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1. COMAP Pathfinder – Season 2 results: III. Implications for cosmic molecular gas content at z ~ 3

   https://doi.org/10.1051/0004-6361/202451122  

   Chung, D T; Breysse, P C; Cleary, K A; Dunne, D A; Lunde, J_G S; Padmanabhan, H; Stutzer, N-O; Tolgay, D; Bond, J R; Church, S E; et al (November 2024, Astronomy & Astrophysics)

   The Carbon monOxide Mapping Array Project (COMAP) Pathfinder survey continues to demonstrate the feasibility of line-intensity mapping using high-redshift carbon monoxide (CO) line emission traced at cosmological scales. The latest COMAP Pathfinder power spectrum analysis is based on observations through the end of Season 2, covering the first three years of Pathfinder operations. We use our latest constraints on the CO(1–0) line-intensity power spectrum atz~ 3 to update corresponding constraints on the cosmological clustering of CO line emission and thus the cosmic molecular gas content at a key epoch of galaxy assembly. We first mirror the COMAP Early Science interpretation, considering how Season 2 results translate to limits on the shot noise power of CO fluctuations and the bias of CO emission as a tracer of the underlying dark matter distribution. The COMAP Season 2 results place the most stringent limits on the CO tracer bias to date, at ⟨T b⟩ < 4.8 μK, which translates to a molecular gas density upper limit ofρ_H2< 1.6 × 10⁸M_⊙Mpc⁻³atz~ 3 given additional model assumptions. These limits narrow the model space significantly compared to previous CO line-intensity mapping results while maintaining consistency with small-volume interferometric surveys of resolved line candidates. The results also express a weak preference for CO emission models used to guide fiducial forecasts from COMAP Early Science, including our data-driven priors. We also consider directly constraining a model of the halo–CO connection, and show qualitative hints of capturing the total contribution of faint CO emitters through the improved sensitivity of COMAP data. With continued observations and matching improvements in analysis, the COMAP Pathfinder remains on track for a detection of cosmological clustering of CO emission. 

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2. Boosting line intensity map signal-to-noise ratio with the Ly-α forest cross-correlation

   https://doi.org/10.1093/mnras/stad1906  

   Qezlou, Mahdi; Bird, Simeon; Lidz, Adam; Sun, Guochao; Newman, Andrew_B; Rudie, Gwen_C; Ni, Yueying; Croft, Rupert; Di Matteo, Tiziana (June 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We forecast the prospects for cross-correlating future line intensity mapping (LIM) surveys with the current and future Ly-α forest measurements. Using large cosmological hydrodynamic simulations, we model the emission from the CO rotational transition in the CO Mapping Array Project LIM experiment at the 5-yr benchmark and the Ly-α forest absorption signal for extended Baryon Acoustic Oscillations (BOSS), Dark energy survey instrument (DESI), and Prime Focus multiplex Spectroscopy survey (PFS). We show that CO × Ly-α forest significantly enhances the detection signal-to-noise ratio (S/N) of CO, with up to $$300{{\ \rm per\, cent}}$$ improvement when correlated with the PFS Ly-α forest survey and a 50–75 per cent enhancement with the available eBOSS or the upcoming DESI observations. This is competitive with even CO × spectroscopic galaxy surveys. Furthermore, our study suggests that the clustering of CO emission is tightly constrained by CO × Ly-α forest due to the increased sensitivity and the simplicity of Ly-α absorption modelling. Foreground contamination or systematics are expected not to be shared between LIM and Ly-α forest observations, providing an unbiased inference. Ly-α forest will aid in detecting the first LIM signals. We also estimate that [C ii] × Ly-α forest measurements from Experiment for Cryogenic Large-Aperture Intensity Mapping and DESI/eBOSS should have a larger S/N than planned [C ii] × quasar observations by about an order of magnitude. 

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3. COMAP Early Science. VIII. A Joint Stacking Analysis with eBOSS Quasars

   Dunne, Delaney A; Cleary, Kieran A; Breysse, Patrick C; Chung, Dongwoo T; Ihle, Havard T; Bond, J Richard; Eriksen, Hans_Kristian; Gundersen, Joshua_Ott; Keating, Laura C; Kim, Junhan; et al (April 2024, Astrophysical journal)

   We present a new upper limit on the cosmic molecular gas density at z=2.4−3.4 obtained using the first year of observations from the CO Mapping Array Project (COMAP). COMAP data cubes are stacked on the 3D positions of 243 quasars selected from the Extended Baryon Oscillation Spectroscopic Survey (eBOSS) catalog, yielding a 95% upper limit for flux from CO(1-0) line emission of 0.129 Jy km/s. Depending on the balance of the emission between the quasar host and its environment, this value can be interpreted as an average CO line luminosity L′CO of eBOSS quasars of ≤1.26×1011 K km pc2 s−1, or an average molecular gas density ρH2 in regions of the universe containing a quasar of ≤1.52×108 M⊙ cMpc−3. The L′CO upper limit falls among CO line luminosities obtained from individually-targeted quasars in the COMAP redshift range, and the ρH2 value is comparable to upper limits obtained from other Line Intensity Mapping (LIM) surveys and their joint analyses. Further, we forecast the values obtainable with the COMAP/eBOSS stack after the full 5-year COMAP Pathfinder survey. We predict that a detection is probable with this method, depending on the CO properties of the quasar sample. Based on the achieved sensitivity, we believe that this technique of stacking LIM data on the positions of traditional galaxy or quasar catalogs is extremely promising, both as a technique for investigating large galaxy catalogs efficiently at high redshift and as a technique for bolstering the sensitivity of LIM experiments, even with a fraction of their total expected survey data. 

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4. Design of the SPT-SLIM Focal Plane: A Spectroscopic Imaging Array for the South Pole Telescope

   https://doi.org/10.1007/s10909-022-02843-4  

   Barry, P. S.; Anderson, A.; Benson, B.; Carlstrom, J. E.; Cecil, T.; Chang, C.; Dobbs, M.; Hollister, M.; Karkare, K. S.; Keating, G. K.; et al (September 2022, Journal of Low Temperature Physics)

   Abstract The Summertime Line Intensity Mapper (SLIM) is a mm-wave line-intensity mapping (mm-LIM) experiment for the South Pole Telescope (SPT). The goal of SPT-SLIM is to serve as a technical and scientific pathfinder for the demonstration of the suitability and in-field performance of multi-pixel superconducting filterbank spectrometers for future mm-LIM experiments. Scheduled to deploy in the 2023-24 austral summer, the SPT-SLIM focal plane will include 18 dual-polarisation pixels, each coupled to an$$R = \lambda / \Delta \lambda = 300$$ $R=\lambda /\Delta \lambda =300$thin-film microstrip filterbank spectrometer that spans the 2 mm atmospheric window (120–180 GHz). Each individual spectral channel feeds a microstrip-coupled lumped-element kinetic inductance detector, which provides the highly multiplexed readout for the 10k detectors needed for SPT-SLIM. Here, we present an overview of the preliminary design of key aspects of the SPT-SLIM focal plane array, a description of the detector architecture and predicted performance, and initial test results that will be used to inform the final design of the SPT-SLIM spectrometer array. 

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5. Constraining the star formation rate using joint CIB continuum and C ii intensity mapping

   https://doi.org/10.1093/mnras/stad2172  

   Zhou, Zilu; Maniyar, Abhishek_S; Pullen, Anthony_R (July 2023, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT Line intensity mapping (LIM) experiments probing the nearby Universe can expect a considerable amount of cosmic infrared background (CIB) continuum emission from near and far-infrared galaxies. For the purpose of using LIM to constrain the star formation rate (SFR), we argue that the CIB continuum – traditionally treated as contamination – can be combined with the LIM signal to enhance the SFR constraints achievable. We first present a power spectrum model that combines continuum and line emissions assuming a common SFR model. We subsequently analyse the effectiveness of the joint model in the context of the EXperiment for Cryogenic Large-Aperture Intensity Mapping (EXCLAIM), which utilizes the $$[{\rm C\, \small {II}}]$$ molecular line to study the SFR. We numerically compute the theoretical power spectra according to our model and the EXCLAIM survey specifics, and perform Fisher analysis to forecast the SFR constraints. We find that although the joint model has no considerable advantage over LIM alone assuming the current survey level of EXCLAIM, its effects become significant when we consider more optimistic values of survey resolution and angular span that are expected of future LIM experiments. We show that the CIB is not only an additional SFR sensitive signal, but also serves to break the SFR parameter degeneracy that naturally emerges from the $$[{\rm C\, \small {II}}]$$ Fisher matrix. For this reason, addition of the CIB will allow improvements in the survey parameters to be better reflected in the SFR constraints, and can be effectively utilized by future LIM experiments. 

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