Detalles de publicación
PP 08030
Observations of the Corona Borealis supercluster with the superextended Very Small Array: further constraints on the nature of the non-Gaussian CMB cold spot
(1) Instituto de Astrofísica de Canarias
(2) Astrophysics Group, Cavendish Laboratory, University of Cambridge
(3) Jodrell Bank Centre for Astrophysics, University of Manchester
(4) Consejo Superior de Investigaciones Científicas
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 (Génova-Santos et al.). A total area of 3 square degrees 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 -37+/-5 mJy/beam (-229+/-32 muK). 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 0.3-sigma_n with that observed by the VSA at 33 GHz, and within 0.2-sigma_n with the Sunyaev-Zel'dovich (SZ) spectrum.
Our analyses show that it is a non-Gaussian feature in the CMB at a level of 4.4-sigma, where sigma accounts for primordial CMB fluctuations, thermal noise and residual radio sources contributions. The probability of finding
such a deviation or larger in simulations including Gaussian CMB is only 0.63 per cent. Therefore, an explanation other than primordial Gaussian 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.
However, from the absence of X-ray emission in this region we conclude that the whole decrement can not be generated solely via the SZ effect in such structure. Therefore, the most plausible scenario is a combination between a negative CMB feature and an SZ effect, probably generated by a warm/hot gas distribution.
These observations confirm the presence of this strong and resolved negative spot at -37+/-5 mJy/beam (-229+/-32 muK). 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 0.3-sigma_n with that observed by the VSA at 33 GHz, and within 0.2-sigma_n with the Sunyaev-Zel'dovich (SZ) spectrum.
Our analyses show that it is a non-Gaussian feature in the CMB at a level of 4.4-sigma, where sigma accounts for primordial CMB fluctuations, thermal noise and residual radio sources contributions. The probability of finding
such a deviation or larger in simulations including Gaussian CMB is only 0.63 per cent. Therefore, an explanation other than primordial Gaussian 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.
However, from the absence of X-ray emission in this region we conclude that the whole decrement can not be generated solely via the SZ effect in such structure. Therefore, the most plausible scenario is a combination between a negative CMB feature and an SZ effect, probably generated by a warm/hot gas distribution.