Anomalies in the low CMB multipoles and extended foregrounds

Abstract

We discuss how an extended foreground of the cosmic microwave background (CMB) can account for the anomalies in the low multipoles of the CMB anisotropies. The distortion needed to account for the anomalies is consistent with a cold spot with the spatial geometry of the local supercluster (LSC) and a temperature quadrupole of order $\ensuremath{\Delta}{T}_{2}^{2}\ensuremath{\approx}50\text{ }\text{ }\ensuremath{\mu}{K}^{2}$. If this hypothetic foreground is subtracted from the CMB data, the amplitude of the quadrupole ($\ensuremath{\ell}=2$) is substantially increased, and the statistically improbable alignment of the quadrupole with the octopole ($\ensuremath{\ell}=3$) is substantially weakened, increasing dramatically the likelihood of the cleaned maps. By placing the foreground on random locations and then computing the likelihood of the cleaned maps we can estimate the most likely place for this foreground. Although the 1-year WMAP data clearly points the location of this hypothetical foreground to the LSC or its specular image (i.e., the vicinity of the poles of the cosmic dipole axis), the three-year data seems to point to these locations as well as the north ecliptic pole. We show that this is consistent with the symmetries of the cosmic quadrupole. We also discuss a possible mechanism that could have generated this foreground: the thermal Sunyaev-Zeldovich effect caused by hot electrons in the LSC. We argue that the temperature and density of the hot gas which are necessary to generate such an effect, though in the upper end of the expected range of values, are marginally consistent with present observations of the X-ray background of spectral distortions of the CMB.