Forming clusters within clusters: How 30 Doradus recollapsed and gave birth again

TL;DR

This paper explains how a second, younger star cluster in 30 Doradus formed after the first, due to gas re-accretion in a dense molecular cloud, challenging previous feedback-driven models.

Contribution

It demonstrates that gas re-accretion can lead to multiple star formation episodes within a single giant molecular cloud, using the WARPFIELD feedback scheme.

Findings

Re-accretion of gas explains the age offset in NGC 2070.

No need for gas retention or field star capture to explain observations.

Feedback and gravity interplay causes multiple star formation events.

Abstract

The 30 Doradus Nebula in the Large Magellanic Cloud (LMC) contains the massive starburst cluster NGC 2070 with a massive and probably younger stellar sub clump at its center: R136. It is not clear how such a massive inner cluster could form several million years after the older stars in NGC 2070, given that stellar feedback is usually thought to expel gas and inhibit further star formation. Using the recently developed 1D feedback scheme WARPFIELD to scan a large range of cloud and cluster properties, we show that an age offset of several million years between the stellar populations is in fact to be expected given the interplay between feedback and gravity in a giant molecular cloud (GMC) with a density $\gtrsim 500$ cm$^{-3}$ due to re-accretion of gas onto the older stellar population. Neither capture of field stars nor gas retention inside the cluster have to be invoked in order to explain the observed age offset in NGC 2070 as well as the structure of the interstellar medium (ISM) around it.