Can the Local Supercluster explain the low CMB multipoles

We show that the thermal Sunyaev-Zeldovich effect caused by hot electrons in the Local Supercluster (LSC) can explain the abnormal quadrupole and octopole of the cosmic microwave background (CMB) that were measured by WMAP and COBE. The distortion needed t

a r X i v :a s t r o -p h /0312124v 3 22 D e c 2003astro-ph/0312124

Can the Local Supercluster explain the low CMB multipoles?

L.Raul Abramo ∗

Instituto de F´ısica,Universidade de S˜a o Paulo

CP 66318,05315-970S˜a o Paulo,Brazil

Laerte Sodr´e Jr.†

Instituto Astronˆo mico e Geof´ısico,

Universidade de S˜a o Paulo

CP 3386,01060-970S˜a o Paulo,Brazil

(Dated:February 2,2008)

We show that the thermal Sunyaev-Zeldovich effect caused by hot electrons in the Local Superclus-ter (LSC)can explain the abnormal quadrupole and octopole of the cosmic microwave background (CMB)that were measured by WMAP and COBE.The distortion needed to account for the low observed quadrupole is a spot in the direction of the LSC with a temperature decrease of order ∆T ≈−7µK for ν∼20—90Ghz photons.The temperature and density of the hot gas which can generate such an effect are consistent with observations of the X-ray background.If this hypo-thetic foreground is subtracted from the WMAP data,we find that the amplitude of the quadrupole (ℓ=2)is substantially increased,and that the “planarity”of both the quadrupole and the octopole (ℓ=3)are weakened.For smaller scales the effect decays and,at least in our simplified model,it does not affect the angular power spectrum at ℓ>10.Moreover,since the Sunyaev-Zeldovich effect increases the temperature of photons with frequencies above 218GHz,observations sensitive in that range (such as PLANCK’s HFI)will be able to confirm whether the LSC indeed affects the CMB.PACS numbers:98.80.-k,98.65.Dx,98.70.Vc,98.80.Es

Introduction The cosmic microwave background (CMB)anisotropies have now been measured with exquisite accuracy by WMAP [1].Such a barrage of new data seldom brings only confirmation of known theories and mechanisms,and WMAP is no exception:early reion-ization [1],lack of higher correlations [2]and a curious supression of power at the largest observable scales [3,4]are some of the most intriguing questions that have been raised by the WMAP data.In this letter we focus on the problem of the CMB multipoles corresponding to the largest scales,and show that at least these anomalies can be explained by ordinary physics.

The CMB temperature anisotropies on very large

scales were first measured by COBE [6].WMAP [1]con-

firmed those observations and showed moreover a nearly

flat curve of the angular power spectrum C ℓat large

scales (spherical harmonic indices ℓ<100)and a pattern

of acoustic oscillations at smaller scales (ℓ>150).This is

consistent with the inflationary picture of a nearly-scale

invariant spectrum of adiabatic density perturbations.

However,the data is not entirely devoid of its quirks:

there are a few “sticky”points in the observed angu-

lar power spectrum,in particular those around ℓ=200,

ℓ=40and ℓ=20,all with statistically significant devi-

ations from the expected (smooth)curve.In addition to

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