Overview and status of EXCLAIM, the experiment for cryogenic large-aperture intensity mapping

Abstract

The EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM) is a balloon-borne far-infrared telescope that will survey star formation history over cosmological time scales to improve our understanding of why the star formation rate declined at redshift z < 2, despite continued clustering of dark matter. Specifically, EXCLAIM will map the emission of redshifted carbon monoxide and singly-ionized carbon lines in windows over a redshift range 0 < z < 3.5, following an innovative approach known as intensity mapping. Intensity mapping measures the statistics of brightness fluctuations of cumulative line emissions instead of detecting individual galaxies, thus enabling a blind, complete census of the emitting gas. To detect this emission unambiguously, EXCLAIM will cross-correlate with a spectroscopic galaxy catalog. The EXCLAIM mission uses a cryogenic design to cool the telescope optics to approximately 1.7 K. The telescope features a 90-cm primary mirror to probe spatial scales on the sky from the linear regime up to shot noise-dominated scales. The telescope optical elements couple to six µ-Spec spectrometer modules, operating over a 420-540 GHz frequency band with a spectral resolution of 512 and featuring microwave kinetic inductance detectors. A Radio Frequency System-on-Chip (RFSoC) reads out the detectors in the baseline design. The cryogenic telescope and the sensitive detectors allow EXCLAIM to reach high sensitivity in spectral windows of low emission in the upper atmosphere. Here, an overview of the mission design and development status since the start of the EXCLAIM project in early 2019 is presented.

On estimating the cosmic molecular gas density from CO Line Intensity Mapping observations

“…The Carbon Monoxide Mapping Array Project (COMAP Li et al 2016) targets the CO(1-0) emission line at z = 2.4 − 3.4, right in the middle of the mmIME redshift range and near the excess CII emission seen in the Planck data, and would provide a highly complementary molecular gas measurement over a much larger intensity mapping volume. The Experiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM Cataldo et al 2021) will probe the CII line in a similar redshift range, and will offer an improved measurement of that line to improve upon the Planck measurement. Several other reionization-focused projects have a mmIME-like ladder of CO lines as a "foreground" to their higher-redshift science (Lagache 2018;Stacey et al 2018;Sun et al 2020).…”

“…For molecular gas studies, LIM observations of CO lines are sensitive to fainter galaxies inaccessible to direct imaging, allowing population-wide examination of this crucial ISM component. First discussed in Righi et al (2008), this application of LIM has garnered significant interest (Lidz et al 2011;Pullen et al 2013;Breysse et al 2014Breysse et al , 2016Breysse & Rahman 2017;Fonseca et al 2017;Padmanabhan 2018;Breysse & Alexandroff 2019;Chung et al 2019;Moradinezhad Dizgah & Keating 2019), with a number of experimental efforts planned or in progress (Li et al 2016;Lagache 2018;Stacey et al 2018;Sun et al 2020;Cataldo et al 2021). Two of these experiments, the CO Power Spectrum Survey (COPSS, Keating et al 2016) and the Millimeter Intensity Mapping Experiment (mmIME, Keating et al 2020, hereafter K20), have reported 2 and 4 − σ detections of unresolved CO emission respectively.…”

Superfluid Liquid Helium Control for the Primordial Inflation Polarization Explorer Balloon Payload

“…PIPER extends comparable open-aperture operation to larger apertures and frequencies 200-600 GHz [5]. The EXCLAIM balloon mission [21] plans to use a similar approach for 1 m optics at far-infrared wavelengths, while the BOBCAT program [22] seeks to fly cold 3-4 meter optics. We describe the superfluid pumps for the PIPER balloon payload and discuss the thermal performance and cryogenic managment of the PIPER payload for two flights in 2017 and 2019.…”

Analytical covariance between voxel intensity distributions and line-intensity mapping power spectra

“…In addition, several other line transitions at higher frequencies have garnered attention as probes of the different phases of the interstellar medium, such as the rotational lines of carbon monoxide (CO) [12][13][14][15][16], the fine structure line of ionized carbon ([CII]) [17,18], Hα and Hβ [19,20], Lyman-α [21,22], and oxygen lines [19]. A vast number of experiments that target these spectral lines are already observing or currently under development (see e.g., [23][24][25][26][27][28]), with some initial constraints and tentative power spectrum detections [18,[29][30][31][32][33][34].…”