Elizabeth Tarantino (STScI)

The physical processes that govern the interstellar medium and regulate star formation at low metallicity remain poorly understood, yet are critical for interpreting galaxies in the early universe. Observations of nearby metal-poor galaxies that mimic the pristine gas conditions of these distant galaxies are essential to understand the connection between dust, gas, and star formation. In the JWST era, a key tracer of dust is emission from the smallest carbonaceous dust grains, polycyclic aromatic hydrocarbons (PAHs), which dominate mid-infrared spectra of high metallicity galaxies. In metal-poor systems, PAHs are much less abundant relative to the total dust, but the origin of this deficit remains unclear. I will present JWST observations of the 7% Solar metallicity galaxy Sextans A, revealing the lowest metallicity detection of resolved PAH emission to date. The PAH emission is concentrated in compact (3-10 pc) clumps that spatially coincide with tiny CO clouds and host embedded young stellar object (YSO) candidates. Ratios between the 3.3, 7.7, and 11.3 micron PAH features indicate that the PAH grains in Sextans A are small and neutral, with no evidence of significant processing from radiation fields. These findings point to dense, well-shielded regions where PAHs, molecular gas, and stars form together. Collectively, they provide new insight into how dust and stars emerge in galaxies under conditions analogous to those of the early universe.