Dynamics of ultra-diffuse galaxy pairs
I am analyzing spectra of six ultra-diffuse galaxy candidates from the SMUDGes catalog, observed with the Binospec integral field unit on the 6.5 m MMT, to study the dynamics of ultra-diffuse galaxy pairs.
I developed a pipeline that measures their redshifts from emission and absorption lines, with sky-residual masking, continuum subtraction and Gaussian profile fitting. Narrow-band maps and optimized spectral extraction apertures reduce the uncertainties of the measured redshifts.
This work is in progress.
Velocity dispersions of Milky Way satellites
I investigated how to measure intrinsic velocity dispersions, and how to set reliable upper limits, in Milky Way satellite galaxies that have only small samples of stellar radial velocities.
I reanalyzed Keck/DEIMOS stellar radial velocities to see how flat and log-uniform priors affect the inferred dispersions and upper limits. With mock samples of 10 to 1,000 stars and velocity uncertainties from 0.2 to 2 times the true intrinsic dispersion, I compared the bias and reliability of maximum likelihood, restricted maximum likelihood (REML) and Bayesian methods, with particular attention to small samples.
Bayesian model comparison and mock-data tests then show when an intrinsic dispersion can be resolved, and how far an upper limit can be trusted when it cannot.
Small-scale Routly-Spitzer effect in the Milky Way halo
I probed the small-scale variation of neutral and ionized gas in the Milky Way halo, using six blue horizontal-branch stars in two halo regions separated by 20 degrees in Galactic longitude, with 11 quasars as a control sample.
I used VPFIT to fit Voigt profiles to Ca II 3934, 3969 Å and Na I 5891, 5897 Å absorption in high-resolution VLT/UVES spectra, deriving the velocity and column density of each component. I compared the results with the 1952 paper that proposed the Routly-Spitzer effect and with later work that confirmed it on global scales.
I then examined how the Na I/Ca II column-density ratio correlates with the column density of each ion, and how column densities vary with the angular separation between sight lines, and proposed possible physical reasons for the effect we observe.
Earlier projects
Ionizing photon budget in cosmic reionization
A study of the ionizing photon budget crisis proposed in 2024: whether the faint galaxies newly observed by JWST overproduce Lyman-continuum photons, driving reionization earlier than the CMB and Lyα constraints allow. I synthesized the recent literature on faint galaxies, Lyα-emitting galaxies and Lyman-continuum leakers, analyzed the escape fraction, the ionizing photon production efficiency and the clumping factor, and discussed possible resolutions.
Gamma-ray periodicity in active galactic nuclei
I reanalyzed the gamma-ray light curves of five active galactic nuclei with 17 years of Fermi-LAT data, extending 2020 periodicity studies that used nine years. I built a Python search pipeline with six detection methods, including Lomb-Scargle-based approaches, REDFIT, PDM and MCMC sinusoidal fitting, and evaluated the statistical significance of each period. The extended data gave periods consistent with the earlier results for three high-significance sources and confirmed the periodic behavior of two lower-significance candidates.
Gravitational-wave waveform modeling
I compared newly generated gravitational-wave waveforms with existing waveform libraries, using Python to perform waveform matching, as a contribution to the Ripple Python package.