The formation of clusters and OB associations in different density spiral arm environments

Abstract

We present simulations of the formation and evolution of clusters in spiral arms. The simulations follow two different spiral arm regions, and the total gas mass is varied to produce a range of different mass clusters. We find that including photoionizing feedback produces the observed cluster mass radius relation, increasing the radii of clusters compared to without feedback. Supernovae have little impact on cluster properties. We find that in our high density, high gas mass simulations, star formation is less affected by feedback, as star formation occurs rapidly before feedback has much impact. In our lowest gas density simulation, the resulting clusters are completely different (e.g. the number of clusters and their masses) to the case with no feedback. The star formation rate is also significantly suppressed. The fraction of stars in clusters in this model decreases with time flattening at about 20 per cent. In our lowest gas simulation model, we see the formation of a star forming group with properties similar to an OB association, in particular similar to Orion Ia. We suggest that low densities, and stronger initial dynamics are conducive to forming associations rather than clusters. In all models cluster formation is complex with clusters merging and splitting. The most massive clusters which form have tended to undergo more mergers.

Ionized carbon as a tracer of the assembly of interstellar clouds

“…They can be driven by the complex interplay between gravity and stellar feedback effects, and the thermodynamic response of the multi-phase ISM. In galaxy-wide simulations 45 spiral density waves lead to high-velocity collisions of flows that can form massive OB clusters such as the ones seen in Cygnus X. In any case, our finding will have major ramifications for our understanding of molecular cloud assemblage in the Milky Way and other galaxies.…”

Ionized carbon as a tracer of the assembly of interstellar clouds

“…They can be driven by the complex interplay between gravity and stellar feedback effects, and the thermodynamic response of the multi-phase interstellar medium. In galaxy-wide simulations [45] spiral density waves lead to high-velocity collisions of flows that can form massive OB clusters such as the ones seen in Cygnus X. In any case, our finding will have major ramifications for our understanding of molecular cloud assemblage in the Milky Way and other galaxies.…”

Dust around Massive Stars Is Agnostic to Galactic Environment: New Insights from PHAT/BEAST

“…On the other hand, 3D dust mapping and observations of young stellar objects (YSOs) in the Local Bubble have shown that energy from multiple supernovae can create a shell of molecular gas, fueling subsequent star formation (Zucker et al 2022). At the moment, it is unclear which of these two opposing effects dominates star formation rates on a galactic scale; however, studies using simulations seem to show that the effects of stellar feedback might be dependent on the density of the local ISM around stars (Gatto et al 2015;Dobbs et al 2022).…”

“…While simulations have given us the mechanism to understand how various forms of feedback interact with the ISM on small scales (Peters et al 2011;Dale et al 2014;Chen et al 2015;Geen et al 2015;Choi et al 2017;, it is still difficult to model the effects of feedback across entire galaxies (Girichidis et al 2016;Dobbs et al 2022). Modeling feedback in detail requires subparsec-scale resolution (e.g., TIGRESS; , making it difficult to propagate the effects to the kiloparsec scales of galaxies (e.g., FIRE; Hopkins et al 2014).…”