Neutral hydrogen surveys for high-redshift galaxy clusters and protoclusters

Abstract

We discuss the possibility of performing blind surveys to detect large‐scale features of the Universe using 21‐cm emission. Using instruments with ∼5–10 arcmin resolution currently in the planning stage, it should be possible to detect virialized galaxy clusters at intermediate redshifts using the combined emission from their constituent galaxies, as well as less overdense structures, such as protoclusters and the ‘cosmic web’, at higher redshifts. Using semi‐analytic methods, we compute the number of virialized objects and those at turnaround which might be detected by such surveys. We find that there is a surprisingly large number of objects even using small (∼5 per cent) bandwidths and elaborate on some issues pertinent to optimizing the design of the instrument and the survey strategy. The main uncertainty is the fraction of neutral gas relative to the total dark matter within the object. We discuss this issue in the context of the observations which are currently available.

Non-Standard Hierarchies of the Runnings of the Spectral Index in Inflation

“…The relations α s ∝ (n s − 1) 2 and β s ∝ (n s − 1) 3 are characteristic of standard hierarchies and very similar to the predictions of single field slow roll inflation (as n s − 1 ∝ , α s ∝ 2 and so on). Similarly to the expectation of fiducial models of inflation (15), this predicts β s < 0. Overall, this model is largely indistinguishable from the most simplistic versions of inflation and as a result, to achieve consistency with a more certain detection of an alternative hierarchy with β s ≈ O(10 −2 ), this basic realisation of VSL would have to be extended, much like the most basic inflationary scenarios.…”

“…Similarly, future CMB survey missions such as the Cosmic Origins Explorer (CORE) [12,13] or the Polarized Radiation Imaging and Spectroscopy Mission (PRISM) [14], 21 cm mapping [15] with an instrument such as the Square Kilometre Array [16], or a spectroscopic galaxy survey with the Euclid satellite [17] could constrain α s and β s . Particularly with a combination of some or all of these future experiments (or comparable alternatives), as forecasted in [18], the uncertainty in the runnings could be brought down to O(10 −3 ).…”

Cosmology on the Largest Scales with the SKA

“…IM is an alternative approach for probing the density field of the large-scale structure (Battye et al 2004;Wyithe & Loeb 2008;Chang et al 2008;Peterson et al 2009). It involves mapping out the combined emission of the 21 cm, or HI, line from unresolved galaxies.…”

Investigation on the Frequency Allocation for Radio Astronomy at the L Band

“…The initial aim is to observe galaxy clusters for the purpose of learning about their dark matter mass (Battye, Davies, & Weller 2004). We have also started a collaboration with the International Centre for Radio Astronomy Research based in Perth, Australia, in order to be part of the first ever Asia-Oceania interferometer network involving China, Japan, South Korea, Malaysia, and Australia.…”