The formation and the orbital evolution of main-sequence (MS) binaries are not well understood. The challenge is that the age of binaries is very difficult to measure, and therefore there is no strong constraint on the formation timescales for short-period (<1 day) MS binaries. In Hwang & Zakamska (accepted), we use kinematics as a proxy for stellar age, and show that short-period MS binaries formed with a delay of ~1 Gyr. This delayed formation time supports that these short-period MS binaries are formed via the three-body interaction and/or magnetic winds.
Our VODKA (Varstrometry for Off-nucleus and Dual sub-Kpc AGN) team is currently developing a new way to detect sub-kpc dual AGN and off-nucleus AGN using varstrometry. Varstrometry is a combination of variability and astrometry: with high-precision astrometry, we aim to detect the astrometric jitter caused by the unresolved, variable double-core (or offset) sources. Our exploration of varstrometry in Gaia DR2 is present in Hwang et al. (2020), and its implication for off-nucleus AGN is present in Shen et al. (2019). Many follow-ups for VODKA are coming soon!
Galaxies grow in mass and size over cosmic time, both as a result of mergers, and via accretion of gas from the circumgalactic medium. As the inflow dilutes the metals in the gas, the metallicity distribution becomes a powerful way to search for gas accretion. Advised by Tim Heckman, Jorge Barrera-Ballesteros and Kate Rowlands, Hwang et al. (2019) search for these low-metallicity regions in nearby galaxies. These regions (blue and purple spaxels in the panels) are present in both interacting and non-interacting galaxies. These low-metallicity regions may be signposts to galaxies caught in the act of growing via accretion.
The origin of radio emission in radio-quiet quasars is still not well understood. In the scenario of quasar wind, the synchrotron emission in radio is a by-product of radiatively driven winds. Advised by Nadia L. Zakamska, Hwang et al. (2018) investigated this by studying the population of extremely red quasars, who are among the most powerful quasars in the Universe. They (orange and red symbols in the figure) closely follow the correlation between [OIII] velocity width (wind indicator) and radio luminosity, strongly supporting that wind as a contributor to radio emission in radio-quiet quasars.
I'm also involved in the study of magnetic fields in stellar jets and protostellar system. Our team worked on the Goldreich-Kylafis Effect to infer the magnetic field morphology from the obserfved molecular polarization (Lee+14). With ALMA observation, we also studied the kinematics of the rotational disk in a protostellar system, which may support the scenario that magnetic fields brake the infalling gas and therefore shape the Keperian disk. Lee+16).