arXiv subjects

Rachel Pillsworth

Publications and source records attributed to Rachel Pillsworth.

5 recordsLinked to original sources

arXiv2026

Filamentary Hierarchies and Superbubbles II: Impact of superbubbles and galactic dynamics on filament formation and fragmentation

Large scale phenomena in spiral galaxies such as shear, supernovae, and magnetic fields all contribute to the formation and subsequent evolution of filamentary structure and star formation within them. In this paper, we analyze the properties and dynamics of filaments in a simulated Milky Way-like galaxy from Zhao et al. 2024. Using filament and superbubble structure analysis codes, we investigate the roles of galactic shear, supernovae and superbubbles, and magnetic fields on the stability and fragmentation of filaments. We find that local shear has little effect on filament stability and the largest structures at outer radii of the disk may be more likely to be dissipated by shear than supernovae. Filaments are largely parallel to the magnetic field, which plays a significant role in filament stability. By measuring the ratio of surface pressure on a filament to that on its central spine, $\chi_f=P_{surf}/P_{central}$, we find that filaments with $\chi_f \le 1$ are dominated by their own self gravity and have a strong tendency to be gravitationally supercritical, whereas those with $\chi_f > 1$ are either transitory or in the act of being formed. Finally, we investigate the role of ISM pressure on filament dynamics and stability as a function of galactic radius, finding considerable changes in filament stability and the accompanying star formation rates in the inner versus outer regions of the disk.

astro-ph.GA↗

arXiv2025

Revealing the Connection Between the Filamentary Hierarchy and Star Cluster Formation in a Simulated NGC 628 Galaxy

There is abundant observational evidence for the hierarchical, interconnected nature of filaments in the interstellar medium (ISM) extending from galactic down to sub-parsec scales. New JWST images of NGC 628 in particular, show clusters forming along the two spiral arms of this galaxy. In this paper we investigate filament and cluster properties in an NGC 628-like multi-scale high-resolution magnetohydrodynamic simulation. We use a filament finding tool to identify filaments and derive the probability density functions (PDFs) for the filament lengths and masses. Using a clustering algorithm we identify star clusters formed between 268 to 278 Myr and follow this population as the galaxy evolves for 60 Myr, calculating their mass PDFs, average radius growth rate, and average mass loss rate. We find a power-law index of alpha_m = -1.35 for the filament masses. Calculating the power-law index from our cluster mass PDF, we find a value of alpha_{c,m} = -1.35 when the clusters first form, exactly our filament mass power-law index. This shows that properties of young clusters arise from the gravitational fragmentation of their host filaments. We track the post-formation evolution of the clusters as they become unbound, increase in radius and decrease in mass yielding an ever steeper mass power-law index. After 60 Myr, the mass power-law index is alpha_{c,m} = -1.55, matching other simulations and observations.

astro-ph.GA↗

arXiv2025

Filamentary Hierarchies and Superbubbles I: Characterizing filament properties across a simulated spiral galaxy

High resolution surveys reveal that the interstellar medium in the Milky Way and nearby galaxies consists of interlinked hierarchies of filamentary structure and superbubbles extending from galactic to subpc scales. The characterization of filament properties across this hierarchy is of fundamental importance for the origin of giant molecular clouds and their star clusters. In this paper we characterize the properties of filaments greater than 25 pc in length that are produced in the multi-scale galactic MHD simulations of Zhao et al. 2024. By adapting the FilFinder algorithm of Koch & Rosolowsky, 2015, we extract over 500 filaments ranging up to 10 kpc scales, to derive the probability distribution functions for filament masses and lengths, magnetic field orientations, and the gravitational stability and fragmentation patterns of filaments. We find power-law distributions for filament masses and lengths. The former has a power law index $\alpha_m = 1.85$ that is nearly identical to that of observed GMC mass functions in extragalactic and Galactic surveys, suggesting that GMC properties are inherited from their host filaments. The fragmentation of magnetized filaments on 200 pc scales or less occurs when they exceed an average critical line mass, as predicted by theory. On larger scales however, kpc filaments form out of the cold neutral medium (CNM) and fragmentation follows local variations in the critical line mass along spiral arms or at the boundaries of superbubbles.

astro-ph.GA↗

arXiv2024

Filamentary Hierarchies and Superbubbles: Galactic Multiscale MHD Simulations of GMC to Star Cluster Formation

There is now abundant observational evidence that star formation is a highly dynamical process that connects filament hierarchies and supernova feedback from galaxy scale kpc filaments and superbubbles, to giant molecular clouds (GMCs) on 100 pc scales and star clusters (1 pc). Here we present galactic multi-scale MHD simulations that track the formation of structure from galactic down to sub pc scales in a magnetized, Milky Way like galaxy undergoing supernova driven feedback processes. We do this by adopting a novel zoom-in technique that follows the evolution of typical 3-kpc sub regions without cutting out the surrounding galactic environment, allowing us to reach 0.28 pc resolution in the individual zoom-in regions. We find a wide range of morphologies and hierarchical structure including superbubbles, turbulence, kpc atomic gas filaments hosting multiple GMC condensations that are often associated with superbubble compression; down to smaller scale filamentary GMCs and star cluster regions within them. Gas accretion and compression ultimately drive filaments over a critical, scale - dependent, line mass leading to gravitational instabilities that produce GMCs and clusters. In quieter regions, galactic shear can produce filamentary GMCs within flattened, rotating disk-like structures on 100 pc scales. Strikingly, our simulations demonstrate the formation of helical magnetic fields associated with the formation of these disk like structures.

astro-ph.GA↗

arXiv2024

Necessary conditions for the formation of filaments and star clusters in the cold neutral medium

Star formation takes place in filamentary molecular clouds which arise by physical processes that take place in the cold, neutral medium (CNM). We address the necessary conditions for this diffuse ($n \approx 30$ cm$^{-3}$), cold (T $\approx$ 60 K), magnetized gas undergoing shock waves and supersonic turbulence, to produce filamentary structures capable of fragmenting into cluster forming regions. Using RAMSES and a magnetized CNM environment as our initial conditions, we simulate a 0.5 kpc turbulent box to model a uniform gas with magnetic field strength of 7 $μG$, varying the 3D velocity dispersion via decaying turbulence. We use a surface density of $320 M_{\odot} pc^{-2}$, representative of the inner 4.0 kpc CMZ of the Milky Way and typical luminous galaxies. Filamentary molecular clouds are formed dynamically via shocks within a narrow range of velocity dispersions in the CNM of 5 - 10 km/s with a preferred value at 8 km/s. Cluster sink particles appear in filaments which exceed their critical line mass, occurring optimally for velocity dispersions of 8 km/s. Tracking the evolution of magnetic fields, we find that they lead to double the dense star forming gas than in purely hydro runs. Perpendicular orientations between magnetic field and filaments can increase the accretion rates onto filaments and hence their line masses. Because magnetic fields help support gas, MHD runs result in average temperatures an order of magnitude higher than unmagnetized counterparts. Finally, we find magnetic fields delay the onset of cluster formation by $\propto 0.4$ Myr.

astro-ph.GA↗