Multipole expansion for H i intensity mapping experiments: simulations and modelling

Abstract

We present a framework and an open-source python toolkit to analyse the two-point statistics of 3D fluctuations in the context of H i intensity maps using the multipole expansion formalism. We include simulations of the cosmological H i signal using N-body and lognormal methods, foregrounds and their removal, as well as instrumental effects. Using these simulations and analytical modelling, we investigate the impact of foreground cleaning and the instrumental beam on the power spectrum multipoles as well as on the Fourier space clustering wedges. We find that both the instrumental beam and the foreground removal can produce a quadrupole (and a hexadecapole) signal, and demonstrate the importance of controlling and accurately modelling these effects for precision radio cosmology. We conclude that these effects can be modelled with reasonable accuracy using our multipole expansion technique. We also perform a Markov Chain Monte Carlo (MCMC) analysis to showcase the effect of foreground cleaning on the estimation of the H i abundance and bias parameters. The accompanying python toolkit is available at https://github.com/IntensityTools/MultipoleExpansion, and includes an interactive suite of examples to aid new users.

The HI intensity mapping bispectrum including observational effects

“…the H bias. Also, including higher order multipoles in this analysis would extend upon (Cunnington et al 2020b) which studied IM observational effects in the power spectrum multipoles. IM observational effects should also leak signal into higher-ℓ thus it would be revealing to see if including higher-order multipoles improves parameter constraints for the H IM bispectrum, as has been shown to be the case for the power spectrum (Soares et al 2021).…”

“…To test our models, we select a low-redshift simulation snapshot at 𝑧 = 0.39 which is the approximate central redshift for a MeerKAT-like survey performed in the L-band (899 < 𝜈 < 1184 MHz, or equivalently 0.2 < 𝑧 < 0.58) (Santos et al 2017;Pourtsidou 2018). We outline the details for the simulations in Appendix A1 and also refer the reader to Cunnington et al (2020a); Soares et al (2021); Cunnington et al (2020b) where similar simulations were used. The final simulated data are over-temperature maps 𝛿𝑇 H (𝒙, 𝑧) = 𝑇 H (𝒙, 𝑧) − 𝑇 H (𝑧), where 𝑇 H (𝑧) represents the mean temperature of the field, and these are shown in Figure 1.…”

“…As a useful data-compression technique, and similar to the multipole expansion of the power spectrum into Legendre polynomials (see Cunnington et al (2020b); Soares et al (2021) for applications to H IM), the dependence on the orientation of a triangle of wavevectors, parameterised by 𝜔 and 𝜙, can be decomposed into spherical harmonics (Scoccimarro et al 1999;Scoccimarro 2015)…”

Baryon acoustic oscillations from HI intensity mapping: the importance of cross-correlations in the monopole and quadrupole

“…As expected, the number of null or below 3σ detections increases with redshift: this is due to a decreasing SNR, as discussed in the related Appendix B2 and shown in Figure 5 shows how the BAO features in the quadrupole (right panel) appear more robust with respect to the damping effects from the beam if compared with the monopole Hi auto-correlation (left panel). The different response of the higher-order multipoles to intensity mapping observational effects has been previously studied (Blake 2019;Cunnington et al 2020a) and this behaviour could mean that higherorder multipoles are of crucial importance to parameter constraints: more details about these features are included in the Appendix C.…”

The BINGO Project VI: HI Halo Occupation Distribution and Mock Building

“…Therefore, a larger box size simulation like ELUCID with high particle resolution can provide better statistics about the Hi halo occupation distribution in very massive clusters. The 21-cm intensity mapping using a semi-analytical model galaxy catalog from MDPL2 simulation has been considered (Cunnington et al 2020). However the MDPL2 simulation can only resolve halos with mass > 3 × 10 10 M /h (Klypin et al 2016), one order of magnitude larger than the ELUCID simulation.…”