Suprit Singh

Most observational studies of galactic-scale magnetic fields using Faraday rotation rely on estimates of thermal electron densities in galaxies and their radial variations. However, the spatial distribution of electrons in the interstellar medium (ISM) is not clearly known. In this study, we propose and utilize collisionally-excited doublet emission line ratios of [S ii ] λλ 6716, 6731 Å to estimate the electron densities ( n _e ). To map their distribution in the galaxies, we employ IFU spectroscopic observations from the SDSS MaNGA survey, utilising data products from the MaNGA Data Analysis Pipeline (DAP). We present a spatially resolved analysis of 66 face-on galaxies (inclination, i ≤ 15°), including 46 star-forming galaxies (SFGs) and 20 Non-SFGs. Azimuthally averaged radial profiles of n _e are obtained. We found that both SFGs and Non-SFGs exhibit n _e gradients, with higher densities of n _e (S ii ) = 52.87 ± 8.32 cm ^-3 and 99.39 ± 24.37 cm ^-3 , respectively, in the inner disk region (r/R _e ≤ 1.5), which decreases to n _e (S ii ) = 20.92 ± 4.2 cm ^-3 in SFGs and 34.64 ± 11.24 cm ^-3 in Non-SFGs, in the outer disk region (r/R _e > 1.5). We have also analysed these sources with Pipe3D fluxes. We translated n _e to electron column densities ( N _e ) by assuming a typical disk of thickness 1 kpc and note that N _e ∼ 10 ²² cm ^-2 at ∼14 kpc in the disk outer region. We have also discussed the profiles obtained using [O ii ] λλ 3726, 3729 Å doublet. These electron density estimates at different radii provide valuable insights for resolving ambiguities in current and future studies of magnetic fields in galaxies.

Quantum correlations across the horizon could be pivotal in unveiling the puzzles surrounding quantum aspects of black holes and Hawking radiation. The peaks in the equal time correlation function are typically attributed to the entangled particle excitations. In this work, we have investigated the evolution of the correlations of a test quantum field on a dynamical background spacetime undergoing gravitational collapse. In the case of super-critical collapse, as the black hole and its horizon forms, correlated peaks are seen to appear across the horizon, representing an entangled Hawking pair. The outside peak moves away from the horizon as the system evolves, possibly representing outgoing Hawking flux. The implications of these non-local correlations are discussed in light of information paradox, quantum atmosphere and analogue black holes.

Probing magnetic fields in high-redshift galactic systems is crucial to investigate galactic dynamics and evolution. Utilizing the rotation measure of the background quasars, we have developed a radial profile of the magnetic field in a typical high-z galaxy. We have compiled a catalog of 59 confirmed quasar sightlines, having one intervening Mg II absorber in the redshift range 0.372 ≤ z _abs ≤ 0.8. The presence of the foreground galaxy is ensured by comparing the photometric and spectroscopic redshifts within 3σ _z-photo and visual checks. These quasar line-of-sights (LoS) pass through various impact parameters (D) up to 160 kpc, covering the circumgalactic medium of a typical Milky-Way type galaxy. Utilizing the residual rotation measure (RRM) of these sightlines, we estimated the excess in RRM dispersion, σ _ex ^RRM. We found σ _ex ^RRM decreases with increasing D. We translated σ _ex ^RRM to average LoS magnetic field strength, 〈 B _∥ 〉 by considering a typical electron column density. Consequently, the decreasing trend is sustained in the magnetic field. In particular for sightlines with D ≤ 50 kpc and D> 50 kpc, 〈 B _∥ 〉 is found to be 2.39 ± 0.7 μG and 1.67 ± 0.38 μG, respectively. This suggests a clear indication of varying magnetic field from the disk to the circumgalactic medium. This work provides a methodology that, when applied to ongoing and future radio polarisation surveys such as LOFAR and SKA, promises to significantly enhance our understanding of magnetic field mapping in galactic systems.

Motivated by quantum gravity, semi-classical theory, and quantum theory on curved spacetimes, we study the system of an oscillator coupled to two spin-1/2 particles. This model provides a prototype for comparing three types of dynamics: the full quantum theory, the classical oscillator with spin backreaction, and spins propagating on a fixed oscillator background. From nonperturbative calculations of oscillator and entanglement entropy dynamics, we find that entangled tripartite states produce novel oscillator trajectories, and that the three systems give equivalent dynamics for sufficiently weak oscillator-spin couplings, but deviate significantly for intermediate couplings. These results suggest that semiclassical dynamics with back reaction does not provide a suitable intermediate regime between quantum gravity and quantum theory on curved spacetime.

We study a first-order formulation for the coupled evolution of a quantum scalar field and a classical Friedmann universe. The model is defined by a state dependent Hamiltonian constraint and the time dependent Schrödinger equation for the scalar field. We solve the resulting nonlinear equations numerically for initial data consisting of a Gaussian scalar field state and gravity phase space variables. This gives a self-consistent semiclassical evolution that includes nonperturbative “backreaction” due to particle production. We compare the results with the evolution of a quantum scalar field on a fixed background, and find that the backreaction modifies both particle production and cosmological expansion, and that these effects remain bounded.