The CIB-lensing bispectrum: impact on primordial non-Gaussianity and detectability for the Planck mission

Abstract

We characterize the Cosmic Infrared Background (CIB)-lensing bispectrum which is one of the contributions to the three-point functions of Cosmic Microwave Background (CMB) maps in harmonic space. We show that the CIB-lensing bispectrum has a considerable strength and that it can be detected with high significance in the Planck high-frequency maps. We also present forecasts of the contamination on different shapes of the primordial non-Gaussianity f nl parameter produced by the CIB-lensing bispectrum and by the extragalactic point sources bispectrum in the Planck high-resolution CMB anisotropy maps. The local, equilateral and orthogonal shapes are considered for 'raw' single-frequency (i.e., without applying any component separation technique) and foreground-reduced Planck temperature maps. The CIB-lensing correlation seems to mainly affect orthogonal shapes of the bispectrum -with ∆f (ort) nl = −21 and −88 for the 143 and 217 GHz bands respectively -while point sources mostly impact equilateral shapes, with ∆f (eq) nl = 160, 54 and 60 at 100, 143 and 217 GHz. However, the results indicate that these contaminants do not induce any relevant bias on Planck f nl estimates when foreground-reduced maps are considered: using SEVEM for the component separation we obtain ∆f (ort) nl = 10.5 due to the CIB-lensing and ∆f (eq) nl = 30.4 due to point sources, corresponding to 0.3σ and 0.45σ in terms of the Planck 2013 f nl uncertainty. The component separation technique is, in fact, able to partially clean the extragalactic source contamination and the bias is reduced for all the shapes. We have further developed single-and multiple-frequency estimators based on the Komatsu, Spergel & Wandelt (2005) formalism that can be implemented to efficiently detect this signal.

Cosmic infrared background anisotropies as a window into primordial non-Gaussianity

“…In particular, by taking the correlation matrix R νν ′ independent of the angular scale, we are supposing that the shape of dust residual power spectra are the same over all the frequencies. This is something expected and supported by simulations of component separation performance (Curto et al 2016).…”

“…To test this, we have compared the large-scale power spectra obtained with different CIB models, all providing a good fit to the Planck data. Besides the extended halo model used in this paper, we have considered: 1) a linear model where the 2-halo contribution is determined by an effective bias and by the star formation history, which in turn are constrained by Planck data (see §5.4 of Planck Collaboration XXX 2014); 2) a simplified halo model in which all galaxies have the same luminosity regardless of their host dark matter halo used, e.g.. in Planck Collaboration XVIII (2011); Curto et al (2015). Although they agree at ℓ > ∼ 200, the power spectra Figure 9).…”

Planck2015 results

“…However, the amplitude of the CIB bispectrum is predicted to be small in the cleaned Planck maps and it has actually not been detected (see Table 3). The CIB-lensing bispectrum signal is frequency dependent, and it is mostly dominant in the very high Planck frequencies (see e.g., Curto et al 2015).…”

Foreground biases on primordial non-Gaussianity measurements from the CMB temperature bispectrum: Implications forPlanckand beyond

“…To our knowledge, the ISW-related biases presented here have not been computed elsewhere, with the exception of the ISW-lensing bias. Other biases involving CMB lensing have received some attention, albeit limited [29,30]. In general, f loc NL biases are generated in the CMB temperature field by bispectra involving the ISW effect, CMB lensing, the cosmic infrared background (CIB), and the thermal (tSZ) and kinematic Sunyaev-Zel'dovich (kSZ) effects.…”