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1. COMAP Early Science. III. CO Data Processing

   https://doi.org/10.3847/1538-4357/ac63ca  

   Foss, Marie K. ; Ihle, Håvard T. ; Borowska, Jowita ; Cleary, Kieran A. ; Eriksen, Hans Kristian ; Harper, Stuart E. ; Kim, Junhan ; Lamb, James W. ; Lunde, Jonas G. S. ; Philip, Liju ; et al ( July 2022 , The Astrophysical Journal)

   We describe the first-season CO Mapping Array Project (COMAP) analysis pipeline that converts raw detector readouts to calibrated sky maps. This pipeline implements four main steps: gain calibration, filtering, data selection, and mapmaking. Absolute gain calibration relies on a combination of instrumental and astrophysical sources, while relative gain calibration exploits real-time total-power variations. High-efficiency filtering is achieved through spectroscopic common-mode rejection within and across receivers, resulting in nearly uncorrelated white noise within single-frequency channels. Consequently, near-optimal but biased maps are produced by binning the filtered time stream into pixelized maps; the corresponding signal bias transfer function is estimated through simulations. Data selection is performed automatically through a series of goodness-of-fit statistics, includingχ²and multiscale correlation tests. Applying this pipeline to the first-season COMAP data, we produce a data set with very low levels of correlated noise. We find that one of our two scanning strategies (the Lissajous type) is sensitive to residual instrumental systematics. As a result, we no longer use this type of scan and exclude data taken this way from our Season 1 power spectrum estimates. We perform a careful analysis of our data processing and observing efficiencies and take account of planned improvements to estimate our future performance. Power spectrum results derived from the first-season COMAP maps are presented and discussed in companion papers.

    

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2. BICEP/Keck. XVII. Line-of-sight Distortion Analysis: Estimates of Gravitational Lensing, Anisotropic Cosmic Birefringence, Patchy Reionization, and Systematic Errors

   https://doi.org/10.3847/1538-4357/acc85c  

   Ade, P. A. R. ; Ahmed, Z. ; Amiri, M. ; Barkats, D. ; Thakur, R. Basu ; Bischoff, C. A. ; Beck, D. ; Bock, J. J. ; Boenish, H. ; Bullock, E. ; et al ( May 2023 , The Astrophysical Journal)

   We present estimates of line-of-sight distortion fields derived from the 95 and 150 GHz data taken by BICEP2, BICEP3, and the Keck Array up to the 2018 observing season, leading to cosmological constraints and a study of instrumental and astrophysical systematics. Cosmological constraints are derived from three of the distortion fields concerning gravitational lensing from large-scale structure, polarization rotation from magnetic fields or an axion-like field, and the screening effect of patchy reionization. We measure an amplitude of the lensing power spectrum$A_L^{\varphi \varphi }=0.95\pm 0.20$. We constrain polarization rotation, expressed as the coupling constant of a Chern–Simons electromagnetic termg_aγ≤ 2.6 × 10⁻²/H_I, whereH_Iis the inflationary Hubble parameter, and an amplitude of primordial magnetic fields smoothed over 1 MpcB_1Mpc≤ 6.6 nG at 95 GHz. We constrain the rms of optical depth fluctuations in a simple “crinkly surface” model of patchy reionization, findingA^τ< 0.19 (2σ) for the coherence scale ofL_c= 100. We show that all of the distortion fields of the 95 and 150 GHz polarization maps are consistent with simulations including lensed ΛCDM, dust, and noise, with no evidence for instrumental systematics. In some cases, theEBandTBquadratic estimators presented here are more sensitive than our previous map-based null tests at identifying and rejecting spuriousB-modes that might arise from instrumental effects. Finally, we verify that the standard deprojection filtering in the BICEP/Keck data processing is effective at removing temperature to polarization leakage.

    

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3. First Results from HERA Phase I: Upper Limits on the Epoch of Reionization 21 cm Power Spectrum

   https://doi.org/10.3847/1538-4357/ac1c78  

   Abdurashidova, Zara ; Aguirre, James E. ; Alexander, Paul ; Ali, Zaki S. ; Balfour, Yanga ; Beardsley, Adam P. ; Bernardi, Gianni ; Billings, Tashalee S. ; Bowman, Judd D. ; Bradley, Richard F. ; et al ( February 2022 , The Astrophysical Journal)

   Abstract We report upper limits on the Epoch of Reionization 21 cm power spectrum at redshifts 7.9 and 10.4 with 18 nights of data (∼36 hr of integration) from Phase I of the Hydrogen Epoch of Reionization Array (HERA). The Phase I data show evidence for systematics that can be largely suppressed with systematic models down to a dynamic range of ∼10 9 with respect to the peak foreground power. This yields a 95% confidence upper limit on the 21 cm power spectrum of Δ 21 2 ≤ ( 30.76 ) 2 mK 2 at k = 0.192 h Mpc −1 at z = 7.9, and also Δ 21 2 ≤ ( 95.74 ) 2 mK 2 at k = 0.256 h Mpc −1 at z = 10.4. At z = 7.9, these limits are the most sensitive to date by over an order of magnitude. While we find evidence for residual systematics at low line-of-sight Fourier k ∥ modes, at high k ∥ modes we find our data to be largely consistent with thermal noise, an indicator that the system could benefit from deeper integrations. The observed systematics could be due to radio frequency interference, cable subreflections, or residual instrumental cross-coupling, and warrant further study. This analysis emphasizes algorithms that have minimal inherent signal loss, although we do perform a careful accounting in a companion paper of the small forms of loss or bias associated with the pipeline. Overall, these results are a promising first step in the development of a tuned, instrument-specific analysis pipeline for HERA, particularly as Phase II construction is completed en route to reaching the full sensitivity of the experiment. 

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4. An Intensity Mapping Constraint on the CO-galaxy Cross-power Spectrum at Redshift ∼3

   https://doi.org/10.3847/1538-4357/ac4888  

   Keenan, Ryan P. ; Keating, Garrett K. ; Marrone, Daniel P. ( March 2022 , The Astrophysical Journal)

   The abundance of cold molecular gas plays a crucial role in models of galaxy evolution. While deep spectroscopic surveys of CO emission lines have been a primary tool for measuring this abundance, the difficulty of these observations has motivated alternative approaches to studying molecular gas content. One technique, line intensity mapping, seeks to constrain the average molecular gas properties of large samples of individually undetectable galaxies through the CO brightness power spectrum. Here we present constraints on the cross-power spectrum between CO intensity maps and optical galaxy catalogs. This cross-measurement allows us to check for systematic problems in CO intensity mapping data, and validate the data analysis used for the auto-power spectrum measurement of the CO Power Spectrum Survey. We place a 2σupper limit on the band-averaged CO-galaxy cross-power ofP_×< 540μK h⁻³Mpc³. Our measurement favors a nonzero 〈T_CO〉 at around 90% confidence and gives an upper limit on the mean molecular gas density atz∼ 2.6 of 7.7 × 10⁸M_⊙Mpc⁻³. We forecast the expected cross-power spectrum by applying a number of literature prescriptions for the CO luminosity–halo mass relation to a suite of mock light cones. Under the most optimistic forecasts, the cross-spectrum could be detected with only moderate extensions of the data used here, while more conservative models could be detected with a factor of 10 increase in sensitivity. Ongoing CO intensity mapping experiments will target fields allowing for extensive cross-correlation analysis and should reach the sensitivity required to detect the cross-spectrum signal.

    

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5. New EoR power spectrum limits from MWA Phase II using the delay spectrum method and novel systematic rejection

   https://doi.org/10.1093/mnras/stad845  

   Kolopanis, Matthew ; Pober, Jonathan C. ; Jacobs, Daniel C. ; McGraw, Samantha ( March 2023 , Monthly Notices of the Royal Astronomical Society)

   We present an analysis of Epoch of Reionization (EoR) data from Phase II of the Murchison Widefield Array using the simpleds delay spectrum pipeline. Prior work analysed the same observations using the fhd/εppsilon imaging pipeline, and so the present analysis represents the first time that both principal types of 21 cm cosmology power spectrum estimation approaches have been applied to the same data set. Our limits on the 21 cm power spectrum amplitude span a range in k space of $|k| \lt 1 \, h_{100}\, {\rm Mpc}^{-1}$ with a lowest measurement of Δ2(k) ≤ 4.58 × 103 mK2 at $k = 0.190\, h_{100}\, \rm {Mpc}^{-1}$ and z = 7.14. In order to achieve these limits, we need to mitigate a previously unidentified common mode systematic in the data set. If not accounted for, this systematic introduces an overall negative bias that can make foreground contaminated measurements appear as stringent, noise-limited constraints on the 21 cm signal amplitude. The identification of this systematic highlights the risk in modelling systematics as positive-definite contributions to the power spectrum and in ‘conservatively’ interpreting all measurements as upper limits.

    

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