Chinese astronomers have proposed a "two birds with one arrow" cosmological probe to explore the Dawn Galaxy | Universe | China
How did the first generation of galaxies in the universe form? How do they illuminate the dark age and usher in the dawn of the universe? These questions have always been major scientific challenges that the field of astronomy is dedicated to solving. In the early morning of July 7, 2023 (Beijing time), the international academic journal Nature Astronomy published an important achievement of the cooperative research between the National Astronomical Observatory of the Chinese Academy of Sciences and Northeastern University online. Researchers have found that using the one-dimensional power spectrum of the "21 centimeter forest" signal during the dawn of the universe, future square kilometer array radio telescopes will be able to simultaneously reveal the properties of the first generation galaxies and dark matter in the universe.
The 21 centimeter spectral line of neutral hydrogen provides a unique detection method for the dawn of the universe and the first generation galaxies. The common observation mode is the 21 centimeter signal measurement using cosmic microwave background radiation as the background source. In the early universe, various structures and their surrounding hydrogen atomic gases would generate dense 21 centimeter absorption lines in the spectrum of high redshift radio point sources. These absorption line clusters are vividly referred to as "21 centimeter forests.". Due to weak signals and reliance on the acquisition of radio bright sources during the dawn of the universe, the detection of the "21 centimeter forest" has faced great challenges for many years. On the other hand, the "21 centimeter forest" signal is influenced by both the heating effect of the first generation galaxy and the properties of dark matter, making it difficult to distinguish between these two effects in observations. This makes it difficult for the "21 centimeter forest" detection to be practically used to limit the thermal effects or properties of dark matter in the first generation galaxy for more than 20 years after its proposal.
This work delves into the previously rarely discussed "21 centimeter forest" probe and proposes an original statistical measurement scheme that not only limits the properties of the first generation galaxies in the universe, but also simultaneously measures the mass of dark matter particles.
Using a 21 centimeter spectral line to detect dawn in the universe is one of the most important scientific goals of the square kilometer array radio telescope, and the square kilometer array radio telescope has also entered the engineering construction stage. It is urgent to carry out "21 centimeter forest" observation. The simulation results show that the one-dimensional cross power spectrum measurement of the "21 centimeter forest" significantly improves the sensitivity of the observation. At the same time, the amplitude and shape characteristics of the one-dimensional power spectrum reveal the scale dependence of the signal. This makes "21 centimeter forest" feasible and allows for simultaneous measurement of dark matter particle mass and thermal history during the dawn of the universe. Therefore, the one-dimensional power spectrum of the "21 centimeter forest" can indeed serve as a cosmological probe for "killing two birds with one arrow", providing a highly promising new way to unravel the mysteries of dark matter and first generation galaxies.
The editorial team of Nature Astronomy commented on this study: "The farthest part of our universe is always extremely mysterious, difficult to observe directly due to being blocked by dust, light absorbing atoms, and gases in the intermediate medium. This study transforms absorption into an advantage, using it to break the degeneracy of different effects encountered by other methods and can be used to elucidate the structural formation of the early universe."
Associate Researcher Xu Yidong from the National Astronomical Observatory of the Chinese Academy of Sciences, Researcher Chen Xuelei, and Professor Zhang Xin from Northeastern University are the co corresponding authors of the paper.