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NAOC Scientists Make a Further Step towards Understanding Dark Energy

Jul 20, 2020

The extended Baryon Oscillation Spectroscopic Survey (eBOSS) collaboration released a batch of latest scientific results in over 20 papers on July 20 (Beijing Time).These results include two studies on dark energy, led by Profs. ZHAO Gongbo and WANG Yuting from the National Astronomical Observatories of the Chinese Academy of Sciences (NAOC), respectively.

Based on the eBOSS observations, Prof. ZHAO's team successfully measured the history of the cosmic expansion and structure growth in a huge volume in the past universe, corresponding to a distance range between 0.7 and 1.8 billion light years away from us. This volume was never probed before (Fig. 1). 

This study took advantage of a method called "multi-tracer analysis", which could mitigate the observational systematics proposed and implemented by Prof. ZHAO and Prof. WANG. 

"This work detected the existence of dark energy at a significance of 11 s, which is the strongest evidence ever on dark energy from galaxy surveys," said Prof. ZHAO. "The eBOSS observations are consistent with the dynamical dark energy probed by our team using the BOSS survey 3 years ago." 

One of the biggest challenges of cosmological implications of galaxy surveys is data analysis, especially in developing new methods to improve the statistical accuracy and mitigate the systematics. eBOSS, as the first galaxy survey that observes multiple types of galaxies in a vast cosmic volume, makes it possible for a multi-tracer analysis. 

"Cross-correlating multiple types of galaxies is an efficient way to reduce statistical uncertainties, with observational systematics mitigated at the same time, which is key to obtaining robust cosmological results," said Prof. WANG. 

ZHANG Weibing, a graduate student at NAOC, is involved in this project by building a theoretical template for cosmological analysis. "I'm so happy that my theory work is recognized by the community." 

Dark energy is dominating the current universe, so it is vitally important to reveal its nature. The eBOSS collaboration, which consists of over 30 top research institutes on astronomy around the world including NAOC, was formed for tackling the problem of dark energy. Operating since 2014, eBOSS has taken over 1 million spectra in the redshift range of 0.6<z<2.2, and made a series of milestones in cosmology. 

Although eBOSS has completed its mission, it is a starting point of the next chapter. The experience with eBOSS is valuable for cosmology with larger galaxy surveys, including the Chinese Space Station Telescope (CSST), Dark Energy Spectroscopic Instrument (DESI) and Prime Focus Spectrograph (PFS). 

The papers from NAOC can be accessed at https://arxiv.org/abs/2007.09010 and https://arxiv.org/abs/2007.09011.

This work is supported by Natural Science Foundation of China, Ministry of Science and Technology of China, and Chinese Academy of Sciences. 

Fig. 1. The exploration of the Universe by the SDSS mission during the past two decades (1998-2019) (Image by eBOSS collaboration) 

Contact

XU Ang

National Astronomical Observatories of China

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