Abstract
Low-frequency observatories are currently being constructed with the goal of detecting redshifted 21cm emission from the epoch of reionization. These observatories will also be able to detect intensity fluctuations in the cumulative 21cm emission after reionization, from hydrogen in unresolved damped Ly-alpha absorbers (such as gas rich galaxies) down to a redshift z~3.5. The inferred power spectrum of 21cm fluctuations at all redshifts will show acoustic oscillations, whose co-moving 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 percent in a redshift window just prior to the end of the reionization era, provided that foregrounds can be removed over frequency band-passes of >8MHz. 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 one percent 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%) 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 square degrees. Together with other data sets, observations of 21cm fluctuations will allow full coverage of the acoustic scale from the present time out to z~12.
Highlights
Measurement of the fluctuations in the intensity of redshifted 21cm emission from neutral hydrogen promises to be a powerful probe of the reionization era (Furlanetto et al 2006)
Wyithe & Loeb (2007) recently demonstrated that fluctuations in the 21cm emission would remain substantial over a range of epochs following the end of the overlap era owing to the significant fraction by mass of neutral hydrogen that is locked up in the dense pockets that form the damped Lyα absorbers (DLAs) such as gas-rich galaxies
We show that observations of the acoustic scale using 21cm emission could be used to constrain the nature of the dark energy in the unexplored redshift range of 1.5 z 6, as well as during the reionization era, and so would be complementary to galaxy redshift surveys
Summary
Measurement of the fluctuations in the intensity of redshifted 21cm emission from neutral hydrogen promises to be a powerful probe of the reionization era (Furlanetto et al 2006). Wyithe & Loeb (2007) recently demonstrated that fluctuations in the 21cm emission would remain substantial over a range of epochs following the end of the overlap era owing to the significant fraction by mass of neutral hydrogen that is locked up in the dense pockets that form the damped Lyα absorbers (DLAs) such as gas-rich galaxies These systems trace the matter power spectrum on large scales. If the dark energy behaves like a cosmological constant, its effect on the Hubble expansion is dominant only at z 1 and becomes negligible at z 2 In this case studies of the BAO scale at low redshift would provide the most powerful measurement. Unless otherwise specified we adopt the set of cosmological parameters determined by WMAP3 (Spergel et al 2007) for a flat ΛCDM universe
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
