Scientists propose new ways to uncover the universe’s first generation of galaxies and dark matter

In the early morning of July 7, the international academic journal Nature Astronomy published online a major result of the collaborative research between the National Astronomical Observatory of the Chinese Academy of Sciences and Northeastern University. The theoretical study proposes that using one-dimensional power spectroscopic measurements of 21-centimeter forest signals at the dawn of the universe, future Square Kilometer Array radio telescopes (SKAs) will be able to simultaneously unravel the nature of the universe’s first generation galaxies and dark matter.

Xu Yidong, associate researcher of the National Astronomical Observatory of the Chinese Academy of Sciences, Chen Xuelei, researcher and Zhang Xin, professor of Northeastern University, are co-corresponding authors of the paper.

How did the first generation of galaxies in the universe form? How do they illuminate the Dark Ages and usher in the dawn of the universe? How was the intergalactic medium of the early universe ionized and heated by the first generation of galaxies? These questions have always been the major scientific problems that the field of astronomy is committed to answering. The 21 cm spectral line of neutral hydrogen provides a unique means of detection of the cosmic dawn and the first generation of galaxies, and the detection of the cosmic dawn and reionization using the 21 cm spectral line is one of the most important scientific goals of the Square Kilometer Array Radio Telescope (SKA).

The 21 cm signal of neutral hydrogen has several observation modes. A common observation mode is a 21 cm signal measurement with cosmic microwave background radiation as the background source. At the same time, various structures in the early universe and the gases of hydrogen atoms around them would produce dense 21 cm absorption lines on the spectrum of high redshift radio point sources, which are figuratively called 21 cm forests. Due to the weak signal and dependence on the acquisition of radio bright sources at the dawn of the universe, 21 cm forest detection has faced great challenges for many years. On the other hand, the 21-centimeter forest signal is affected by both the heating effect of the first generation of galaxies and the properties of dark matter, and it is difficult to distinguish between these two effects in observation, making it difficult for the 21-cm forest probe to actually be used to limit the thermal effects or dark matter properties of the first generation of galaxies in the more than two decades since it was proposed.

According to the researchers, this work delved into the 21-centimeter forest probe, which was rarely discussed in the past, and proposed an original statistical measurement scheme that can not only limit the nature of the first generation of galaxies in the universe, but also measure the mass of dark matter particles at the same time.

In recent years, a number of quasars with high redshift radio noise have been discovered, and the SKA telescope has entered the engineering construction stage, and 21 cm forest observations are imminent.

“We realize that signal changes caused by the warm and dark matter effect and the heating effect have different scale distribution characteristics on the spectrum, so through one-dimensional power spectrum analysis, key features will be statistically extracted to distinguish the two effects.” Xu Yidong said, “Moreover, if two measurements of the same spectrum are cross-correlated, the noise can be significantly reduced, thereby improving the signal-to-noise ratio.” This is critical for the extraction of this weak signal in a 21 cm forest. ”

The simulation results show that the one-dimensional cross-power spectrum measurement significantly improves the sensitivity of observation, and the amplitude and shape characteristics of the one-dimensional power spectrum make the scale dependence of the signal visible. This makes it feasible to make a 21-centimeter forest feasible and be able to measure both the mass of dark matter particles and the thermal history of the dawn of the universe. Therefore, the one-dimensional power spectrum of the 21-centimeter forest can indeed be a cosmological probe with one stone, providing a promising new way to unravel the mystery of dark matter and the first generation of galaxies.

Professor Katherine Mack, an internationally renowned expert and from the Canadian Institute of Perimeter Theoretical Physics, commented in Nature Astronomy: “This study proposes an interesting method to use a 21-cm forest power spectrum to limit two phenomena simultaneously: the heating of cosmic X-rays on the intergalactic medium and the possible effects of warm dark matter. While previous studies have examined the possibility of a 21-centimeter forest as a probe of the intergalactic medium, including the warm dark matter effect as a separate signal provides a new scientific goal for future observations. ”

The editorial team of Nature Astronomy also commented on the study: “The farthest reaches of our universe are always extremely mysterious, difficult to observe directly because they are blocked by dust, light-absorbing atoms and gases in intermediate media. This study turns absorption into an advantage, using it to break the decentralization of different effects encountered by other methods, and can be used to elucidate the structural formation of the early universe. ”

Experts believe that the development of this breakthrough method is of great significance for unlocking the mystery of dark matter and the formation of early celestial bodies in the universe, which will further advance our understanding of dark matter and reveal the process of the formation and evolution of the structure of the universe. Through deeper observations and analysis, scientists are expected to gain more insights into the nature of dark matter and early galaxy formation in the near future, further expanding our understanding of the universe.

This research was supported by the National Key Research and Development Program of China and the National Natural Science Foundation of China. (Source: China Science News Gan Xiao)

Research diagram (Courtesy of National Astronomical Observatory)

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