Department of Physics, Harvard University, 17 Oxford Street, Cambridge, Massachusetts 02138, USA.
Phys Rev Lett. 2019 Sep 27;123(13):131301. doi: 10.1103/PhysRevLett.123.131301.
The matter in our Universe comes in two flavors: dark and baryonic. Of these, only the latter couples to photons, giving rise to the well-known baryon acoustic oscillations and, in the process, generating supersonic relative velocities between dark matter and baryons. These velocities-imprinted with the acoustic scale in their genesis-impede the formation of the first stars during cosmic dawn (z∼20), modulating the expected 21-cm signal from this era. In a companion paper we showed, combining numerical simulations and analytic models, that this modulation takes the form of robust velocity-induced acoustic oscillations (VAOs), with a well-understood shape that is frozen at recombination, and unaffected by the unknown astrophysics of star formation. Here we propose using these VAOs as a standard ruler at cosmic dawn. We find that three years of 21-cm power-spectrum data from the upcoming HERA interferometer should be able to measure the Hubble expansion rate H(z) at z=15-20 to percent-level precision, ranging from 0.3% to 11% depending on the strength of astrophysical feedback processes and foregrounds. This would provide a new handle on the expansion rate of our Universe during an otherwise unprobed epoch, opening a window to the mysterious cosmic-dawn era.
暗物质和重子物质。其中，只有后者与光子相互作用，产生了众所周知的重子声学振荡，并在此过程中产生了暗物质和重子之间的超音速相对速度。这些在起源时带有声速标度的速度会阻碍宇宙黎明（z∼20）期间第一批恒星的形成，从而调节了这个时期预期的 21 厘米信号。在一篇相关的论文中，我们结合数值模拟和分析模型表明，这种调制表现为稳健的速度诱导声振荡（VAO），其形状可以很好地理解，在重组合时被冻结，并且不受未知的恒星形成天体物理的影响。在这里，我们提议将这些 VAO 用作宇宙黎明的标准标尺。我们发现，即将到来的 HERA 干涉仪的三年 21 厘米功率谱数据应该能够以百分之一的精度测量 z=15-20 处的哈勃膨胀率 H(z)，具体范围取决于天体物理反馈过程和前景的强度，从 0.3%到 11%不等。这将为在 otherwise unprobed 时期宇宙的膨胀率提供一个新的处理方法，为神秘的宇宙黎明时代打开一扇窗口。
