HI constraints from the cross-correlation of eBOSS galaxies and Green Bank Telescope intensity maps

Abstract

We present the joint analysis of Neutral Hydrogen (H ) Intensity Mapping observations with three galaxy samples: the Luminous Red Galaxy (LRG) and Emission Line Galaxy (ELG) samples from the eBOSS survey, and the WiggleZ Dark Energy Survey sample. The H intensity maps are Green Bank Telescope observations of the redshifted 21cm emission on 100 deg 2 covering the redshift range 0.6 < 𝑧 < 1.0. We process the data by separating and removing the foregrounds present in the radio frequencies with F ICA. We verify the quality of the foreground separation with mock realisations, and construct a transfer function to correct for the effects of foreground removal on the H signal. We cross-correlate the cleaned H data with the galaxy samples and study the overall amplitude as well as the scale-dependence of the power spectrum. We also qualitatively compare our findings with the predictions by a semi-analytic galaxy evolution simulation. The cross-correlations constrain the quantity Ω H 𝑏 H 𝑟 H ,opt at an effective scale 𝑘 eff , where Ω H is the H density fraction, 𝑏 H is the H bias, and 𝑟 H ,opt the galaxyhydrogen correlation coefficient, which is dependent on the H content of the optical galaxy sample. At 𝑘 eff = 0.31 ℎ/Mpc we find Ω H 𝑏 H 𝑟 H ,Wig = [0.58 ± 0.09 (stat) ± 0.05 (sys)] × 10 −3 for GBT-WiggleZ, Ω H 𝑏 H 𝑟 H ,ELG = [0.40 ± 0.09 (stat) ± 0.04 (sys)] × 10 −3 for GBT-ELG, and Ω H 𝑏 H 𝑟 H ,LRG = [0.35 ± 0.08 (stat) ± 0.03 (sys)] × 10 −3 for GBT-LRG, at 𝑧 0.8. We also report results at 𝑘 eff = 0.24 ℎ/Mpc and 𝑘 eff = 0.48 ℎ/Mpc. With little information on H parameters beyond our local Universe, these are amongst the most precise constraints on neutral hydrogen density fluctuations in an underexplored redshift range.

The HI intensity mapping bispectrum including observational effects

“…The impact on the mock clustering statistics is then used to construct the transfer function which is applied to the real data to reverse the H signal loss effects from the foreground clean. This technique has been used for H IM power spectra measurements with pathfinder surveys (Masui et al 2013;Switzer et al 2013;Anderson et al 2018;Wolz et al 2021). However, using this in the context of a bispectrum measurement would be more cumbersome and computationally expensive.…”

An Intensity Mapping Constraint on the CO-Galaxy Cross Power Spectrum at Redshift ~ 3

“…Cross-correlation also serves as a check on systematics in intensity mapping data, and can be used to validate detections of the auto-correlation power spectrum (Furlanetto & Lidz 2007;Silva et al 2015). This is true not only for CO but also ongoing hydrogen 21cm and [C II] 158µm intensity mapping projects (Chang et al 2010;Masui et al 2013;Wolz et al 2021).…”

Constraining low redshift [CII] Emission by Cross-Correlating FIRAS and BOSS Data

“…Intensity mapping has developed rapidly in the past fifteen years. Pathfinding intensity mapping surveys have used pre-existing telescopes to detect aggregate emission from the 21-cm line of neutral hydrogen (HI) (Pen et al 2009;Chang et al 2010;Masui et al 2013;Switzer et al 2013;Wolz et al 2017;Anderson et al 2018;Wolz et al 2021) via cross-correlation with optical galaxy surveys. Several dedicated 21-cm intensity mapping experiments are now underway, targeting both the epoch of reionization (e.g., LOFAR, van Haarlem et al (2013), andSKA precursors HERA andMWA, DeBoer et al (2017); McKinley et al (2018)) as well as the era of dark energy dominance (e.g., CHIME, Bandura et al (2014), Tianlai, Chen (2012), HIRAX, Crichton et al (2021), SKA precursor MeerKAT, Wang et al (2021), and BINGO, Abdalla et al (2021)).…”