Photoionizing feedback in spiral arm molecular clouds

This is the author accepted manuscript. The final version is available from Oxford University Press via the DOI in this recordWe present simulations of a 500 pc2 region, containing gas of mass 4 × 106 M⊙, extracted from an entire spiral galaxy simulation, scaled up in resolution, including photoionising feedback from stars of mass > 18 M⊙. Our region is evolved for 10 Myr and shows clustered star formation along the arm generating ≈ 5000 cluster sink particles ≈ 5% of which contain at least one of the ≈ 4000 stars of mass > 18 M⊙. Photoionisation has a noticeable effect on the gas in the region, producing ionised cavities and leading to dense features at the edge of the HII regions. Compared to the no-feedback case, Photoionisation produces a larger total mass of clouds and clumps, with around twice as many such objects, which are individually smaller and more broken up. After this we see a rapid decrease in the total mass in clouds and the number of clouds. Unlike studies of isolated clouds, our simulations follow the long range effects of ionisation, with some already-dense gas, becoming compressed from multiple sides by neighbouring HII regions. This causes star formation that is both accelerated and partially displaced throughout the spiral arm with up to 30% of our cluster sink particle mass forming at distances > 5 pc from sites of sink formation in the absence of feedback. At later times, the star formation rate decreases to below that of the no-feedback case.European Union Horizon 2020European Union FP

Supernovae and photoionizing feedback in spiral arm molecular clouds

This is the author accepted manuscript. The final version is available from Oxford University Press via the DOI in this recordData availability: The data underlying this article will be shared on reasonable request to the corresponding authorWe explore the interplay between supernovae and the ionizing radiation of their progenitors in star forming regions. The relative contributions of these stellar feedback processes are not well understood, particularly on scales greater than a single star forming cloud. We focus predominantly on how they affect the interstellar medium. We re-simulate a 500 pc2 region from previous work that included photoionization and add supernovae. Over the course of 10 Myr more than 500 supernovae occur in the region. The supernovae remnants cool very quickly in the absence of earlier photoionization, but form much larger and more spherical hot bubbles when photoionization is present. Overall, the photoionization has a significantly greater effect on gas morphology and the sites of star formation. However, the two processes are comparable when looking at their effect on velocity dispersion. When combined, the two feedback processes increase the velocity dispersions by more than the sum of their parts, particularly on scales above 5 pc.European Union Horizon 202

Stellar winds and photoionization in a spiral arm

This is the final version. Available from Oxford University Press via the DOI in this recordData availability: The data underlying this paper will be shared on reasonable request to the corresponding author.The role of different stellar feedback mechanisms in giant molecular clouds is not well understood. This is especially true for regions with many interacting clouds as would be found in a galactic spiral arm. In this paper, building on previous work by Bending et al., we extract a 500 pc ×500 pc ×100 pc section of a spiral arm from a galaxy simulation. We use smoothed particle hydrodynamics to re-simulate the region at higher resolution (1 M ⊙per particle). We present a method for momentum-driven stellar winds from main-sequence massive stars, and include this with photoionization, self-gravity, a galactic potential, and interstellar medium heating/cooling. We also include cluster-sink particles with accretion radii of 0.78 pc to track star/cluster formation. The feedback methods are as robust as previous models on individual cloud scales (e.g. Dale et al.). We find that photoionization dominates the disruption of the spiral arm section, with stellar winds only producing small cavities (at most ∼30 pc). Stellar winds do not affect the resulting cloud statistics or the integrated star formation rate/efficiency, unlike ionization, which produces more stars, and more clouds of higher density and higher velocity dispersion compared to the control run without feedback. Winds do affect the sink properties, distributing star formation o v er more low-mass sinks ( ∼10 2 M ⊙) and producing fewer high-mass sinks ( ∼10 3 M ⊙). Overall, stellar winds play at best a secondary role compared to photoionization, and on many measures, they have a negligible impact.European Union Horizon 202

Star cluster formation and feedback in different environments of a Milky Way-like galaxy

This is the author accepted manuscriptData availability: The data underlying this paper will be shared on reasonable request to the corresponding author.It remains unclear how galactic environment affects star formation and stellar cluster properties. This is difficult to address in Milky Way-mass galaxy simulations because of limited resolution and less accurate feedback compared to cloud-scale models. We carry out zoom-in simulations to re-simulate 100–300 pc regions of a Milky Way-like galaxy using smoothed particle hydrodynamics, including finer resolution (0.4 M⊙ per particle), cluster-sink particles, ray-traced photoionization from O stars, H2/CO chemistry, and ISM heating/cooling. We select ∼106 M⊙ cloud complexes from a galactic bar, inner spiral arm, outer arm, and inter-arm region (in order of galactocentric radius), retaining the original galactic potentials. The surface densities of star formation rate and neutral gas follow ΣSFR ∝ Σ 1.3 gas, with the bar lying higher up the relation than the other regions. However, the inter-arm region forms stars 2–3x less efficiently than the arm models at the same Σgas. The bar produces the most massive cluster, the inner arm the second, and the inter-arm the third. Almost all clusters in the bar and inner arm are small (radii < 5 pc), while 30-50 per cent of clusters in the outer arm and inter-arm have larger radii more like associations. Bar and inner arm clusters rotate at least twice as fast, on average, than clusters in the outer arm and inter-arm regions. The degree of spatial clustering also decreases from bar to inter-arm. Our results indicate that young massive clusters, potentially progenitors of globular clusters, may preferentially form near the bar/inner arm compared to outer arm/inter-arm regions.European Commissio

The formation of massive stellar clusters in converging galactic flows with photoionisation

This is the final version. Available from Oxford University Press via the DOI in this recordData availability: The data underlying this paper will be shared on reasonable request to the corresponding author.We have performed simulations of cluster formation along two regions of a spiral arm taken from a global Milky Way simulation, including photoionising feedback. One region is characterised by strongly converging flows, the other represents a more typical spiral arm region. We find that more massive clusters are able to form on shorter timescales for the region with strongly converging flows. Mergers between clusters are frequent in the case of the strongly converging flows and enable the formation of massive clusters. We compare equivalent clusters formed in simulations with and without ionisation. Photoionisation does not prevent massive cluster formation, but can be seen to limit the masses of the clusters. On average the mass is reduced by around 20%, but we see a large spread from ionisation having minimal difference to leading to a 50% reduction in mass. Photoionisation is also able to clear out the gas in the vicinity of the clusters on Myr timescales, which can produce clusters with larger radii that are surrounded by more massive stellar halos. We find that the ionising feedback has more impact in our second region which is less dense and has less strongly converging flows.European Union Horizon 2020Japanese Society for the Promotion of Science (JSPS