Sal Wanying Fu
I am a PD Soros and NSF graduate research fellow, and an astronomy PhD candidate at UC Berkeley. Advised by Prof. Dan Weisz, I study the resolved stellar populations of the smallest galaxies in the universe using primarily Hubble Space Telescope. Before coming to UC Berkeley, I completed multiple stellar spectroscopy projects with Dr. Josh Simon at the Carnegie Observatories, and earned my B.A. in physics at Pomona College. I am interested in everything that falls under the umbrella of near-field cosmology: leveraging observations of ancient objects in our cosmic neighborhood to understand how our universe came to be.
Current Research
Resolved stellar metallicity measurements provide a key way of quantifying the gastrophysics driving the evolution of a galaxy, but have been previously prohibitive to obtain in distant yet scientifically interesting dwarf galaxies by state-of-the-art ground-based spectroscopy on 10m-class telescopes. For my thesis, I have published hundreds of novel stellar metallicity measurements in Local Group dwarf galaxies across a variety of environments and masses. These measurements were made using a novel application of HST imaging, targeting the metallicity sensitive Calcium II H & K lines using the F395N filter. This measurement technique enables further sampling down the galaxy's luminosity function and have vastly expanded the sample of available stellar metallicities in our target galaxies.
Using narrow-band imaging from HST proposal GO-15901 (PI: Weisz), I have published novel stellar metallicity distribution functions (MDFs) in 13 Milky Way ultra-faint dwarf galaxies. The MDF of Eri II, the brightest galaxy analyzed among this subset, has been used to infer a star formation history characterized by high levels of gas outflow compared to its more massive counterparts, which may be caused by strong feedback and a shallower dark matter halo potential.
I have also been awarded 23 orbits on HST in Cycle 28 (Program GO-16226) to conduct the same observations on two quenched field dwarf galaxies in the Local Group, Cetus and Tucana. This program has contributed 374 stellar metallicity measurements in the Tucana dSph, where there were previously there were 52 from ground-based stellar spectroscopy. This dataset has enabled us to see the enrichment picture of this galaxy in unprecedented detail: 1) A detailed shape of its stellar MDF, 2) A metallicityy gradient measurement of high fidelity to compare more robustly against simulations, and 3) Multiple metallicity populations as evidenced by the two respective branches of its split RGB.
My recent paper, applying this same technique to two faint M31 satellites from HST Program GO-16226 (PI: Weisz), is also now on the arXiv and submitted to ApJ. With HST, we measure nearly 300 new stellar metallicities across these two galaxies where spectroscopy previously yielded 13. These measurements enable detailed views into the shape of their MDFs, and characterization of their metallicity gradients.
Forthcoming work includes interpreting dwarf galaxy MDFs across these different environments to characterize the gastrophysics of their star formation.
Publications
- S. W. Fu, D. R. Weisz, et al. 2024. Stellar Metallicities and Gradients in the Faint M31 Satellites Andromeda XVI and Andromeda XXVIII. ApJ, 975, 2. https://ui.adsabs.harvard.edu/abs/2024ApJ...975....2F/abstract
- S. W. Fu, D. R. Weisz, et al. 2024. Stellar Metallicities and Gradients in the Isolated, Quenched Low-mass Galaxy Tucana. ApJ, 965, 36. https://ui.adsabs.harvard.edu/abs/2024ApJ...965...36F/abstract
- N. R. Sandford, ... S. W. Fu 2024. Strong outflows and inefficient star formation in the reionization-era ultrafaint dwarf galaxy Eridanus II. MNRAS, 530, 2, 2314. https://ui.adsabs.harvard.edu/abs/2024MNRAS.530.2315S/abstract
- S. W. Fu, D. R. Weisz, et al. 2023. Metallicity Distribution Functions of 13 Ultra-faint Dwarf Galaxy Candidates from Hubble Space Telescope Narrowband Imaging. ApJ, 958, 167. https://ui.adsabs.harvard.edu/abs/2023ApJ...958..167F/abstract
- S. W. Fu, D. R. Weisz, et al. 2022. Metallicity Distribution Function of the Eridanus II Ultra-faint Dwarf Galaxy from Hubble Space Telescope Narrowband Imaging. ApJ, 925, 6. https://ui.adsabs.harvard.edu/abs/2022ApJ...925....6F/abstract
- S. W. Fu, J. D. Simon, et al. 2019. Dynamical Histories of the Crater II and Hercules Dwarf Galaxies. ApJ, 883, 11. https://ui.adsabs.harvard.edu/abs/2019ApJ...883...11F/abstract
- S. W. Fu, J. D. Simon, et al. 2018. The Origin of the 300 km/s Stream Near Segue 1. ApJ, 866, 42. https://ui.adsabs.harvard.edu/abs/2018ApJ...866...42F/abstract
Contact Me
You can reach me via email at swfu at berkeley dot edu.