IAU PhD prize awarded to Yi Zhang

Former MPE PhD student honored for her outstanding dissertation

The International Astronomical Union (IAU) has awarded former MPE PhD student Yi Zhang with a PhD prize for her thesis on “Hot Circumgalactic Medium in the eROSITA All-Sky Survey”. Along with the other prizewinners, she will give a talk at the next IAU general assembly, taking place at the Auditorium Parco della Musica in Rome in August 2027. Another MPE researcher received a “honourable mention” for his PhD Thesis. 

During her PhD, Yi Zhang focused on analyzing data from the eROSITA telescope to study the faint X-ray emission from the hot circumgalactic medium (CGM). The CGM, a diffuse halo of gas surrounding galaxies like our Milky Way, plays a critical role in galaxy evolution. Its hot phase, characterized by temperatures of millions of degrees, is notoriously difficult to observe due to its faint and extended X-ray signature. However, this phase is believed to hold the majority of baryons surrounding galaxies and contains crucial information about galaxy formation, feedback processes, and quenching mechanisms.

Using data from the eROSITA All-Sky Survey, combined with large galaxy samples from the Sloan Digital Sky Survey (SDSS) and the Dark Energy Spectroscopic Instrument (DESI) Legacy Survey, Yi Zhang employed advanced stacking and modeling techniques to detect this elusive X-ray emission around Milky Way-mass and more massive galaxies. Her thesis meticulously measured X-ray surface-brightness profiles, correlated X-ray luminosity with galaxy properties (stellar mass, halo mass), compared emission around star-forming and quiescent galaxies, and estimated the mass of the hot gas. These findings provide essential new observational constraints for understanding the evolution of galaxies.

Yi Zhang's supervisors for her PhD thesis were Kirpal Nandra (official supervisor) and Gabriele Ponti (scientific supervisor). She also acknowledges the close supervision and guidance provided by Johan Comparat and Andrea Merloni.

Another MPE scientist is honoured by the IAU

“I feel truly honored that my thesis has received this prize,” says Yi Zhang. “This work would not have been possible without the remarkable X-ray dataset provided by the eROSITA telescope, and I am grateful for the support, discussions, and encouragement from my supervisors and the High Energy group.”

In december 2025, Yi Zhang left MPE and took a position as a postdoc at the Max Planck Institute for Astrophysics (MPA), where she focuses on X-ray data analysis, simulations for future X-ray telescopes, and exploring multiwavelength surveys.

Yi Zhang is the second person from MPE who received the IAU PhD Prize in Division D. In 2021, Riccardo Arcodia, former PhD student in the high-energy group and meanwhile BHI Fellow at the Black Hole Initiative at Harvard University, was awarded the IAU PhD Prize for his thesis “Accretion onto Black Holes Across the Mass Scale”.

In addition, Ruancun Li, a postdoc in the infrared group at MPE, received a honorable mention by the IAU PhD Prize comittee for his PhD thesis “Spectral Energy Distribution of Active Galactic Nuclei”. In his thesis, which he finished in China, Li made a seminal analysis of the time-evolving, optical+UV+X-ray spectrum of a prominent AGN that delivered empirical determinations of the mass accretion rate for a supermassive black hole. He joined MPE in September 2025 and is working on quasars and AGN using the GRAVITY+ Instrument.

About the IAU PhD Prize

The IAU PhD Prize recognises the outstanding scientific achievements of astronomy PhD students worldwide. Each of the IAU’s nine Divisions awards a prize to the candidate it identifies as having carried out the most remarkable work in the previous year, with the nine Divisions agreeing to jointly award an extra prize, the IAU PhD Prize-at-large. 
Each PhD prize winner will receive airfare, registration fee, and accommodation to attend the IAU General Assembly. Certificates will be awarded at Division Days, where, at the discretion of the Division, prize recipients may have an opportunity to present their thesis work.

The IAU is the international astronomical organisation that brings together more than 12 000 professional astronomers from more than 100 countries. Its mission is to promote and safeguard the science of astronomy in all its aspects through international cooperation. The IAU also serves as the internationally recognised authority for assigning designations to celestial bodies and the surface features on them. Founded in 1919, the IAU is the world's largest professional body for astronomers.