Constraining primordial non-Gaussianity by combining next-generation galaxy and 21 cm intensity mapping surveys

Abstract

Surveys of the matter distribution contain ‘fossil’ information on possible non-Gaussianity that is generated in the primordial Universe. This primordial signal survives only on the largest scales where cosmic variance is strongest. By combining different surveys in a multi-tracer approach, we can suppress the cosmic variance and significantly improve the precision on the level of primordial non-Gaussianity. We consider a combination of an optical galaxy survey, like the recently initiated DESI survey, together with a new and very different type of survey, a 21 cm intensity mapping survey, like the upcoming SKAO survey. A Fisher forecast of the precision on the local primordial non-Gaussianity parameter $$f_{\textrm{NL}}$$ f NL , shows that this multi-tracer combination, together with non-overlap single-tracer information, can deliver precision comparable to that from the CMB. Taking account of the largest systematic, i.e. foreground contamination in intensity mapping, we find that $$\sigma (f_{\textrm{NL}}) \sim 4$$ σ ( f NL ) ∼ 4 .

Learning to concentrate: multi-tracer forecasts on local primordial non-Gaussianity with machine-learned bias

“…LSS surveys promise to supersede this sensitivity in the near-term [8][9][10][11][12][13][14]. In particular, the multi-tracer technique [13][14][15][16][17][18][19][20][21][22] provides a powerful tool for using large-scale modes most affected by survey sample variance. The presence of local PNG modulates the halo density field in a scale-dependent manner [23,24].…”

Multi-tracer power spectra and bispectra: formalism

“…In the multi-tracer framework (e.g. [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]) we consider the combined information of all correlations of different tracer samples in a given redshift bin and sky patch. The multi-tracer power spectra and bispectra are…”

“…A multi-tracer analysis is particularly effective for constraints on local PNG and other quantities that have a signal on very large scales, where cosmic variance is strongest (see e.g. [29][30][31][32][33][34][35][36][37][38][39][40][41]).…”

Radio-optical synergies at high redshift to constrain primordial non-Gaussianity

“…Foregrounds mostly affect the largest radial scales, where they cannot be separated from the cosmological signal. We decide to treat this effect with a foreground avoidance approach [60,[69][70][71], considering two different methods. The first one consists in applying an exponential suppression factor to the power spectrum in order to remove the radial modes k ∥ = µ k smaller than a critical scale k ∥fg .…”