[{"content":" Observations We observe galaxies and molecular gas across cosmic time.\nALMA JWST Local Universe High-z Galaxies Ziyi Guo Galactic Chemical Evolution I connect ALMA and JWST observations with chemical evolution models to understand how galaxies form stars, enrich their gas, and build the elements over cosmic time. Research Publications CV Theory We build models that translate chemical fingerprints into galaxy histories.\nStar\nFormation Stellar\nYields Chemical\nEnrichment Outflow Research Highlights CO isotopologues as IMF tracers Using ¹³CO/C¹⁸O ratios from ALMA to probe IMF variations in high-redshift main-sequence and starburst galaxies.\nLearn more Physically motivated GCE models Connecting stellar yields, star formation histories, gas inflow and outflow, and abundance patterns in galaxies.\nLearn more From local galaxies to cosmic dawn Combining ALMA and JWST measurements to interpret early star formation, metallicity, and chemical enrichment.\nLearn more Research Themes 1. Observations ALMA and JWST measurements of molecular lines, isotopes, and chemical abundances in galaxies.\n2. Chemical Fingerprints Isotopes and elements trace stellar populations, gas conditions, and recent star formation histories.\n3. GCE Modeling Models connect stellar yields, SFH, inflow, outflow, and abundance evolution across galaxy types.\n4. IMF \u0026 Stellar Yields Constraining the IMF and nucleosynthesis from massive, binary, AGB, and low-metallicity stars.\n5. Galaxy Evolution Understanding how galaxies assemble their mass, metals, and stellar populations over cosmic time.\n“The elements we observe today are the memory of galaxies.\nMy goal is to read that memory.” ","date":"25 June 2026","externalUrl":null,"permalink":"/","section":"","summary":"","title":"","type":"page"},{"content":"Open full CV PDF\nContact # Ph.D. candidate, Nanjing University ORCID: 0000-0002-7532-1496 Email: zyguo@smail.nju.edu.cn, zyguo.astro@gmail.com GitHub: GuoZiYi-astro Education # Nanjing University, Ph.D. student, School of Astronomy \u0026amp; Space Science\n2022-present\nNanjing University, Master student, School of Astronomy \u0026amp; Space Science\n2020-2022\nShandong University, BSc., School of Physics\n2016-2020\nResearch Interests # High-redshift galaxies ALMA observations and molecular-line data analysis Galactic chemical evolution IMF variations and stellar yields JWST abundance constraints in the early Universe Technical Skills # Programming: Python Astronomical software: CASA, NuPyCEE Languages: Chinese, English Awards # Tiangong Scholarship\n2024\nInstitute for Nuclear Astrophysics of China Award for Young Scientist\n2023, for an outstanding presentation at the Pre-Workshop of the 3rd International Workshop on Origin of Elements and Cosmic Evolution.\n","date":"25 June 2026","externalUrl":null,"permalink":"/cv/","section":"","summary":"","title":"CV","type":"page"},{"content":"","date":"25 June 2026","externalUrl":null,"permalink":"/outreach/","section":"","summary":"","title":"Outreach","type":"page"},{"content":" First-Author Papers # Limited imprint of high-mass IMF variations on sodium abundances in main-sequence galaxies\nAstronomy \u0026amp; Astrophysics, accepted.\nZiyi Guo, Donatella Romano, Zhiqiang Yan, Zhi-Yu Zhang, Xiaoting Fu, Lizhi Xie, Tereza Jerabkova, Gabriella De Lucia, Michaela Hirschmann, Fabio Fontanot, Eda Gjergo, Alice Concas, Xiaodong Tang.\nFirst detection of CO isotopologues in a high-redshift main-sequence galaxy: evidence of a top-heavy stellar initial mass function\nThe Astrophysical Journal, 2024-08.\nZiyi Guo, Zhi-Yu Zhang, Zhiqiang Yan, Eda Gjergo, Rob Ivison, Allison Man, Xiaoting Fu, Yong Shi.\nCo-Authored Papers # Massive Star Formation at Supersolar Metallicities: Constraints on the Initial Mass Function\nResearch in Astronomy and Astrophysics, 2026-02.\nEda Gjergo, Zhi-Yu Zhang, Pavel Kroupa, Aleksei Sorokin, Zhiqiang Yan, Ziyi Guo, Tereza Jerabkova, Akram Hasani Zonoozi, Hosein Haghi.\nStellar population astrophysics (SPA) with the TNG. The phosphorus abundance on the young side of Milky Way\nMonthly Notices of the Royal Astronomical Society, 2026-01.\nMingjie Jian, Xiaoting Fu, Valentina D\u0026rsquo;Orazi, Angela Bragaglia, S. Bijavara Seshashayana, He Zhao, Ziyi Guo, Karin Lind, Noriyuki Matsunaga, Antonino Nunnari, Giuseppe Bono, Nicoletta Sanna, Donatella Romano, Marina Dal Ponte.\nA SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): Impact of Galaxies on the Circumgalactic Medium Metal Enrichment at z \u0026gt; 6 Using the JWST and VLT\nThe Astrophysical Journal Letters, 2024-03.\nSiwei Zou, Zheng Cai, Feige Wang, Xiaohui Fan, Jaclyn B. Champagne, Joseph F. Hennawi, Jan-Torge Schindler, Emanuele Paolo Farina, Jinyi Yang, Kohei Inayoshi, Eduardo Banados, Sarah E. I. Bosman, Zihao Li, Xiaojing Lin, Yunjing Wu, Fengwu Sun, Ziyi Guo, and collaborators.\nAlpha-enhanced astrochemistry: the carbon cycle in extreme galactic conditions\nMonthly Notices of the Royal Astronomical Society, 2024-01.\nThomas G. Bisbas, Zhi-Yu Zhang, Eda Gjergo, Ying-He Zhao, Gan Luo, Donghui Quan, Xue-Jian Jiang, Yichen Sun, Theodoros Topkaras, Di Li, Ziyi Guo.\nProperties of Dense Molecular Gas along the Major Axis of M82\nThe Astrophysical Journal, 2022-07-01.\nFei Li, Zhi-Yu Zhang, Junzhi Wang, Feng Gao, Shanghuo Li, Jing Zhou, Yichen Sun, Ziyi Guo, Shu Liu.\nIn Preparation # 13CO/C18O in high-redshift starburst galaxies\nAn expanded ALMA and archival ALMA/VLA sample of CO isotopologue measurements in high-redshift starburst galaxies, extending previous work on molecular isotopologues and top-heavy IMFs.\n","date":"25 June 2026","externalUrl":null,"permalink":"/publications/","section":"","summary":"","title":"Publications","type":"page"},{"content":"My research focuses on galactic chemical evolution: how galaxies form stars, cycle gas, and build up the chemical elements across cosmic time. I combine ALMA and JWST observations with chemical evolution models to connect molecular lines and elemental abundances with star formation histories, stellar yields, gas inflow and outflow, and possible variations in the stellar initial mass function.\nCO Isotopologues as IMF Tracers # The stellar initial mass function (IMF) is fundamental to how we infer star formation rates, stellar masses, feedback, and galaxy evolution. In my PhD work, I use the 13CO/C18O isotopologue ratio as a tracer of IMF variations in high-redshift galaxies. The physical motivation is that most 13C is produced by low- and intermediate-mass stars, while much of 18O is produced by massive stars. Their abundance ratio therefore carries information about the stellar populations that enriched a galaxy.\nWith sensitive ALMA observations and careful data reduction, I recovered weak CO isotopologue emission in strongly lensed galaxies at cosmic noon. In a high-redshift main-sequence galaxy, I detected 13CO and C18O and measured a low isotopologue flux ratio, providing evidence for a more top-heavy IMF than in local main-sequence systems. This result was published in The Astrophysical Journal in 2024.\nI am extending this work to a larger sample of high-redshift starburst galaxies using new ALMA observations and archival ALMA/VLA data. The goal is to test whether low 13CO/C18O ratios are common in intense star-forming environments and to connect these ratios with the evolutionary stage of starbursts.\nGalactic Chemical Evolution Models # Chemical abundances are shaped by many processes at once: the IMF, stellar yields, star formation histories, gas accretion, outflows, stellar mass growth, and galaxy assembly. I use galactic chemical evolution (GCE) models to turn these coupled processes into testable predictions for observed abundance patterns.\nDuring my PhD, I worked extensively with the open-source GCE code NuPyCEE and developed model frameworks that combine traditional chemical evolution assumptions with more realistic star formation histories from semi-analytical galaxy formation models. One project tests whether sodium can trace high-mass IMF variations in main-sequence galaxies. The result, accepted by Astronomy \u0026amp; Astrophysics, shows that sodium abundances in these systems have only a limited imprint of high-mass IMF variations, while also establishing a flexible framework for testing other elements.\nStellar Yields and Chemical Fingerprints # I am interested in improving the physical realism of GCE models through more complete stellar yield prescriptions. This includes massive stars, AGB stars, very massive stars, low-metallicity populations, and binary evolution. Because binary interactions are common but often simplified in galaxy-scale chemical evolution studies, incorporating their yields is an important next step for interpreting abundance patterns in the early Universe.\nThese models can help identify which elements or isotopes are most sensitive to the IMF, which trace star formation histories, and which preserve information about extreme stellar populations.\nJWST, Cosmic Dawn, and Early Enrichment # JWST has opened a new window on galaxies in the early Universe, revealing strong carbon and nitrogen enrichment, high circumgalactic metallicities, very blue UV spectra, and luminous nebular emission in young systems. I aim to test whether these observations can be explained by top-heavy IMFs, extremely metal-poor stars, and enrichment channels such as hypernovae, pair-instability supernovae, and rapidly rotating stars.\nBy combining JWST abundance measurements with ALMA molecular-line constraints and GCE modeling, I hope to build a coherent picture of how the first generations of galaxies enriched their gas and formed stars.\nStarburst Timescales # My future work also uses 13CO/C18O together with star formation rates as a potential clock for starburst evolution. GCE models predict that the isotopologue ratio changes rapidly during the early stages of a burst before settling to a lower equilibrium value. Comparing these predictions with nearby systems and high-redshift starbursts can help constrain when intense star formation was triggered and how quickly it reshapes a galaxy\u0026rsquo;s chemical state.\n","date":"25 June 2026","externalUrl":null,"permalink":"/research/","section":"","summary":"","title":"Research","type":"page"},{"content":" Selected Talks # Exploring the Evolution of CNOPS Elements from Earth and Space\nSexten Center for Astrophysics, 2026. Talk: 13C/18O as an IMF tracer in high-redshift galaxies.\nGalaxy Formation in the Cosmic Web: Bridging Simulations and Observations\nThe 12th Sino-German Meeting, 2025. Talk: IMF in the high-redshift Universe - CO isotopologue ratios reveal the IMF in high-redshift galaxies.\nAstronomy Talk\nINAF, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, 2024. Talk: First detection of CO isotopologues in a high-redshift main-sequence galaxy.\nCosmic Threads: Interlinking the Stellar Initial Mass Function from Star-birth to Galaxies\nSexten Center for Astrophysics \u0026ldquo;Riccardo Giacconi\u0026rdquo;, 2024. Talk: Evidence of a top-heavy stellar initial mass function from high-redshift CO isotopologues.\nThe 3rd International Workshop on Origin of Elements and Cosmic Evolution\nBeihang University, International Research Institute for Multidisciplinary Science, Institute of Nuclear Astrophysics of China, and COSNAP, 2023. Talk: From stellar yield to evolution of the Universe - the first detection of CO isotopologues in a high-redshift main-sequence galaxy.\nNearby and Distant Star Formation Conference\nYunnan Observatories, Chinese Academy of Sciences, 2023. Talk: First detection of CO isotopologues in a high-redshift main-sequence galaxy.\nSeminar\nTsinghua University, 2023. Talk: The first detection of CO isotopologues in a high-redshift main-sequence galaxy.\nGravitational Lensing Spring Conference\nBeijing Normal University, 2023. Talk: Constraining the initial mass function in main-sequence galaxies at z ~ 2.\n","date":"25 June 2026","externalUrl":null,"permalink":"/talks/","section":"","summary":"","title":"Talks","type":"page"},{"content":"I am a PhD candidate at Nanjing University working on galactic chemical evolution, with hands-on experience reducing and analyzing ALMA observations. My research connects molecular-line measurements, elemental abundances, stellar yields, and galaxy evolution models to understand how galaxies form stars and enrich their interstellar medium.\nMy current work focuses on using CO isotopologues, especially ¹³CO and C¹⁸O, as tracers of the stellar initial mass function in high-redshift galaxies. Because ¹³C and ¹⁸O are produced by different stellar populations, their abundance and line ratios can preserve information about the stellar populations that enriched a galaxy. I use ALMA observations and galactic chemical evolution models to interpret these chemical fingerprints.\nI am also interested in building more physically motivated chemical evolution frameworks. This includes connecting GCE models with realistic star formation histories, gas inflow and outflow, semi-analytical galaxy formation models, and updated stellar yield prescriptions for massive stars, AGB stars, low-metallicity populations, and binaries.\nLooking ahead, I aim to combine ALMA and JWST observations with chemical evolution modeling and simulations to study star formation, IMF variations, and chemical enrichment from nearby galaxies to the early Universe.\n","date":"25 June 2026","externalUrl":null,"permalink":"/about/","section":"","summary":"","title":"About","type":"page"},{"content":"","externalUrl":null,"permalink":"/authors/","section":"Authors","summary":"","title":"Authors","type":"authors"},{"content":"","externalUrl":null,"permalink":"/categories/","section":"Categories","summary":"","title":"Categories","type":"categories"},{"content":"","externalUrl":null,"permalink":"/series/","section":"Series","summary":"","title":"Series","type":"series"},{"content":"","externalUrl":null,"permalink":"/tags/","section":"Tags","summary":"","title":"Tags","type":"tags"}]