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CGM/IGM around high-z galaxies
How does gas in and around galaxies fuel their growth?
We combine quasar absorption spectroscopy with JWST, ALMA, MUSE etc multiwavelength observations to identify and characterize the galaxies associated with absorbing gas. Our studies of the first complete neutral-carbon-selected absorbers revealed metal-rich, molecular environments with disturbed gas motions (Ledoux+15; Zou+18; Noterdaeme+18). Using Mg II absorbers, we investigate how cool halo gas evolves and connects to star formation and galaxy environments (Zou+21; Zou+24a; Zou+24b). Our recent results suggest that extended cold gas may fuel early disk formation and redistribute metals and dust, linking halo gas to galaxy assembly (Zou+25).
First star signature at high-z
Can we uncover the chemical signatures of the first stars?
We search for gas and galaxies show distinctive abundance patterns in high-redshift gas, complemented by JWST observations to identify the galaxies associated with its enrichment. We discovered a carbon-enhanced absorber whose chemical composition resembles that of carbon-enhanced metal-poor stars, offering a possible fossil record of early stellar enrichment (Zou+20; Zou+26b in prep). Near the end of reionization, we also find carbon- and oxygen-enhanced absorbers whose abundance patterns may indicate enrichment by a top-heavy stellar population, potentially including Population III stars (Zou+24b). By connecting these chemical fingerprints to nearby galaxies, we investigate how the first stellar populations enriched their surroundings.
Early galaxy assembly and dust formation
How do dusty galaxies assemble in the early Universe? We combine JWST spectroscopy and infrared imaging with ALMA observations to connect obscured star formation, galaxy interactions, and environment. In COSMOS-3D, we studied 18 dusty galaxies or candidates at z = 4.9–7.2, finding that merging systems occupy the strongest compact overdensities, while MIRI-bright galaxies show evidence for an additional hot-dust component without an excess of nearby visible Hα-emitting companions. These results suggest that merger-driven growth and hot-dust activity may trace distinct phases of early galaxy assembly, rather than occurring simultaneously at the centers of forming structures (Zou+26; Geng, Zou+26 in prep).
AGN and host galaxies
How do gas and dust shape black hole growth and its connection to host galaxies? We combine JWST spectroscopy and imaging with X-ray observations to investigate AGN obscuration, outflows, and host-galaxy properties. In COSMOS-3D, we identified two AGNs at z ∼ 3 with dense gas traced by He I absorption and hot dust detected by MIRI. One is an X-ray-detected AGN with an LRD-like spectral energy distribution, while the other shows strong outflows exceeding 5,000 km s⁻¹. Modeling places the absorbing gas on broad-line-region scales. These findings link LRD-like sources to X-ray AGNs, suggesting that dense nuclear gas may regulate obscuration across different black hole growth phases (Li, Zou+26).
Local galaxy clusters
How does feedback reshape hot gas in galaxy groups and clusters?
We use X-ray observations to investigate how processes beyond gravitational heating affect the intracluster medium. Using Chandra observations of 23 nearby galaxy groups and low-mass clusters, we measured their X-ray luminosity–temperature relation while carefully accounting for selection biases. We found no clear break in the relation between galaxy groups and massive clusters, providing a consistent picture across halo masses. These measurements establish a robust benchmark for testing how feedback changes the hot-gas properties of galaxy groups (Zou+16).