Constraints on $μ$-distortion fluctuations and primordial non-Gaussianity from Planck data

Abstract

We use the Planck HFI channel maps to make an all sky map of $μ$-distortion fluctuations. Our $μ$-type distortion map is dominated by the $y$-type distortion contamination from the hot gas in the low redshift Universe and we can thus only place upper limits on the $μ$-type distortion fluctuations. For the amplitude of $μ$-type distortions on $10'$ scales we get the limit on root mean square (rms) value $μ_{rms}^{10'}< 6.4\times 10^{-6}$, a limit 14 times stronger than the COBE-FIRAS ($95\%$ confidence) limit on the mean of $< μ> <90\times 10^{-6}$. Using our maps we also place strong upper limits on the auto angular power spectrum of $μ$, $C_{\ell}^{μμ}$ and the cross angular power spectrum of $μ$ with the CMB temperature anisotropies, $C_{\ell}^{μT}$. The strongest observational limits are on the largest scales, $\ell(\ell+1)/(2π)C_{\ell}^{μμ}|_{\ell=2-26}<(2.3\pm 1.0)\times 10^{-12}$ and $\ell(\ell+1)/(2π)C_{\ell}^{μT}|_{\ell=2-26}<(2.6\pm 2.6)\times 10^{-12}~{K}$. Our observational limits can be used to constrain new physics which can create spatially varying energy release in the early Universe between redshifts $5\times 10^4\lesssim z\lesssim 2\times 10^6$. We specifically apply our observational results to constrain the primordial non-Gaussianity of the local type, when the source of $μ$-distortion is Silk damping, for very squeezed configurations with the wavenumber for the short wavelength mode $46 \lesssim k_{S} \lesssim 10^4 ~{Mpc^{-1}}$ and for the long wavelength mode $k_{L}\approx 10^{-3} ~{Mpc^{-1}}$. Our limits on the primordial non-Gaussianity parameters are $f_{NL}<10^5, τ_{NL}<1.4\times 10^{11}$ for $k_{S}/k_{L}\approx 5\times 10^4- 10^7$. We give a new derivation of the evolution of the $μ$-distortion fluctuations. We also introduce mixing of Bose-Einstein spectra and $y^{BE}$-type distortions.