Abstract
The initial conditions for the density perturbations in the early Universe, which dictate the large-scale structure and distribution of galaxies we see today, are set during inflation. Measurements of primordial non-Gaussianity are crucial for distinguishing between different inflationary models. Current measurements of the matter power spectrum from the cosmic microwave background only constrain this on scales up to k ∼ 0.1 Mpc-1. Reaching smaller angular scales (higher values of k) can provide new constraints on non-Gaussianity. A powerful way to do this is by measuring the HI matter power spectrum at [Formula: see text]. In this paper, we investigate what values of k can be reached for the Low-Frequency Array (LOFAR), which can achieve [Formula: see text]1″ resolution at approximately 50 MHz. Combining this with a technique to isolate the spectrally smooth foregrounds to a wedge in [Formula: see text]-k⊥ space, we demonstrate what values of k we can feasibly reach within observational constraints. We find that LOFAR is approximately five orders of magnitude away from the desired sensitivity, for 10 years of integration time. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades'.
Highlights
The end of Inflation set the density fluctuations which dictated the growth of large-scale structure and the distribution of galaxies we see today
The LOw Frequency ARray (LOFAR) is a phased array comprised of fixed dipoles, with phase delays introduced into the signal paths to electronically ‘point’ the telescope
In this paper we have considered the question of probing the small-scale 21 cm power spectrum from the Dark Ages, using LOFAR, which is the only currently operational telescope capable of reaching sub-arcsecond scales at the relevant low frequencies
Summary
The end of Inflation set the density fluctuations which dictated the growth of large-scale structure and the distribution of galaxies we see today. Angular resolution offers more than just foreground isolation: it allows us to probe higher values of k⊥, which is crucial for extracting new information from the data to place constraints on the 21 cm power spectrum [17,18]. It is interesting to ask the question whether LOFAR could be used to detect the small-scale 21 cm power spectrum, which is the focus of this speculative study. We intend this to be informative only, with an eye towards the future construction of a low-frequency lunar array. Throughout this paper we have assumed cosmological parameters from the Planck 2013 results [23]
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