Maria F. Perez Mendoza

arXiv2026

Improved dark matter measurements with flexible modeling of resolved strongly-lensed quasar narrow-line emission

The relative brightnesses of strongly lensed quasar images, called flux ratios, respond to perturbations from low-mass dark matter halos, enabling tests of dark matter models. The quasar narrow-line region (NLR) is ideal for flux-ratio studies: large enough to be insensitive to stellar microlensing, yet compact enough to remain sensitive to dark matter halo substructure. While nuclear emission dominates NLR flux, many quasars show low surface brightness extended emission spanning kiloparsec scales that could bias measurements. To test this potential bias, we generated mock Keck OSIRIS AO observations of seven $z<1$, $L_\mathrm{bol}\sim10^{46}$ erg s$^{-1}$ quasars characteristic of sources. Only one system shows detectable extended emission after lensing. We introduce a new pipeline for simultaneously fitting point sources (nuclear) + Sérsic elliptical profiles (extended [O\,III]). We show that we recover the true flux-ratios to $<5\%$ even when the extended emission is boosted to 100 times its original flux. We also demonstrate that visual inspection of lenses reliably determines whether to use point-source-only or include extended emission modeling in the pipeline; both achieve $<5\%$ accuracy -- which is below the typical spectral fitting precision. The new pipeline and fitting procedure ensures reliable flux-ratio measurements can be made of narrow-line flux ratios for the thousands of lenses which will be discovered by Euclid, Rubin and Roman Space Telescopes.

astro-ph.CO↗

arXiv2021

Critical phenomena in the gravitational collapse of electromagnetic dipole and quadrupole waves

We report on critical phenomena in the gravitational collapse of electromagnetic waves. Generalizing earlier results that focused on dipole electromagnetic waves, we here compare with quadrupole waves in axisymmetry. We perform numerical simulations of dipole and quadrupole wave initial data, fine-tuning both sets of data to the onset of black hole formation in order to study the critical solution and related critical phenomena. We observe that different multipole moments have different symmetries, indicating that the critical solution for electromagnetic waves cannot be unique, at least not globally. This is confirmed in our numerical simulations: while dipole data lead to a single center of collapse, at the center of symmetry, quadrupole data feature two separate centers of collapse on the symmetry axis, above and below the center of symmetry -- reminiscent of similar findings reported for critical collapse of vacuum gravitational waves. While the critical solution for neither the dipole nor the quadrupole data is exactly self-similar, we find that their approximate echoing periods appear to differ, as do the critical exponents. We discuss whether the centers of collapse found for dipole and quadrupole data might all have the same properties, which would suggest a "local uniqueness" of the critical solution. Instead, we provide some evidence -- including the differing echoing periods and critical exponents -- suggesting that the critical solutions are distinct even locally. We speculate on the implications of our findings for critical phenomena in the collapse of vacuum gravitational waves, which share with electromagnetic waves the absence of a spherically symmetric critical solution.

gr-qc↗