arXiv subjects

Kevin Hall

Publications and source records attributed to Kevin Hall.

4 recordsLinked to original sources

arXiv2026

Mapping the Extended Lyman-Alpha Emission within the Circumgalactic Medium of Quasars Hosted by Dusty Starbursts with CubeCarve

We present a study of extended Ly$\alpha$ emission around four quasars hosted by dusty starbursts, which are composite systems thought to represent a transitional stage in quasar evolution. To extract faint CGM emission in the presence of bright point sources, we introduce {\it CubeCarve}, a dual-channel deconvolution algorithm that separates unresolved quasar emission from spatially extended structure. This approach enables reliable recovery of \Lya\ emission projected onto the quasar position without introducing subtraction artifacts. Using {\it CubeCarve}, we find that the \Lya\ surface brightness profiles of these systems are, on average, fainter and shallower than those of quasars of similar bolometric luminosities. We also find that the total integrated \Lya\ luminosities of the nebulae are lower in systems whose host galaxies exhibit brighter far-infrared emission. These results suggest that the CGM conditions in composite systems differ from those in the broader quasar population. Our study highlights both the physical diversity of quasar CGM environments and the effectiveness of {\it CubeCarve} for recovering diffuse emission in modern IFU datasets.

astro-ph.GA↗

arXiv2024

HI Ly$\alpha$ Emission from a Metal-Poor Cool Stream Fueling an Early Dusty Starburst

The GAMA J0913$-$0107 system is a rare conjunction of a submillimeter galaxy (SMG) at $z \approx 2.7$ and two background QSOs with projected separations $<$200 kpc. Previous high-resolution QSO absorption-line spectroscopy has revealed high H $\tiny{\rm I}$ column density, extremely metal-poor ($\sim 1\%$ solar) gas streams in the circumgalactic medium of the SMG. Here we present deep optical integral-field spectroscopy of the system with the Keck Cosmic Web Imager (KCWI). Reaching a $2\sigma$ surface brightness (SB) limit $\approx 10^{-19}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ with $\sim$2 hours of integration time, we detect a filamentary Ly$\alpha$ nebula stretching $\sim$180 kpc from the SMG intercepting both QSO sightlines. This Ly$\alpha$ filament may correspond to the same cool gas stream penetrating through the hot halo seen in the absorption. In contrast to Ly$\alpha$ nebulae around QSOs, there is no obvious local source for photoionization due to the massive dust content. While uncertain, we consider the possibility that the nebula is ionized by shocks induced by the infall, obscured star formation, and/or a boosted UV background. The SMG-QSOs conjunction multiplied the efficiency of the KCWI observations, allowing a direct comparison of Ly$\alpha$ nebulae in two distinct environments. We find that the nebula around the QSOs are much brighter and show steeper surface brightness profiles than the SMG nebula. This is consistent with the additional photoionization and Ly$\alpha$ scattering provided by the QSOs. While illustrating the challenges of detecting Ly$\alpha$ nebulae around SMGs, our work also demonstrates that important insights can be gained from comparative studies of high-$z$ Ly$\alpha$ nebulae.

astro-ph.GA↗

arXiv2000

Restricted feedback control of one-dimensional maps

Dynamical control of biological systems is often restricted by the practical constraint of unidirectional parameter perturbations. We show that such a restriction introduces surprising complexity to the stability of one-dimensional map systems and can actually improve controllability. We present experimental cardiac control results that support these analyses. Finally, we develop new control algorithms that exploit the structure of the restricted-control stability zones to automatically adapt the control feedback parameter and thereby achieve improved robustness to noise and drifting system parameters.

nlin.CD↗

arXiv1997

A theory for the membrane potential of cells

We give an explicit formula for the membrane potential of cells in terms of the intracellular and extracellular ionic concentrations, and derive equations for the ionic currents that flow through channels, exchangers and electrogenic pumps based on simple energy considerations and conservation laws. We demonstrate that the work done by the pump is equal to the potential energy of the cell plus the energy loss due to the downhill ionic fluxes through the channels and the exchanger. Our equations predict osmotic pressure variations. The theory is illustrated in a simple model of spontaneously active cells in the cardiac pacemaker. The simulated action potential and the five currents in the model are in excellent agreement with experiments. The model predicts the experimental observed intracellular ionic concentration of potassium, calcium and sodium. We do not see any drift of the values for the concentrations in a long time simulation, instead we can obtain the same asymptotic values starting with equal intracellular and extracellular ionic concentrations.

physics.bio-ph↗