Research
1. Probing galaxy formation and gas in high-redshift cosmic web node
Galaxies are not isolated islands in the Universe: They form and evolve inside large-scale environments, which involve dark matter and flows of gas (CGM/IGM). Observing and analyzing the formation of high-redshift galaxies in environments with special characteristics can deliver a long-awaited opportunity for us to (a) understand what roles the environmental characteristics play in early galaxy formation and (b) conduct a ``stress test’’ to galaxy formation models.
My postdocal research is largely focused on a unique quasar field, MQN01, which hosts a node of cosmic web at z=3.2.footnotes a & b This field also features high concentration of galaxies, massive black holes, and the gas inside and around galaxies.
Early & fast disk formation in the cosmic web: We recently discovered a surprisingly large disk in this cosmic web node using JWST. It has an effective radius of around 10 kpc, as large as the Milky Way nowadays (!). The existence of such a giant disk when the Universe was merely 2 Gyr old indicates that the cosmic web node hosts favorable conditions for disks to form early and fast. These conditions include non-destructive mergers and highly efficient & coherent cosmic gas accretion (Wang et al. 2024).
More results about this special cosmic web node field will be reported soon, which involve quiescent galaxies and the CGM/IGM gas emission.
f.n. a: yes z=3.2 still counts as high-z :-)
f.n. b: seriously speaking, numbers very often give you more illusions than physical insights.
2. “Slitlet-Stepping”: a novel mode of spatially-resolved spectroscopic observations with JWST
I have been involved in a study to develop a novel observing mode for the JWST NIRSpec instrument. The mode, ‘‘Slitlet-Stepping’’, will enable spatially resolved spectroscopic observations of at least 30 galaxies simultaneously, by making use of the Mirco-Shutter Assembly on the NIRSpec. The mode is at least 10 times as efficient as the NIRSpec IFU mode which only targets at one galaxy at a single time. The high efficiency will open up great opportunities for large galaxy surveys with JWST in the near future.
I co-led an effort to implement this mode to the observations of our JWST program, one of the largest GO programs in Cycle 1 for galaxy science.
3. Galactic winds beyond the local universe
Galactic winds are the outflowing gas ejected from galaxies. They are considered to have a prominent impact on galaxy formation especially in the early Universe. However, much has yet to be known regarding the origins and physical properties of these winds.
My thesis research was motivated by one question: How and where do galactic winds occur within galaxies in the early Universe? I aim at answering the question using the spectroscopic data from a Keck observing program, HALO7D (PI: R. Guhathakurta, UC Santa Cruz), which includes around 200 $z \sim 1$ star-forming galaxies with deep exposures by the DEep Imaging Multi-Object Spectrograph (DEIMOS).
Spatially extended galaxy star formation drives winds: I led a case study of the cool phase of galactic winds from a massive star-forming galaxy at $z \sim 1$ (Wang et al. 2022). Our study indicates that the winds are most likely launched from a spatially extended area which includes both the inner and outer regions of the galaxy. We also find that spatially extended star formation is the most probable driver of the observed extended winds. It might be common for the massive star-forming galaxies at $z \gtrsim 1$ to have winds launched from the entire galaxies. This is supported by a separate study, in which we find that spatially extended star formation is common among massive star-forming galaxies at $z \sim 1$ (Wang et al. 2017).
4. The dust attenuation law for galaxies at $z\sim 1$
Accurate measurements of the galaxy star formation rates are essential for us to understand how galaxies form. However, a significant fraction of the star formation can be obscured by dust. The obscured star formation needs to be inferred indirectly by assuming a certain dust attenuation law if no far-infrared photometry is available, which is often the case for the galaxies observed at high redshifts.
Dust law varies with galaxy inclination: In Wang et al. (2018), we find that the dust attenuation law is dependent on the galaxy inclination, which can lead to systematic errors up to 0.3 dex in the inferred star formation rates. By introducing an inclination correction, our study brings more accurate measurements of star formation rates at $z\sim 1$ and above. Details about this study can be found from my talk at the STScI/JHU Galaxy Journal Club.