Baryonic acoustic oscillations in 21-cm emission: a probe of dark energy out to high redshifts

Abstract

Low‐frequency observatories are currently being constructed with the goal of detecting redshifted 21‐cm emission from the epoch of reionization. These observatories will also be able to detect intensity fluctuations in the cumulative 21‐cm emission after reionization, from hydrogen in unresolved damped Lyα absorbers (such as gas‐rich galaxies) down to a redshift z∼ 3.5. The inferred power spectrum of 21‐cm fluctuations at all redshifts will show acoustic oscillations, whose comoving scale can be used as a standard ruler to infer the evolution of the equation of state for the dark energy. We find that the first generation of low‐frequency experiments (such as MWA or LOFAR) will be able to constrain the acoustic scale to within a few per cent in a redshift window just prior to the end of the reionization era, provided that foregrounds can be removed over frequency bandpasses of ≳8 MHz. This sensitivity to the acoustic scale is comparable to the best current measurements from galaxy redshift surveys, but at much higher redshifts. Future extensions of the first‐generation experiments (involving an order of magnitude increase in the antennae number of the MWA) could reach sensitivities below 1 per cent in several redshift windows and could be used to study the dark energy in the unexplored redshift regime of 3.5 ≲z≲ 12. Moreover, new experiments with antennae designed to operate at higher frequencies would allow precision measurements (≲1 per cent) of the acoustic peak to be made at more moderate redshifts (1.5 ≲z≲ 3.5), where they would be competitive with ambitious spectroscopic galaxy surveys covering more than 1000 deg2. Together with other data sets, observations of 21‐cm fluctuations will allow full coverage of the acoustic scale from the present time out to z∼ 12.

Observational probes of cosmic acceleration

“…A different concept is that of 21 cm intensity mapping (Peterson et al, 2006;Ansari et al, 2008;Chang et al, 2008;Loeb and Wyithe, 2008;Wyithe et al, 2008;Seo et al, 2010a). Here one does not identify individual galaxies but instead measures the combined emission of the 21 cm line from all galaxies in a volume of order 10 Mpc on a side.…”

Reionization and Cosmology with 21-cm Fluctuations

“…In addition to precision dark energy constraints, an SKA HI survey would provide a wealth of astrophysical data about galaxy formation and evolution. Wyithe, Loeb & Geil (2008), Chang et al (2008) and Peterson, Bandura & Pen (2006) realized that compact interferometers with wide fields-of-view might be able to perform cosmological measurements, particularly those associated with the BAO scale, at a fraction of the SKA's cost. These proposed instruments have low angular resolution-they cannot resolve individual galaxies-and have been tuned to have the highest sensitivity at BAO angular scales (∼150 cMpc).…”

21 cm observation of large-scale structures atz ~ 1

“…Radio observation of the 21 cm emission of neutral hydrogen is a very promising technique for mapping matter distribution up to redshift z ∼ 3, and it complements optical surveys, especially in the optical redshift desert range 1 z 2, and possibly up to the reionization redshift (Wyithe et al 2008).…”