Katie Kudla and Joaquín Becerra Espinoza

From the calendar

Accurately estimating the Lyman Continuum (LyC) photon escape fraction remains a challenge, as most methods either assume isotropy or are restricted to specific redshift ranges. Upon using integral field spectroscopy to analyze emission line ratios as indirect estimators of LyC escape, we minimize assumptions of isotropy while enabling future comparisons betweengalaxies at low and high redshifts. We construct spatially resolved [OIII]/[OII] flux ratio (O32) maps for eight nearby galaxies with many properties analogous to high-redshift systems. These maps reveal anisotropic O32 ratios, suggesting potential anisotropic LyC escape. We observe negative radial gradients characteristic of ionization-bounded nebulae, along with persistently high ratios that hint at the presence of density-bounded regions. By analyzing these features with photoionization models, we provide preliminary insights into quantitatively distinguishing between these ionization regimes and constraining the LyC escape fraction.

Strong gravitational lensing in galaxy clusters offers a unique method to probe dark matter subhalos by analyzing perturbations to critical curves. This ongoing study focuses on the astrometric shifts in highly magnified, symmetric image pairs of background stars caused by subhalos near the critical curve. In a smooth lensing model, these image pairs align symmetrically with respect to a flat critical curve, but the presence of subhalos induces detectable shifts, disrupting it into a "wiggling" pattern. By comparing observed image positions with theoretical models, we can infer the astrometric shifts and in turn subhalo properties, with early results showing sensitivity to subhalos in the mass range of one to hundreds of millions of solar masses. These astrometric signatures, detectable by instruments like the James Webb Space Telescope, not only provide a powerful tool for constraining dark matter substructure in galaxy clusters, but also a way of distinguishing between Cold Dark Matter (CDM) and alternative models such as Warm Dark Matter (WDM).