Feedback in Clouds II: UV Photoionisation and the first supernova in a massive cloud

Molecular cloud structure is regulated by stellar feedback in various forms. Two of the most important feedback processes are UV photoionisation and supernovae from massive stars. However, the precise response of the cloud to these processes, and the interaction between them, remains an open question. In particular, we wish to know under which conditions the cloud can be dispersed by feedback, which in turn can give us hints as to how feedback regulates the star formation inside the cloud. We perform a suite of radiative magnetohydrodynamic simulations of a 10^5 solar mass cloud with embedded sources of ionising radiation and supernovae, including multiple supernovae and a hypernova model. A UV source corresponding to 10% of the mass of the cloud is required to disperse the cloud, suggesting that the star formation efficiency should be on the order of 10%. A single supernova is unable to significantly affect the evolution of the cloud. However, energetic hypernovae and multiple supernovae are able to add significant quantities of momentum to the cloud, approximately 10^{43} g cm/s of momentum per 10^{51} ergs of supernova energy. This is on the lower range of estimates in other works, since dense gas clumps that remain embedded inside the HII region cause rapid cooling in the supernova blast. We argue that supernovae alone are unable to regulate star formation in molecular clouds, and that strong pre-supernova feedback is required to allow supernova blastwaves to propagate efficiently into the interstellar mediumComment: 15 pages, 10 figures, submitted to MNRA

On the Indeterministic Nature of Star Formation on the Cloud Scale

Molecular clouds are turbulent structures whose star formation efficiency (SFE) is strongly affected by internal stellar feedback processes. In this paper we determine how sensitive the SFE of molecular clouds is to randomised inputs in the star formation feedback loop, and to what extent relationships between emergent cloud properties and the SFE can be recovered. We introduce the yule suite of 26 radiative magnetohydrodynamic (RMHD) simulations of a 10,000 solar mass cloud similar to those in the solar neighbourhood. We use the same initial global properties in every simulation but vary the initial mass function (IMF) sampling and initial cloud velocity structure. The final SFE lies between 6 and 23 percent when either of these parameters are changed. We use Bayesian mixed-effects models to uncover trends in the SFE. The number of photons emitted early in the cluster's life and the length of the cloud provide are the strongest predictors of the SFE. The HII regions evolve following an analytic model of expansion into a roughly isothermal density field. The more efficient feedback is at evaporating the cloud, the less the star cluster is dispersed. We argue that this is because if the gas is evaporated slowly, the stars are dragged outwards towards surviving gas clumps due to the gravitational attraction between the stars and gas. While star formation and feedback efficiencies are dependent on nonlinear processes, statistical models describing cloud-scale processes can be constructed.Comment: 24 pages, 16 figures, 6 tables. Accepted to MNRAS, version updated with published titl

When H II Regions are Complicated: Considering Perturbations from Winds, Radiation Pressure, and Other Effects

We explore to what extent simple algebraic models can be used to describe H II regions when winds, radiation pressure, gravity and photon breakout are included. We a) develop algebraic models to describe the expansion of photoionised H II regions under the influence of gravity and accretion in power-law density fields with $\rho \propto r^{-w}$, b) determine when terms describing winds, radiation pressure, gravity and photon breakout become significant enough to affect the dynamics of the H II region where $w=2$, and c) solve these expressions for a set of physically-motivated conditions. We find that photoionisation feedback from massive stars is the principal mode of feedback on molecular cloud scales, driving accelerating outflows from molecular clouds in cases where the peaked density structure around young massive stars is considered at radii between $\sim$0.1 and 10-100 pc. Under a large range of conditions the effect of winds and radiation on the dynamics of H II regions is around 10% of the contribution from photoionisation. The effect of winds and radiation pressure are most important at high densities, either close to the star or in very dense clouds such as those in the Central Molecular Zone of the Milky Way. Out to $\sim$0.1 pc they are the principal drivers of the H II region. Lower metallicities make the relative effect of photoionisation even stronger as the ionised gas temperature is higher.Comment: 20 pages, 13 figures, accepted by MNRA

A Detailed Study of Feedback from a Massive Star

We present numerical simulations of a 15 solar mass star in a suite of idealised environments in order to quantify the amount of energy transmitted to the interstellar medium (ISM). We include models of stellar winds, UV photoionisation and the subsequent supernova based on theoretical models and observations of stellar evolution. The system is simulated in 3D using RAMSES-RT, an Adaptive Mesh Refinement Radiation Hydrodynamics code. We find that stellar winds have a negligible impact on the system owing to their relatively low luminosity compared to the other processes. The main impact of photoionisation is to reduce the density of the medium into which the supernova explodes, reducing the rate of radiative cooling of the subsequent supernova. Finally, we present a grid of models quantifying the energy and momentum of the system that can be used to motivate simulations of feedback in the ISM unable to fully resolve the processes discussed in this work.Comment: 19 pages, 12 figures, accepted by MNRA

The energy and dynamics of trapped radiative feedback with stellar winds

In this paper, we explore the significant, non-linear impact that stellar winds have on H ii regions. We perform a parameter study using three-dimensional radiative magnetohydrodynamic simulations of wind and ultraviolet radiation feedback from a 35 M⊙ star formed self-consistently in a turbulent, self-gravitating cloud, similar to the Orion Nebula (M42) and its main ionizing source θ1 Ori C. Stellar winds suppress early radiative feedback by trapping ionizing radiation in the shell around the wind bubble. Rapid breakouts of warm photoionized gas (‘champagne flows’) still occur if the star forms close to the edge of the cloud. The impact of wind bubbles can be enhanced if we detect and remove numerical overcooling caused by shocks crossing grid cells. However, the majority of the energy in the wind bubble is still lost to turbulent mixing between the wind bubble and the gas around it. These results begin to converge if the spatial resolution at the wind bubble interface is increased by refining the grid on pressure gradients. Wind bubbles form a thin chimney close to the star, which then expands outwards as an extended plume once the wind bubble breaks out of the dense core the star formed in, allowing them to expand faster than a spherical wind bubble. We also find wind bubbles mixing completely with the photoionized gas when the H ii region breaks out of the cloud as a champagne flow, a process we term ‘hot champagne’

The SATIN project I: Turbulent multi-phase ISM in Milky Way simulations with SNe feedback from stellar clusters

We introduce the star formation and Supernova (SN) feedback model of the SATIN (Simulating AGNs Through ISM with Non-Equilibrium Effects) project to simulate the evolution of the star forming multi-phase interstellar medium (ISM) of entire disk galaxies. This galaxy-wide implementation of a successful ISM feedback model naturally covers an order of magnitude in gas surface density, shear and radial motions. It is implemented in the adaptive mesh refinement code RAMSES at a peak resolution of 9 pc. New stars are represented by star cluster (sink) particles with individual SN delay times for massive stars. With SN feedback, cooling and gravity, the galactic ISM develops a realistic three-phase structure. The star formation rates naturally follow observed scaling relations for the local Milky Way gas surface density. SNe drive additional turbulence in the warm (300 K < $T$ < 10$^4$ K) gas and increase the kinetic energy of the cold gas, cooling out of the warm phase. The majority of the gas leaving the galactic ISM is warm and hot with mass loading factors of $3 \le \eta \le 10$. While the hot gas is leaving the system, the warm and cold gas falls back onto the disc in a galactic fountain flow.Comment: Submitted to MNRA

Satellite Survival in Highly Resolved Milky Way Class Halos

Surprisingly little is known about the origin and evolution of the Milky Way's satellite galaxy companions. UV photoionisation, supernova feedback and interactions with the larger host halo are all thought to play a role in shaping the population of satellites that we observe today, but there is still no consensus as to which of these effects, if any, dominates. In this paper, we revisit the issue by re-simulating a Milky Way class dark matter (DM) halo with unprecedented resolution. Our set of cosmological hydrodynamic Adaptive Mesh Refinement (AMR) simulations, called the Nut suite, allows us to investigate the effect of supernova feedback and UV photoionisation at high redshift with sub-parsec resolution. We subsequently follow the effect of interactions with the Milky Way-like halo using a lower spatial resolution (50pc) version of the simulation down to z=0. This latter produces a population of simulated satellites that we compare to the observed satellites of the Milky Way and M31. We find that supernova feedback reduces star formation in the least massive satellites but enhances it in the more massive ones. Photoionisation appears to play a very minor role in suppressing star and galaxy formation in all progenitors of satellite halos. By far the largest effect on the satellite population is found to be the mass of the host and whether gas cooling is included in the simulation or not. Indeed, inclusion of gas cooling dramatically reduces the number of satellites captured at high redshift which survive down to z=0.Comment: 22 pages, 16 figures, accepted for publication in MNRA