Yongda Zhu

Research interests:
intergalactic medium, reionization, galaxy formation & evolution

This background image (from simulations) shows the distribution of gas in the Universe, and each light spot has the size of a galaxy!
read more about this image | (Bolton et al. 2017)

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About me

I recently joined Steward Observatory (University of Arizona) as a postdoctoral researcher under the guidance of Prof. Marcia Rieke and Prof. George Rieke. Before joining Steward, I was working on intergalactic medium (IGM) and cosmic reionization with Prof. George Becker at University of California, Riverside.
You can find my CV here. My research has been focused on when and how the neutral hydrogen gas filling between galaxies became ionized around one billion years after the Big Bang using Keck, VLT, and ALMA. Currently, I am studying the evolution of galaxies at high-redshift using JWST.

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photo: © ESO/ John Colosimo

IGM during the Epoch of Reionization

Reionization is one of the most important "phase transitions" in the history of our Universe. Revealing when and how reionization occurred is essential to the understanding of dark matter, the formation and evolution of the first stars and galaxies, as well as super massive black holes. Large-scale fluctuations in intergalactic Lyman-$\alpha$ opacity at $z \leq 6$ suggest that reionization may have ended later than is normally assumed. Alternatively, this can be explained by a post-reionization fluctuating UV background. Now I am trying to use spectra of high-redshift QSOs to probe the IGM along the lines of sight and distinguish these models.

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Publications

All publications: NASA/ADS
Paper online materials: Zhu et al. 2021 (dark gaps) | Zhu et al. 2022a (Lyman-beta) | Zhu et al. 2022b (Milky Way)

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Dark gaps in the Ly$\beta$ forest

- Constraints on the neutral hydrogen fraction during the Epoch of Reionization from dark gaps in the Ly$\beta$ forest (Zhu et al. 2022). The new results are based on the largest sample of high-redshift QSOs with Ly$\beta$ coverage.

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The mean free path

- Direct measurements of the ionizing photon mean free path over redshift 5-6 (Zhu et al. 2023). Such a rapid evolution in the mean free path provides robust evidence that reionization is not complete at $z \sim 6$.

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Public Outreach & Services

- Virtual Stargazing: increasing the accessibility of science for the gerneral public during the pandemic.
- Camp Highlander: I was an astronomy instructor for K-12 students. Courses developed: Multi-wavelength Universe, Gravity Similator. Please email me for course materials if you are intersted!
- Riverside Science and Engineering Fair: helping students improve their STEM projects by providing feedback.

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Public Outreach & Services

- Stargazing event at Home Gardens Academy, Corona, CA. Over 100 students and parents attended the event.

Talks & News
Talk ELT Science in Light of JWST, UCLA Dec 11-15, 2023
Talk Galaxy Group Seminar, University of Michigan Nov 9, 2023
Talk Special Kashiwa-Mitaka Meeting (KMM) Seminar, University of Tokyo Aug 22, 2023
Link Reionisation in the Summer Conference @ MPIA June 26-30, 2023
- Friday Lunch Time Astrophysics Seminar @ UCSC Nov 4, 2022
- Astro Lunch Talk @ UCLA Oct 4, 2022
- Astro Lunch Talk @ UC Santa Barbara Sep 28, 2022
- Reionization on a Blackboard workshop Sep 19-22, 2022
- talk @ UC Davis arXiv Coffee Meeting May 25, 2022
Program talk @ UCR PASS May 25, 2022
- talk @ Tsinghua High-z team Apr 16, 2022
Berkeley BCCP Reionization Workshop Mar 21-23, 2022
Link European Astronomical Society Annual Meeting Jun 28-Jul 02, 2021
Live record Summer All Zoom Epoch of Reionization Astronomy Conference Jun 14-Jun 17, 2021

Email

yongdaz [at] arizona.edu

Address

Steward Observatory,
933 N Cherry Ave, Tucson, AZ 85721

Office

IR Wing