Standard Ruler at Cosmic Dawn

Area of Science:

• Cosmology
• Astrophysics
• Early Universe Physics

Background:

• The Universe contains dark matter and baryonic matter, with only baryons interacting with photons.
• Baryon acoustic oscillations (BAOs) arise from photon-baryon coupling, creating supersonic relative velocities between dark matter and baryons.
• These velocities imprint the acoustic scale, hindering early star formation and modulating the 21-cm signal during cosmic dawn (z~20).

Purpose of the Study:

• To propose using velocity-induced acoustic oscillations (VAOs) as a standard ruler to probe cosmic dawn.
• To determine the precision of measuring the Hubble expansion rate H(z) at z=15-20 using VAOs.

Main Methods:

• Utilizing numerical simulations and analytic models to understand VAO characteristics.
• Analyzing the 21-cm power spectrum data from the upcoming HERA interferometer.
• Combining simulation results with observational data to constrain cosmological parameters.

Main Results:

• VAOs possess a well-defined shape, frozen at recombination and independent of star formation astrophysics.
• Three years of HERA data can measure H(z) at z=15-20 with percent-level precision (0.3%-11%).
• Measurement precision depends on astrophysical feedback strength and foreground contamination.

Conclusions:

• VAOs offer a novel standard ruler for cosmic dawn studies.
• This method provides a new way to measure the Universe's expansion rate during an unprobed epoch.
• The findings open a new observational window into the mysterious cosmic-dawn era.