Revealing cosmological fluctuations in 21 cm intensity maps with MeerKLASS: from maps to power spectra

Abstract Mapping the integrated 21 cm emission line from dark matter-tracing neutral hydrogen gas is the primary science goal for MeerKLASS (MeerKAT’s Large Area Synoptic Survey). Prior to the arrival of MeerKAT, this intensity mapping technique had only been tested on a couple of pre-existing single-dish radio telescopes with a handful of observational hours with which to make early pioneering detections. The 64-dish MeerKAT array, precursor to the SKA Observatory (SKAO), can scan the sky in auto-correlation (or single-dish ) mode and perform intensity mapping across large sky areas, presenting the exciting potential for a wide area ( ${\gtrsim }\,10{,}000\,{\mathrm{deg}}^{2}$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>≳</mml:mo> <mml:mspace/> <mml:mn>10</mml:mn> <mml:mo>,</mml:mo> <mml:mn>000</mml:mn> <mml:mspace/> <mml:msup> <mml:mi>deg</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:math> ) spectroscopic survey across redshift $0.4\,{&lt;}\,z\,{&lt;}\,1.45$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mn>0.4</mml:mn> <mml:mspace/> <mml:mo>&lt;</mml:mo> <mml:mspace/> <mml:mi>z</mml:mi> <mml:mspace/> <mml:mo>&lt;</mml:mo> <mml:mspace/> <mml:mn>1.45</mml:mn> </mml:math> . Validating the single-dish mode of observation for a multi-dish array and developing the analysis pipeline with which to make unbiased measurements has presented major challenges to this endeavour. In this work, we overview the advances in the field that have facilitated a robust analysis framework for single-dish intensity mapping, and review some results that showcase its success using early MeerKLASS surveys. We demonstrate our control of foreground cleaning, signal loss and map regridding to deliver detections of cosmological clustering within the intensity maps through cross-correlation power spectrum measurements with overlapping galaxy surveys. Finally, we discuss the prospects for future MeerKLASS observations and forecast its potential, making our code publicly available: .