, but that these can be determined self-consistently along with the metallicities. We quantify the success of our method using metallicities derived from galaxies with auroral line determinations and show that it generally works better than previous empirical approaches. The scatter in the observed line ratios and redshift evolution are largely explained by O3O2 variations. We provide publicly available routines for extracting metallicities from strong line diagnostics using our methodology.

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arXiv2024

The relative constraining power of the high-$z$ 21-cm dipole and monopole signals

The 21-cm background is a promising probe of early star formation and black hole activity. While a slew of experiments on the ground seek to detect the 21-cm monopole and spatial fluctuations on large $\sim 10$ arcminute scales, little work has been done on the prospects for detecting the 21-cm dipole signal or its utility as a probe of early galaxies. Though an intrinsically weak signal relative to the monopole, its direction is known well from the cosmic microwave background and wide-field surveys, plus as a relative measurement the dipole could help relax instrumental requirements. In order to understand the constraining power of the dipole, in this work we perform parameter inference on mock datasets that include the dipole, monopole, or both signals. We find that while the monopole does provide the best constraints for a given integration time, constraints from a dipole measurement are competitive, and can in principle constrain the cosmic star formation rate density and efficiency of X-ray photon production in early $z \sim 15$ galaxies to better than a factor of $\sim 2$. This result holds for most of the available prior volume, which is set by constraints on galaxy luminosity functions, the reionization history, and upper limits from 21-cm power spectrum experiments. We also find that predictions for the monopole from a dipole measurement are robust to different choices of signal model. As a result, the 21-cm dipole signal is a valuable target for future observations and offers a robust cross-check on monopole measurements.

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arXiv2024

Insights into the 21 cm field from the vanishing cross-power spectrum at the epoch of reionization

The early stages of the Epoch of Reionization, probed by the 21 cm line, are sensitive to the detailed properties and formation histories of the first galaxies. We use 21cmFAST and a simple, self-consistent galaxy model to examine the redshift evolution of the large-scale cross-power spectrum between the 21 cm field and line-emitting galaxies. A key transition in redshift occurs when the 21 cm field shifts from being positively correlated with the galaxy distribution to being negatively correlated. Importantly, this transition redshift is insensitive to the properties of the galaxy tracers but depends sensitively on the thermal and ionization histories traced through the 21 cm field. Specifically, we show that the transition occurs when both ionization fluctuations dominate over 21 cm spin temperature fluctuations and when the average spin temperature exceeds the temperature of the cosmic microwave background. We illustrate this with three different 21 cm models which have largely the same neutral fraction evolution but different heating histories. We find that the transition redshift has a scale dependence, and that this can help disentangle the relative importance of heating and ionization fluctuations. The best prospects for constraining the transition redshift occur in scenarios with late X-ray heating, where the transition occurs at redshifts as low as $z \sim 6-8$. In our models, this requires high-redshift galaxy surveys with sensitivities of $\sim 10^{-18}~\rm erg/s/cm^2$ for optical lines and $\sim 10^{-19}~\rm erg/s/cm^2$ for FIR lines. Future measurements of the transition redshift can help discriminate between 21 cm models and will benefit from reduced systematics.

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arXiv2024

Is the Radio Source Dipole from NVSS Consistent with the CMB and $Λ$CDM?

The dipole moment in the angular distribution of the cosmic microwave background (CMB) is thought to originate from the Doppler effect and our motion relative to the CMB frame. Observations of large-scale structure (LSS) should show a related ``kinematic dipole'' and help test the kinematic origin of the CMB dipole. Intriguingly, many previous LSS dipole studies suggest discrepancies with the expectations from the CMB. Here we reassess the apparent inconsistency between the CMB measurements and dipole estimates from the NVSS catalog of radio sources. We find that it is important to account for the shot noise and clustering of the NVSS sources, as well as kinematic contributions, in determining the expected dipole signal. We use the clustering redshift method and a cross-matching technique to refine estimates of the clustering term. We then derive a probability distribution for the expected NVSS dipole in a standard $Λ$CDM cosmological model including all (i.e., kinematic, shot-noise and clustering) dipole components. Our model agrees with most of the previous NVSS dipole measurements in the literature at better than $\lesssim 2σ$. We conclude that the NVSS dipole is consistent with a kinematic origin for the CMB dipole within $Λ$CDM.

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arXiv2023

The Star Formation Efficiency During Reionization as Inferred from the Hubble Frontier Fields

A recent ultraviolet luminosity function (UVLF) analysis in the Hubble Frontier Fields, behind foreground lensing clusters, has helped solidify estimates of the faint-end of the $z \sim 5-9$ UVLF at up to five magnitudes fainter than in the field. These measurements provide valuable information regarding the role of low luminosity galaxies in reionizing the universe and can help in calibrating expectations for JWST observations. We fit a semi-empirical model to the lensed and previous UVLF data from Hubble. This fit constrains the average star formation efficiency (SFE) during reionization, with the lensed UVLF measurements probing halo mass scales as small as $M \sim 2 \times 10^9 {\rm M}_\odot$. The implied trend of SFE with halo mass is broadly consistent with an extrapolation from previous inferences at $M \gtrsim 10^{10} {\rm M}_\odot$, although the joint data prefer a shallower SFE. This preference, however, is partly subject to systematic uncertainties in the lensed measurements. Near $z \sim 6$ we find that the SFE peaks at $\sim 20 \%$ between $\sim 10^{11}-10^{12} {\rm M}_\odot$. Our best fit model is consistent with Planck 2018 determinations of the electron scattering optical depth, and most current reionization history measurements, provided the escape fraction of ionizing photons is $f_{\rm esc} \sim 10-20\%$. The joint UVLF accounts for nearly $80\%$ of the ionizing photon budget at $z \sim 8$. Finally, we show that recent JWST UVLF estimates at $z \gtrsim 11$ require strong departures from the redshift evolution suggested by the Hubble data.

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arXiv2023

Boosting Line Intensity Map Signal-to-Noise with the Ly-$α$ Forest Cross-Correlation

We forecast the prospects for cross-correlating future line intensity mapping (LIM) surveys with the current and future Ly-$α$ forest data. We use large cosmological hydrodynamic simulations to model the expected emission signal for the CO rotational transition in the COMAP LIM experiment at the 5-year benchmark and the Ly-$α$ forest absorption signal for various surveys, including eBOSS, DESI, and PFS. We show that CO$\times$Ly-$α$ forest can significantly enhance the detection signal-to-noise ratio of CO, with a $200$ to $300 \%$ improvement when cross-correlated with the forest observed in the Prime Focus Spectrograph (PFS) survey and a $50$ to $75\%$ enhancement for the currently available eBOSS or the upcoming DESI observations. We compare to the signal-to-noise improvements expected for a galaxy survey and show that CO$\times$Ly-$α$ is competitive with even a spectroscopic galaxy survey in raw signal-to-noise. Furthermore, our study suggests that the clustering of CO emission is tightly constrained by CO$\times$Ly-$α$ forest, due to the increased signal-to-noise ratio and the simplicity of Ly-$α$ absorption power spectrum modeling. Any foreground contamination or systematics are expected not to be shared between LIM surveys and Ly-$α$ forest observations; this provides an unbiased inference. Our findings highlight the potential benefits of utilizing the Ly-$α$ forest to aid in the initial detection of signals in line intensity experiments. For example, we also estimate that [CII]$\times$Ly-$α$ forest measurements from EXCLAIM and DESI/eBOSS, respectively, should have a larger signal-to-noise ratio than planned [CII]$\times$quasar observations by about an order of magnitude. Our results can be readily applied to actual data thanks to the observed quasar spectra in eBOSS Stripe 82, which overlaps with several LIM surveys.

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arXiv2023

Efficient simulations of ionized ISM emission lines: A detailed comparison between the FIRE high-redshift suite and observations

The Atacama Large Millimeter/Submillimeter Array (ALMA) in the sub-millimeter and the James Webb Space Telescope (JWST) in the infrared have achieved robust spectroscopic detections of emission lines from the interstellar medium (ISM) in some of the first galaxies. These unprecedented measurements provide valuable information regarding the ISM properties, stellar populations, galaxy morphologies, and kinematics in these high-redshift galaxies and, in principle, offer powerful tests of state-of-the-art galaxy formation models, as implemented in hydrodynamical simulations. To facilitate direct comparisons between simulations and observations, we develop a fast post-processing pipeline for predicting the line emission from the HII regions around simulated star particles, accounting for spatial variations in the surrounding gas density, metallicity, and incident radiation spectrum. Our ISM line emission model currently captures H$α$, H$β$, and all of the [OIII] and [OII] lines targeted by ALMA and the JWST at $z>6$. We illustrate the power of this approach by applying our line emission model to the publicly available Feedback In Realistic Environment (FIRE) high-$z$ simulation suite and perform a detailed comparison with current observations. We show that the FIRE mass--metallicity relation is in $1σ$ agreement with ALMA/JWST measurements after accounting for the inhomogeneities in ISM properties. We also quantitatively validate the one-zone model description, which is widely used for interpreting [OIII] and H$β$ line luminosity measurements. This model is publicly available and can be implemented on top of a broad range of galaxy formation simulations for comparison with JWST and ALMA measurements.

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arXiv2023

Probing bursty star formation by cross-correlating extragalactic background light and galaxy surveys

Understanding the star formation rate (SFR) variability and how it depends on physical properties of galaxies is important for developing and testing the theory of galaxy formation. We investigate how statistical measurements of the extragalactic background light (EBL) can shed light on this topic and complement traditional methods based on observations of individual galaxies. Using semi-empirical models of galaxy evolution and SFR indicators sensitive to different star formation timescales (e.g., H$α$ and UV continuum luminosities), we show that the SFR variability, quantified by the joint probability distribution of the SFR indicators (i.e., the bivariate conditional luminosity function), can be characterized as a function of galaxy mass and redshift through the cross-correlation between deep, near-infrared maps of the EBL and galaxy distributions. As an example, we consider combining upcoming SPHEREx maps of the EBL with galaxy samples from Rubin/LSST. We demonstrate that their cross-correlation over a sky fraction of $f_\mathrm{sky}\sim0.5$ can constrain the joint SFR indicator distribution at high significance up to $z\sim2.5$ for mass-complete samples of galaxies down to $M_{*}\sim10^9\,M_{\odot}$. These constraints not only allow models of different SFR variability to be distinguished, but also provide unique opportunities to investigate physical mechanisms that require large number statistics such as environmental effects. The cross-correlations investigated illustrate the power of combining cosmological surveys to extract information inaccessible from each data set alone, while the large galaxy populations probed capture ensemble-averaged properties beyond the reach of targeted observations towards individual galaxies.

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arXiv2023

Prospects for 21cm-Galaxy Cross-Correlations with HERA and the Roman High-Latitude Survey

The cross-correlation between the 21 cm field and the galaxy distribution is a potential probe of the Epoch of Reionization (EoR). The 21 cm signal traces neutral gas in the intergalactic medium and, on large spatial scales, this should be anti-correlated with the high-redshift galaxy distribution which partly sources and tracks the ionized gas. In the near future, interferometers such as the Hydrogen Epoch of Reionization Array (HERA) are projected to provide extremely sensitive measurements of the 21 cm power spectrum. At the same time, the Nancy Grace Roman Space Telescope (Roman) will produce the most extensive catalog to date of bright galaxies from the EoR. Using semi-numeric simulations of reionization, we explore the prospects for measuring the cross-power spectrum between the 21 cm and galaxy fields during the EoR. We forecast a 14$σ$ detection between HERA and Roman, assuming an overlapping survey area of 500 deg$^2$, redshift uncertainties of $σ_z = 0.01$ (as expected for the high-latitude spectroscopic survey of Ly$α$-emitting galaxies), and an effective Ly$α$ emitter duty cycle of $f_\mathrm{LAE} = 0.1$. Thus the HERA-Roman cross-power spectrum may be used to help verify 21 cm detections from HERA. We find that the shot-noise in the galaxy distribution is a limiting factor for detection, and so supplemental observations using Roman should prioritize deeper observations, rather than covering a wider field of view.

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arXiv2022

Intensity mapping from the sky: synergizing the joint potential of [OIII] and [CII] surveys at reionization

We forecast the ability of future-generation experiments to detect the fine-structure lines of the carbon and oxygen ions, [CII] and [OIII] in intensity mapping (IM) from the Epoch of Reionization ($z \sim 6-8$). Combining the latest empirically derived constraints relating the luminosity of the [OIII] line to the ambient star-formation rate, and using them in conjunction with previously derived estimates for the abundance of [CII] in haloes, we predict the expected auto-correlation IM signal to be observed using new experiments based on the Fred Young Submillimetre Telescope (FYST) and the balloon-borne facility, Experiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) over $z \sim 5.3 - 7$. We describe how improvements to both the ground-based and balloon-based surveys in the future will enable a cross-correlation signal to be detected at $\sim$ 10-30 $σ$ over $z \sim 5.3 - 7$. Finally, we propose a space-based mission targeting the [OIII] 88 and 52 $μ$m lines along with the [CII] 158 $μ$m line, configured to enhance the signal-to-noise ratio of cross-correlation measurements. We find that such a configuration can achieve a high-significance detection (hundreds of $σ$) in both auto- and cross-correlation modes.

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arXiv2022

Prospects for kSZ$^2$-Galaxy Cross-Correlations during Reionization

We explore a new approach for extracting reionization-era contributions to the kinetic Sunyaev-Zel'dovich (kSZ) effect. Our method utilizes the cross-power spectrum between filtered and squared maps of the cosmic microwave background (CMB) and photometric galaxy surveys during the Epoch of Reionization (EoR). This kSZ$^2$-galaxy cross-power spectrum statistic has been successfully detected at lower redshifts ($z \lesssim 1.5$). Here we extend this method to $z \gtrsim 6$ as a potential means to extract signatures of patchy reionization. We model the expected signal across multiple photometric redshift bins using semi-numeric simulations of the reionization process. In principle, the cross-correlation statistic robustly extracts reionization-era contributions to the kSZ signal, while its redshift evolution yields valuable information regarding the timing of reionization. Specifically, the model cross-correlation signal near $\ell \sim 1,000$ peaks during the early stages of the EoR, when about 20% of the volume of the universe is ionized. Detectible $\ell$ modes mainly reflect squeezed triangle configurations of the related bispectrum, quantifying correlations between the galaxy overdensity field on large scales and the smaller-scale kSZ power. We forecast the prospects for detecting this signal using future wide-field samples of Lyman-break galaxies from the Roman Space Telescope and next-generation CMB surveys including the Simons Observatory, CMB-S4, and CMB-HD. We find that a roughly 13$σ$ detection is possible for CMB-HD and Roman after summing over all $\ell$ modes. We discuss the possibilities for improving this approach and related statistics, with the aim of moving beyond simple detections to measure the scale and redshift dependence of the cross-correlation signals.

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