[Paper Review] Extragalactic Science with the Experiment for Cryogenic Large-aperture Intensity Mapping

Anthony R. Pullen, Patrick C. Breysse+15 more|arXiv (Cornell University)|Sep 6, 2022

Superconducting and THz Device Technology4 citations

TL;DR

This paper forecasts the extragalactic science potential of EXCLAIM, a balloon-borne cryogenic telescope using line intensity mapping (LIM) to survey [CII] at z=2.5–3.5 and CO lines at z<1. It predicts EXCLAIM will detect the [CII]-quasar cross-power spectrum and conditional voxel intensity distribution with high significance, enabling constraints on the [CII] halo luminosity-mass relation and star formation rate density (SFRD) at z≈2.7 with a signal-to-noise ratio of ~4.

ABSTRACT

The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a balloon-borne cryogenic telescope that will survey 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 survey maps 305 deg$^2$ along the celestial equator with an R=512 spectrometer over the frequency range ν=420-540 GHz, targeting emission of the [CII] line over redshifts 2.5

Motivation & Objective

• To forecast the sensitivity of the EXperiment for Cryogenic Large-aperture Intensity Mapping (EXCLAIM) to extragalactic [CII] and CO line emission across cosmic time.
• To assess EXCLAIM’s ability to distinguish between competing models of [CII] intensity and CO emission in the literature.
• To demonstrate that joint measurements of the cross-power spectrum and conditional voxel intensity distribution (CVID) can constrain the [CII] luminosity-mass relation and star formation rate density (SFRD).
• To evaluate the potential of EXCLAIM to detect the baryon acoustic oscillation (BAO) signature in the [CII] power spectrum for H(z) measurements at z≈2.7.
• To establish EXCLAIM as a pathfinder for future space- and balloon-borne LIM missions targeting cosmological and galaxy evolution science.

Proposed method

• EXCLAIM employs a cryogenic, large-aperture telescope on a high-altitude balloon to map diffuse submillimeter emission across 305 deg² along the celestial equator.
• The instrument uses a high-resolution spectrometer (R=512) covering 420–540 GHz to target the [CII] 158 μm line at z=2.5–3.5 and CO rotational lines (J=4–7) at z<1.
• Cross-correlation of EXCLAIM’s intensity maps with external quasar and galaxy redshift catalogs isolates line emission from large-scale structure at target redshifts.
• Statistical forecasts are generated using the cross-power spectrum and conditional voxel intensity distribution (CVID), incorporating realistic noise, line interlopers, and continuum foregrounds.
• The [CII] intensity models are propagated through the power spectrum and CVID forecasts to derive constraints on the [CII] luminosity-mass relation and SFRD.
• Sensitivity estimates for CO are derived by modeling emission from different CO transitions and comparing predicted signal-to-noise ratios across literature models.

Experimental results

Research questions

• RQ1 Can EXCLAIM detect the [CII]-quasar cross-power spectrum at z≈3 with high significance across a range of [CII] intensity models?
• RQ2 Can the conditional voxel intensity distribution (CVID) of [CII] emission be measured with high precision by EXCLAIM at z≈2.7?
• RQ3 To what extent can joint constraints from the cross-power spectrum and CVID differentiate between competing [CII] luminosity-mass relation models in the literature?
• RQ4 What is the expected signal-to-noise ratio (SNR) for EXCLAIM’s measurement of the star formation rate density (SFRD) from [CII] emission at z≈2.7?
• RQ5 Can EXCLAIM detect the baryon acoustic oscillation (BAO) signature in the [CII] power spectrum at z≈2.7, and what would be its sensitivity to H(z) measurements?

Key findings

• EXCLAIM is forecast to detect the [CII]-quasar cross-power spectrum with a signal-to-noise ratio (SNR) of 7–11 at z≈2.7, depending on the [CII] intensity model.
• The conditional voxel intensity distribution (CVID) of [CII] emission can be measured by EXCLAIM with high precision, enabling robust constraints on [CII] emission models.
• Joint use of the cross-power spectrum and CVID forecasts will allow EXCLAIM to constrain the [CII] luminosity-mass relation $L_{\mathrm{[CII]}}(M)$ with high fidelity.
• EXCLAIM is predicted to measure the star formation rate density (SFRD) at z≈2.7 with a signal-to-noise ratio of approximately 4, offering a global measurement inclusive of faint, undetected galaxies.
• The [CII] power spectrum at z≈2.7 is expected to exhibit a detectable baryon acoustic oscillation (BAO) signature with SNR in the range 7–11, enabling H(z) measurements at this redshift.
• EXCLAIM’s LIM measurements are expected to be insensitive to uncertainties in the overall [CII] intensity amplitude, as the BAO scale is independent of the power spectrum amplitude, making H(z) measurements robust.