The Fermi Bubbles

Towering ~25,000 light-years above and below the Galactic center are the Fermi Bubbles — two enormous lobes of hot gas and cosmic rays, first seen in γ-rays, tracing a violent episode of energy injection from the heart of the Milky Way. I probe them using distant quasars and AGN as backlights, measuring ultraviolet absorption from cool gas clouds along the sight line.

• In the first UV-absorption study of the southern bubble (ApJ, 2018) — first author — I mapped the kinematics and chemistry of these high-velocity clouds, showing the nuclear wind is actively entraining cool gas.
• A follow-up in Nature Astronomy (2022) found the clouds span diverse metallicities, pointing to dual origins — some gas lifted out of the disk, some already resident in the halo.

Together these help quantify how activity at the Galactic center recycles gas through the halo — a process central to how galaxies like ours evolve.

Earlier research

Before cosmology, my first projects (as an undergraduate researcher) were in Galactic and stellar astrophysics:

• How far is the Sun above the Galactic plane? A purely geometric measurement of the Sun’s height above the Milky Way’s mid-plane, from the sky positions of stars — Karim & Mamajek (2017), MNRAS.
• How young stars spin up. Measuring the rotation-period distributions of 4–10 Myr T-Tauri stars in Orion OB1 to constrain pre-main-sequence angular-momentum evolution — Karim et al. (2016), AJ, my first first-author paper.