The reporter learned from the National Astronomical Observatories of China of the Chinese Academy of Sciences that in the early morning of July 7, 2023 (Beijing time), the international academic journal Nature Astronomy published online a scientific research achievement of cooperation between the National Astronomical Observatories of China and Northeast University. This theoretical research proposes that the future square kilometer array Radio telescope (SKA) will be able to reveal the properties of the first generation galaxy and dark matter of the universe at the same time by using the one-dimensional power spectrum measurement of the 21 cm forest signal at the dawn of the 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. How did the first generation galaxies in the universe form? How do they illuminate the Dark Ages and usher in the dawn of the universe? How did the early intergalactic media in the universe be ionized and heated by the first generation of galaxies? These questions have always been major scientific challenges that the field of astronomy is committed to solving. The 21cm spectral line of neutral hydrogen provides a unique means of detecting the cosmic dawn and the first generation of galaxies. Using the 21cm spectral line to detect the cosmic dawn and Reionization is also one of the most important scientific goals of the square kilometer array Radio telescope (SKA). There are multiple observation modes for the 21 centimeter signal of neutral hydrogen. The common observation mode is 21 cm signal measurement with Cosmic microwave background radiation as the background source. At the same time, various structures in the early universe and their surrounding hydrogen atomic gases would generate dense 21 centimeter absorption lines in the spectrum of high redshift radio point sources, which 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, 21 centimeter forest exploration 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, making it difficult for the 21 centimeter forest detection to be actually used to limit the thermal effect or the properties of dark matter of the first generation galaxy in the more than 20 years since 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. In recent years, a number of Quasar with high redshift radio noise have been found, and the SKA telescope has entered the engineering construction stage, so it is urgent to carry out 21 cm forest observation. "We realize that the signal changes caused by the Warm dark matter effect and the heating effect have different scale distribution characteristics in the spectrum, so through one-dimensional power spectrum analysis, we can statistically extract key features to distinguish the two effects." Xu Yidong said, Moreover, if cross correlation is performed between two measurements of the same spectrum segment, it will significantly reduce noise, thereby improving signal-to-noise ratio. This is crucial for extracting weak signals such as 21 cm forests. Simulation results show that one-dimensional cross power spectrum measurement significantly improves the sensitivity of observation, while the amplitude and shape characteristics of the one-dimensional power spectrum reveal the scale dependence of the signal. This makes 21 centimeter forests feasible and can be measured simultaneously
Edit：XiaoWanNing Responsible editor：YingLing
Source：CCTV NEWS
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