Planck intermediate results. LVI. Detection of the CMB dipole through modulation of the thermal Sunyaev-Zeldovich effect: Eppur si muove II

TLDR: In this paper, the authors present the first detection of the thermal Sunyaev-Zeldovich (tSZ) effect in the tSZ maps and find that it is consistent with direct measurements of the CMB dipole.

Abstract: The largest temperature anisotropy in the cosmic microwave background (CMB) is the dipole, which has been measured with increasing accuracy for more than three decades, particularly with the Planck satellite. The simplest interpretation of the dipole is that it is due to our motion with respect to the rest frame of the CMB. Since current CMB experiments infer temperature anisotropies from angular intensity variations, the dipole modulates the temperature anisotropies with the same frequency dependence as the thermal Sunyaev-Zeldovich (tSZ) effect. We present the first, and significant, detection of this signal in the tSZ maps and find that it is consistent with direct measurements of the CMB dipole, as expected. The signal contributes power in the tSZ maps, which is modulated in a quadrupolar pattern, and we estimate its contribution to the tSZ bispectrum, noting that it contributes negligible noise to the bispectrum at relevant scales.

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Table 1. Values of χ2 (with Nd.o.f. = 3) under the assumption of no dipolar modulation term (“No dipole”), and assuming the presence of the dipolar modulation term (“With dipole”) for the 2D-ILC CMB template map.

Fig. C.1. As in Fig. 4, but with `max = 2750 compared to `max = 1411 used in the paper. If we were to trust the y map out to these multipoles, then these results would have a significance of >12σ.

Fig. B.1. As in Figs. 3 (top) and 4 (bottom), except using the NILC y maps. Top panels: results from the map-space method, bottom panels: those from the harmonic-space method.

Fig. 2. Posteriors for the CMB dipole parameters using the map-space analysis (top) and harmonic-space analysis (bottom). The left panels use the SMICA-NOSZ CMB maps, whereas the right use the 2D-ILC CMB maps. MILCA y map results are shown in orange, and 2D-ILC y map results are shown in blue. Black dashed lines show the best-fit parameters from direct measurements of the CMB dipole. Dark and light contours enclose 68% and 95%, respectively. Titles for each panel give the best-fit results, along with the 68% uncertainties.

Fig. A.2. Absolute (left) and relative (right) difference between the bispectrum with and without the dipole-modulation term.

Fig. A.1. Binned bispectrum, for simulated y maps, with `max = 500 and bin sizes of 10, and “scalemaps” defined in Eq. (A.4), of Nside = 512. Left panels: bispectrum for a simulated y map with the dipole modulation; right panels: same with no dipole-modulation. The quantities P, F, and S are as defined in Eq. (A.13).