Line intensity mapping (LIM) is a technique for producing three-dimensional maps of the Universe by scanning the sky with a spectrometer sensitive to a range of wavelengths corresponding to the redshifted spectral lines of atoms or molecules, such as hydrogen or carbon, commonly found in galaxies and the diffuse media around them. While LIM experiments have successfully detected the 21 cm line of neutral hydrogen, other lines that reveal large-scale structure or astrophysical processes remain undetected. Many LIM experiments are in development or are underway to fill this gap, but will likely suffer from contamination from systematics, like Galactic foregrounds, or noise. Cross-correlation techniques offer the smoothest route for making detections and constraining astrophysical processes in this regime. In this work, we apply three cross-correlation techniques [stacking, the conditional voxel intensity distribution, and the cross-power spectrum] to simulated LIM maps produced using [C ii] luminosity models for a pathfinder LIM experiment (EXCLAIM). We find that these cross-correlation techniques allow for mean detection of the target signal line ([C ii]) at redshifts 2.5-3.5 at the 3.9$\sigma$, 3.7$\sigma$, and 4.2$\sigma$ level, respectively, and offer moderate constraints on the line emission model. Under a futuristic scenario with reduced noise, the techniques improve substantially, with detections at the 35.4$\sigma$, 76.6$\sigma$, and 38.8$\sigma$ levels and per cent-level constraints. Each technique offers unique information, with the strongest constraints achieved by using the three techniques in combination.

Line intensity mapping (LIM) offers a tomographic view of galaxy evolution by measuring the aggregate emission from unresolved galaxies. In the optical and near-infrared, the line emission is accompanied by much brighter continuum emission that must be removed to recover line auto- and cross-power spectra. We develop a forward-modeling framework using a ∼2deg^2 lightcone drawn from a cosmological N-body simulation populated with galaxies using a physics-based semi-analytic model (SAM). We construct intensity maps for the stellar continuum and for the strongest optical lines, Hα, Hβ, [O III] λ5007, and [O II] λ3727, including nebular dust attenuation tied to galaxy properties. From these cubes, we measure cross-channel angular power spectra, C_ℓ(λ_i,λ_j), and the normalized correlation matrix r_ij. In line-only maps, the correlation matrices show same-redshift ridges between emission lines, demonstrating how multi-line intensity mapping (MLIM) can isolate large-scale structure and probe dust attenuation. We show that dust suppresses the line cross-power by an amount that depends on galaxy properties, wavelength, and line pair, so a single overall amplitude cannot capture its effect. In total maps, however, the continuum dominates the raw correlations and hides much of the line-ridge structure. We therefore apply principal component analysis (PCA)-based spectral cleaning and quantify the line-transfer function using the simulation truth. Removing 20 PCA modes gives the best trade-off between line recovery and continuum suppression in our mock maps. Our results demonstrate the promise and challenges of extracting dust-sensitive LIM observables from SPHEREx-like observations, and highlight the need to model continuum cleaning and its transfer function in quantitative inference pipelines.

The James Webb Space Telescope (JWST) and Atacama Large Millimeter/submillimeter Array have detected emission lines from the ionized interstellar medium (ISM) in some of the first galaxies at z ≳ 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 subgrid 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 H ii regions within each simulated FIRE galaxy are modeled using the semianalytic HIIL ines code. A machine learning approach is then used to determine the conditional probability distribution for the line luminosity to stellar-mass ratio from the H ii 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 [O ii ], [O iii ], and Balmer line luminosities as a function of star formation rate agree well with current observations. Our predictions differ, however, from related works in the literature, which lack detailed subgrid ISM models. This highlights the importance of our multiscale simulation modeling framework. Finally, we provide forecasts for future line luminosity function measurements from the JWST and quantify the cosmic variance in such surveys.

The Primordial Inflation Explorer (PIXIE) is an Explorer-class mission concept to measure the energy spectrum and linear polarization of the cosmic microwave background (CMB). A single cryogenic Fourier transform spectrometer compares the sky to an external blackbody calibration target, measuring the Stokes I, Q, U parameters to levels 200 Jy/sr in each 2.65 degree diameter beam over the full sky, in each of 300 frequency channels from 28 GHz to 6 THz. With sensitivity over 1000 times greater than COBE/FIRAS, PIXIE opens a broad discovery space for the origin, contents, and evolution of the universe. Measurements of small distortions from a CMB blackbody spectrum provide a robust determination of the mean electron pressure and temperature in the universe while constraining processes including dissipation of primordial density perturbations, black holes, and the decay or annihilation of dark matter. Full-sky maps of linear polarization measure the optical depth to reionization at nearly the cosmic variance limit and constrain models of primordial inflation. Spectra with sub-percent absolute calibration spanning microwave to far-IR wavelengths provide a legacy data set for analyses including line intensity mapping of extragalactic emission and the cosmic infrared background amplitude and anisotropy. We describe the PIXIE instrument sensitivity, foreground subtraction, and anticipated science return from both the baseline 2-year mission and a potential extended mission.

The JWST and ALMA have detected emission lines from the ionized interstellar medium (ISM), including [OII], [OIII], and hydrogen Balmer series lines, in some of the first galaxies at z>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 given the huge dynamic range in spatial scales involved. 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, Mixture Density Network, 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 given its age, metallicity, and its galaxy's total stellar mass. 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 Illustris-TNG simulations at z=6. The resulting predictions for the [OII], [OIII], and Balmer line luminosities as a function of star-formation rate 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.

The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a balloon-borne telescope designed to survey star formation over cosmological time scales using intensity mapping in the 420 - 540 GHz frequency range. EXCLAIM uses a fully cryogenic telescope coupled to six on-chip spectrometers featuring kinetic inductance detectors (KIDs) to achieve high sensitivity, allowing for fast integration in dark atmospheric windows. The telescope receiver is cooled to approximate to 1.7 K by immersion in a superfluid helium bath and enclosed in a superfluid-tight shell with a meta-material anti-reflection coated silicon window. In addition to the optics and the spectrometer package, the receiver contains the magnetic shielding, the cryogenic segment of the spectrometer readout, and the sub-Kelvin cooling system. A three-stage continuous adiabatic demagnetization refrigerator (CADR) keeps the detectors at 100 mK while a He-4 sorption cooler provides a 900 mK thermal intercept for mechanical suspensions and coaxial cables. We present the design of the EXCLAIM receiver and report on the flight-like testing of major receiver components, including the superfluid-tight receiver window and the sub-Kelvin coolers.

Lensing reconstruction maps from the cosmic microwave background (CMB) provide direct observations of the matter distribution of the universe without the use of a biased tracer. Such maps, however, constitute projected observables along the line of sight that are dominated by their low-redshift contributions. To cleanly access high-redshift information, Maniyar et al., [Phys. Rev. D 105, 083509 (2022)] showed that a linear combination of lensing maps from both CMB and line intensity mapping (LIM) observations can exactly null the low-redshift contribution to CMB lensing convergence. In this paper we explore the scientific returns of this nulling technique. We show that LIM-nulling estimators can place constraints on standard Lambda CDM plus neutrino mass parameters that are competitive with traditional CMB lensing. Additionally, we demonstrate that as a clean probe of the high-redshift universe, LIM nulling can be used for model-independent tests of cosmology beyond Lambda CDM and as a probe of the high-redshift matter power spectrum.

Line intensity mapping (LIM) is a novel observational technique in astrophysics that utilizes the integrated emission from multiple atomic and molecular transition lines from galaxies to probe the complex physics of galaxy formation and evolution, as well as the large-scale structure of the universe. Modeling multiple line luminosities of galaxies with varying masses or their host halo masses poses significant uncertainty due to the lack of observational data across a wide redshift range and the intricate nature of astrophysical processes, making them challenging to model analytically or in simulations. While future experiments aim to measure multiple line intensities up to z∼ 8 across a wide volume using tomographic methods, we leverage publicly available datasets from the CMB experiment Planck and the galaxy survey eBOSS to constrain the CO(3-2) emission from galaxies. We correlate galaxies from eBOSS data onto the full-sky CO(2-1) map produced by Planck and report the first measurement of the average CO(3-2) intensity, I_CO = 45.7 ± 14.2 Jy/sr at z∼ 0.5 with 3.2σ confidence. Our findings demonstrate that stacking methods are already viable with existing observations from CMB experiments and galaxy surveys, and are complementary to traditional LIM experiments.

High resolution cosmic microwave background (CMB) experiments have allowed us to precisely measure the CMB temperature power spectrum down to very small scales (multipole $\ell \sim 3000$). Such measurements at multiple frequencies enable separating the primary CMB anisotropies with other signals like CMB lensing, thermal and kinematic Sunyaev-Zel'dovich effects (tSZ and kSZ), and cosmic infrared background (CIB). In this paper, we explore another signal of interest at these frequencies that should be present in the CMB maps: extragalactic CO molecular rotational line emissions, which are the most widely used tracers of molecular gas in the line intensity mapping experiments. Using the SIDES simulations adopted for top hat bandpasses at 150 and 220 GHz, we show that the cross-correlation of the CIB with CO lines has a contribution similar to the CIB-tSZ correlation and the kSZ power, thereby contributing a non-negligible amount to the total power at these scales. This signal, therefore, may significantly impact the recently reported $\geq 3\sigma$ detection of the kSZ power spectrum from the South Pole Telescope (SPT) collaboration, as the contribution of the CO lines is not considered in such analyses. Our results also provide a new way of measuring the CO power spectrum in cross-correlation with the CIB. Finally, these results show that the CO emissions present in the CMB maps will have to be accounted for in all the CMB auto-power spectrum and cross-correlation studies involving a LSS tracer.

The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a balloon-borne cryogenic telescope that will surv e y the spectrum of diffuse emission from both the Milky Way and the cosmic web to probe star formation, the interstellar medium, and galaxy evolution across cosmic time. EXCLAIM's primary extragalactic science surv e y maps 305 deg2 along the celestial equator with an R = 512 spectrometer o v er the frequenc y range ? = 420 - 540 GHz, targeting emission of the [C II ] line o v er redshifts 2.5 < z < 3.5 and several CO lines for z < 1. Cross-correlation with galaxy redshift catalogues isolates line emission from the large-scale structure at target redshifts. In this paper, we forecast the sensitivity for both the two-point and conditional one-point cross-correlation. We predict that EXCLAIM will detect both the [C II]-QSO cross-power spectrum and the conditional voxel intensity distribution (CVID) at various redshifts under a broad range of [C II ] intensity models, allowing it to differentiate among these models in the literature. These forecasts for the power spectra include the effects of line interlopers and continuum foreground contamination. We then convert the joint [C II ] constraints from both the cross-power spectrum and the CVID into constraints on the [C II ] halo luminosity-mass relation L-[CII]( M) model parameters and the star formation rate density (SFRD) from [C II ] emission. We also develop sensitivity estimates for CO, showing the ability to differentiate between models.

Line-intensity mapping (LIM) is a promising technique to constrain the global distribution of galaxy properties. To combine LIM experiments probing different tracers with traditional galaxy surveys and fully exploit the scientific potential of these observations, it is necessary to have a physically motivated modeling framework. As part of developing such a framework, in this work we introduce and model the conditional galaxy property distribution (CGPD), i.e. the distribution of galaxy properties conditioned on the host halo mass and redshift. We consider five galaxy properties, including the galaxy stellar mass, molecular gas mass, galaxy radius, gas phase metallicity and star formation rate (SFR), which are important for predicting the emission lines of interest. The CGPD represents the full distribution of galaxies in the five dimensional property space; many important galaxy distribution functions and scaling relations, such as the stellar mass function and SFR main sequence, can be derived from integrating and projecting it. We utilize two different kinds of cosmological galaxy simulations, a semi-analytic model and the IllustrisTNG hydrodynamic simulation, to characterize the CGPD and explore how well it can be represented using a Gaussian mixture model (GMM). We find that with just a few ($\sim 3$) Gaussian components, a GMM can describe the CGPD of the simulated galaxies to high accuracy for both simulations. The CGPD can be mapped to LIM or other observables by constructing the appropriate relationship between galaxy properties and the relevant observable tracers.

The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) will constrain star formation over cosmic time by carrying out a blind and complete census of redshifted carbon monoxide (CO) and ionized carbon ([CII]) emission in cross-correlation with galaxy survey data in redshift windows from the present to z=3.5 with a fully cryogenic, balloon-borne telescope. EXCLAIM will carry out extragalactic and Galactic surveys in a conventional balloon flight planned for 2023. EXCLAIM will be the first instrument to deploy µ-Spec silicon integrated spectrometers with a spectral resolving power R=512 covering 420-540 GHz. We summarize the design, science goals, and status of EXCLAIM.

We study background dynamics and the growth of matter perturbations in the extended quasidilaton setup of massive gravity. For the analysis of perturbations, we first choose a scalar field matter component and obtain the conditions under which all scalar perturbations are stable. We work in unitary gauge for the matter field, which allows us to directly map to known results in the limit of general relativity. By performing a parameter search, we find that the perturbations are unstable in general, while a particular choice of potential, where the scalar field effectively behaves like pressureless matter, allows for stable perturbations. We next consider the growth of matter perturbations in a cold dark matter-dominated Universe. Working in conformal Newtonian gauge, we obtain evolution equations for various observables including the growth factor and growth rate, and find scale-independent growth in the quasistatic and subhorizon approximations. We finally show how the Hubble parameter and matter perturbations evolve in massive gravity for a specific choice of parameter values, and how this evolution compares to the standard cosmological model consisting of a cosmological constant and cold dark matter.

Abhishek S. Maniyar, ∗ Emmanuel Schaan, 3, † and Anthony R. Pullen 4, ‡ Center for Cosmology and Particle Physics, Department of Physics, New York University, 726 Broadway, New York, NY, 10003, U.S.A. Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, CA 94720, USA Berkeley Center for Cosmological Physics, Department of Physics, University of California, Berkeley, CA 94720, USA Center for Computational Astrophysics, Flatiron Institute, New York, NY 10010, U.S.A.

Abstract. The experiment for cryogenic large-aperture intensity mapping (EXCLAIM) is a balloon-borne telescope designed to survey star formation in windows from the present to z  =  3.5. During this time, the rate of star formation dropped dramatically, while dark matter continued to cluster. EXCLAIM maps the redshifted emission of singly ionized carbon lines and carbon monoxide using intensity mapping, which permits a blind and complete survey of emitting gas through statistics of cumulative brightness fluctuations. EXCLAIM achieves high sensitivity using a cryogenic telescope coupled to six integrated spectrometers employing kinetic inductance detectors covering 420 to 540 GHz with spectral resolving power R  =  512 and angular resolution ≈4  arc min. The spectral resolving power and cryogenic telescope allow the survey to access dark windows in the spectrum of emission from the upper atmosphere. EXCLAIM will survey 305  deg2 in the Sloan Digital Sky Survey Stripe 82 field from a conventional balloon flight in 2023. EXCLAIM will also map several galactic fields to study carbon monoxide and neutral carbon emission as tracers of molecular gas. We summarize the design phase of the mission.

The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a balloon-borne far-infrared telescope that will survey galactic formation history over cosmological time scales with redshifts between 0 and 3.5. EXCLAIM will measure the statistics of brightness fluctuations of redshifted cumulative carbon monoxide and singly ionized carbon line emissions, following an intensity mapping approach. EXCLAIM will couple all-cryogenic optical elements to six μ-Spec spectrometer modules, operating at 420-540 GHz with a spectral resolution of 512 and featuring microwave kinetic inductance detectors. Here, we present an overview of the mission and its development status.

Circular polarization is a relatively unexplored realm of CMB physics. Given the substantial community effort towards building next generation CMB polarization experiments, including those which will be sensitive to circular polarization, it behooves theorists to understand the possible sources and relevant physics of circular polarization, as encoded in the Stokes V parameter. In this work we develop and derive the requisite formalism, namely the Boltzmann hierarchy for V-mode scalar, vector, and tensor, anisotropies. We derive the V-mode anisotropies induced by a general source term, and demonstrate how existing proposals for the generation of V can be incorporated as source terms in the Boltzmann hierarchy. A subset of these effects may be correlated with 21cm intensity; we provide a worked example and derive an estimator to extract this information from observations. We conclude by computing the CMB TV cross-correlation generated by axions, and find a relation between TV and VV spectra in axion models.

Understanding the non-linear dynamics of satellite halos (a.k.a. "sub-halos") is important for predicting the abundance and distribution of dark matter substructures and satellite galaxies, and for distinguishing among microphysical dark matter models using observations. Typically, modeling these dynamics requires large N-body simulations with high resolution. Semi-analytic models can provide a more efficient way to describe the key physical processes such as dynamical friction, tidal mass loss, and tidal heating, with only a few free parameters. In this work, we present a fast Monte Carlo Markov Chain fitting approach to explore the parameter space of such a sub-halo non-linear evolution model. We use the dynamical models described in an earlier work and calibrate the models to two sets of high-resolution cold dark matter N-body simulations, ELVIS and Caterpillar. Compared to previous calibrations that used manual parameter tuning, our approach provides a more robust way to determine the best-fit parameters and their posterior probabilities. We find that jointly fitting for the sub-halo mass and maximum velocity functions can break the degeneracy between tidal stripping and tidal heating parameters, as well as providing better constraints on the strength of dynamical friction. We show that our semi-analytic simulation can accurately reproduce N-body simulations statistics, and that the calibration results for the two sets of N-body simulations agree at 95% confidence level. Dynamical models calibrated in this work will be important for future dark matter substructure studies.