Dr. Zhen-Yi CAI （蔡振翼，Zin-Iak CUA）

Schematic diagram of the history of the Universe. The Universe is in a neutral state at 400 thousands years after the Big Bang and light from the first generation stars starts to ionize the hydrogen. After several hundred million years, the gas in the Universe is completely ionized. Credit. NAOJ

Credit. NAOJ

Our Group & Collaborations

I have been closely collaborating with Prof. Jun-Xian Wang (USTC) on AGN variability and Prof. Gianfranco De Zotti (INAF/Padova) on Galaxy Formation, and more, such as Profs. Yong-Quan Xue (USTC), Wei-Min Gu (XMU), Mou-Yuan Sun (XMU), and Shan-Shan Weng (NJNU) in AGNs/BHXRBs, and Xu Kong (USTC), Guan-Wen Fang (AQNU), and Andrea Lapi (SISSA/Trieste) in Galaxies.

My major interests and Representative works

Students

  • • AGN Spectral Energy Distribution (SED)

 

  • ◦ In the extreme ultraviolet, average quasar SEDs are independent of luminosity and redder than all previous mean composite quasar spectra (2023, Nature Astronomy, 7, 1506).
  • ◦ Being independent of more physical properties, such as black hole mass and Eddington ratio, the universality of the average quasar SED exists since cosmic noon (2024, Universe, 10, 431; here are supplementary materials).

 

  • • AGN Variability

 

  • ◦ EUCLIA: a new thermal fluctuation model indicating a novel mechanism for the inter-band continuum lags for AGN, rather than the light echoing (2018, ApJ, 855, 117), successfully explains a broad phenomena of AGN variability, including the multi-wavelength correlation and the puzzling large UV to X-ray lags (2020, ApJ, 892, 63).
  • ◦ New clues between jet launching and disk fluctuation: the inner disks in radio loud quasars may be more stable (2019, SCPMA, 62, 69511), verified observationally (2024, ApJ, 971, 60).
  • ◦ New optimized statistical method for measuring unbiased variation properties of AGN: a minimal baseline of ~ 8 times the intrinsic variation timescale for achieving a 2% accuracy in measured timescale (2024, ApJ, 961, 5).

 

  • • Intergalactic medium


  • • Cosmic H/He Reionization: relative role of galaxies and AGN


 

  • ◦ Progenitors of early-type elliptical galaxies and massive bulges of Sa galaxies, i.e., proto-spheroids at z > 1.5, are forming stars in a self-regulated way, rather than galaxy merging (2013, ApJ, 768, 21).
  • ◦ Dust extinction is a key ingredient of understanding the cosmic evolution of Lyman break galaxies and Lyα emitters, and galaxies are the dominant ionizing source for the cosmic hydrogen reionization (2014, ApJ, 785, 65).
  • ◦ Part of the excess of z > 4 sub-millimeter galaxies can be understood in terms of an initial mass function (IMF) somewhat top-heavier than Chabrier, but not the extreme top-heavy IMFs commonly assumed in the galaxy merging model (2020, ApJ, 891, 74).
  • ◦ Our model prediction without any adjustment of the parameters was verified by dusty star-forming galaxies detected by the South Pole Telescope, and a similar IMF is suggested for star formations across cosmic time (2022, ApJ, 932, 13).
  • • PhD
    • ◦ Mr. Zhen-Bo Su (2023-; 2 papers published; co-supervised with Prof. Jun-Xian Wang)
    • ◦ Mr. Min-Xuan Cai (2023-; 1 paper published; co-supervised with Prof. Lu-Lu Fan)
    • ◦ Dr. Mr. Wen-Yong Kang (2019-2022; co-supervised with Prof. Jun-Xian Wang; USTC博后)
    • ◦ Dr. Mr. Fei-Fan Zhu (2015-2019; co-supervised with Prof. Jun-Xian Wang; 中电三十二所)
  • • MS
    • ◦ Mr. Jie Li (2022-)
    • ◦ Mr. Zhen-Bo Su (2021-2022; 转博)
  • • BS
    • ◦ Mr. Zhan-Shuo Liu (2024-; 大研)
    • ◦ Mr. Zi-Rui Zhang (2024-; 毕设)
    • ◦ Mr. Jin-Chao Cai (2023-2024; 毕设)
    • ◦ Mr. Jia-Ming Zhu-Ge & Wen-He Lv (2022-2023; 大创, 获评校级优秀项目; USTC读研)
    • ◦ Mr. Xu-Fan Hu (2021-2023; 大创+毕设, 1 paper published; 上海交通大学李政道研究所读研)
    • ◦ Mr. Zhen-Bo Su (2020-2021; 毕设; co-supervised with Prof. Yang Huang from YNU; USTC读研)
    • ◦ Mr. Hao Zhai (2020-2021; 毕设; co-supervised with Prof. Jun-Xian Wang; 新加坡管理大学读研)