arXiv subjects

S. M. R. Jeffreson

Publications and source records attributed to S. M. R. Jeffreson.

3 recordsLinked to original sources

arXiv2026

What Suppresses Star Formation in Bulge-Dominated Early-Type Galaxies?

We investigate the physical origin of star formation suppression in gas-rich early-type galaxies using five high-resolution hydrodynamical idealized galaxy simulations, performed with the moving-mesh code AREPO. These simulations include one Milky Way-like galaxy and four early-type galaxies, of which one early-type galaxy is found to have significantly less star formation despite a substantial molecular gas reservoir. We apply a modified virial theorem to the overdensities in each galaxy to quantify the forces regulating their stability and thus star formation. We find evidence that, in the suppressed galaxy, strong Coriolis forces driven by elevated galactic shear may inhibit gravitational collapse. This is caused by the galaxy's high central compactness, providing a physical mechanism for the suppression of star formation that does not require the removal of molecular gas. In contrast, less compact early-type galaxies host more gravity-dominated clouds and therefore exhibit higher star formation rates. However, we find that this gravitational stability occurs without significantly increasing the classical Toomre-Q parameter, and therefore a new criterion for suppressed star formation may be needed. We also discuss the impact of our choice of overdensity scale and connections to observations of molecular clouds.

astro-ph.GA↗

arXiv2019

The dynamical evolution of molecular clouds near the Galactic Centre - II. Spatial structure and kinematics of simulated clouds

The evolution of molecular clouds in galactic centres is thought to differ from that in galactic discs due to a significant influence of the external gravitational potential. We present a set of numerical simulations of molecular clouds orbiting on the 100-pc stream of the Central Molecular Zone (the central $\sim500$ pc of the Galaxy) and characterise their morphological and kinematic evolution in response to the background potential and eccentric orbital motion. We find that the clouds are shaped by strong shear and torques, by tidal and geometric deformation, and by their passage through the orbital pericentre. Within our simulations, these mechanisms control cloud sizes, aspect ratios, position angles, filamentary structure, column densities, velocity dispersions, line-of-sight velocity gradients, spin angular momenta, and kinematic complexity. By comparing these predictions to observations of clouds on the Galactic Centre 'dust ridge', we find that our simulations naturally reproduce a broad range of key observed morphological and kinematic features, which can be explained in terms of well-understood physical mechanisms. We argue that the accretion of gas clouds onto the central regions of galaxies, where the rotation curve turns over and the tidal field is fully compressive, is accompanied by transformative dynamical changes to the clouds, leading to collapse and star formation. This can generate an evolutionary progression of cloud collapse with a common starting point, which either marks the time of accretion onto the tidally-compressive region or of the most recent pericentre passage. Together, these processes may naturally produce the synchronised starbursts observed in numerous (extra)galactic nuclei.

astro-ph.GA↗

arXiv2018

On the physical mechanisms governing the cloud lifecycle in the Central Molecular Zone of the Milky Way

We apply an analytic theory for environmentally-dependent molecular cloud lifetimes to the Central Molecular Zone of the Milky Way. Within this theory, the cloud lifetime in the Galactic centre is obtained by combining the time-scales for gravitational instability, galactic shear, epicyclic perturbations and cloud-cloud collisions. We find that at galactocentric radii $\sim 45$-$120$ pc, corresponding to the location of the '100-pc stream', cloud evolution is primarily dominated by gravitational collapse, with median cloud lifetimes between 1.4 and 3.9 Myr. At all other galactocentric radii, galactic shear dominates the cloud lifecycle, and we predict that molecular clouds are dispersed on time-scales between 3 and 9 Myr, without a significant degree of star formation. Along the outer edge of the 100-pc stream, between radii of 100 and 120 pc, the time-scales for epicyclic perturbations and gravitational free-fall are similar. This similarity of time-scales lends support to the hypothesis that, depending on the orbital geometry and timing of the orbital phase, cloud collapse and star formation in the 100-pc stream may be triggered by a tidal compression at pericentre. Based on the derived time-scales, this should happen in approximately 20 per cent of all accretion events onto the 100-pc stream.

astro-ph.GA↗