The CMB Cold Spot as predicted by foregrounds around nearby galaxies

LAMBAS, DIEGO GARCIA; HANSEN, FRODE K.; TOSCANO, FACUNDO; LUPARELLO, HELIANA E.; BOERO, EZEQUIEL F.

ASTRONOMY AND ASTROPHYSICS

EDP SCIENCES S A

Lugar: Paris; Año: 2023 vol. 681

0004-6361

Context. The non-Gaussian Cold Spot surrounded by its hot ring is one of the most striking features of the cosmic microwavebackground (CMB) and has generated significant attention in the literature. It has been speculated that either new physics or theIntegrated Sachs-Wolfe effect induced by the presence of a cosmic void at relatively high redshift could account for the observations.Aims. Here, we investigate if the newly discovered systematic decrease in the CMB temperature in the neighbourhood of nearbygalaxies may create such a strong temperature depression. In particular, we note that the largest galaxy group complex in the localUniverse, the Eridanus super-group with its neighbouring groups, is in the Cold Spot area. Our goal is to analyse observational galaxydata to characterise the neighbourhood of the Cold Spot, explore the properties of these galaxies, and thereby make a prediction ofthe galaxy induced CMB temperature decrement in this region.Methods. We used the Planck SMICA maps, and as foreground tracers, galaxies from the publicly available observational catalogues:2MRS, 6dF, and HIPASS, which include information on redshifts, positions, magnitudes, and other astrophysical characteristics.We applied previously explored mean temperature profile shapes to model the expected temperature decrement from the galaxies inthe Cold Spot area.Results. Even after correcting for the mean low temperature of the Cold Spot region, we find that the temperature decrement aroundgalaxies is significantly stronger than the mean decrement in other parts of the sky. We discuss whether this could be attributed to thefact that the Cold Spot area coincides with one of the regions populated by the most HI deficient galaxies. Modeling the foregroundtemperature profile that is mainly associated with spiral galaxies in this location, we find a particularly strong temperature decrementdue to the presence of the late-type overabundant largest group complex in the nearby universe. A Cold Spot shape that largelyoverlaps with the CMB Cold Spot is observed.Conclusions. We conclude that the coincidence of the only nearby spiral-rich group complex located in the Cold Spot region, and thesuccess of the modelling performed, adds strong evidence to the existence of a local extragalactic foreground that may account for theobserved temperature depression, alleviating the tension with the Gaussian field that is otherwise expected in the CMB.