Observations of the Corona Borealis supercluster with the superextended Very Small Array: further constraints on the nature of the non-Gaussian CMB cold spot

TL;DR

This study uses high-resolution interferometric imaging to confirm a significant non-Gaussian cold spot in the CMB near the Corona Borealis supercluster, suggesting it may be caused by diffuse hot gas rather than primordial fluctuations.

Contribution

First detailed interferometric imaging of a deep CMB decrement in the Corona Borealis supercluster, confirming its non-Gaussian nature and exploring its possible origin in diffuse gas structures.

Findings

Confirmed the cold spot at -41 mJy/beam with high significance

Detected the feature in WMAP data consistent with SZ spectrum

Estimated a very low probability (0.19%) of Gaussian origin

Abstract

We present interferometric imaging at 33 GHz, with the new superextended configuration of the Very Small Array (VSA), of a very deep decrement in the cosmic microwave background (CMB) temperature. This decrement is located in the direction of the Corona Borealis supercluster, at a position with no known galaxy clusters, and was discovered by a previous VSA survey (Genova-Santos et al.). A total area of 3 sq.deg. has now been imaged, with an angular resolution of 7 arcmin and a flux sensitivity of 5 mJy/beam. These observations confirm the presence of this strong and resolved negative spot at -41+/-5 mJy/beam (-258+/-29 muK), with a signal to noise level of 8. This structure is also present in the WMAP 5-year data. The temperature of the W-band (94 GHz) data at the position of the decrement agrees within 1.2-sigma with that observed by the VSA at 33 GHz, and within 0.2-sigma with the Sunyaev-Zel'dovich (SZ) spectrum. Our analyses show that it is a non-Gaussian feature in the CMB at a level of 4.8-sigma. The probability of finding such a deviation or larger in CMB Gaussian simulations is only 0.19 per cent. Therefore, an explanation other than primordial CMB is required. We have considered the possibility of an SZ effect generated in a diffuse, extended warm/hot gas distribution. This hypothesis is especially relevant, as the presence of such structures, if confirmed, could provide the location for a significant fraction of the missing baryons in the Local Universe.