Star formation and galaxy evolution in the nearby, resolved Universe

Throughout their entire lives, massive stars - i.e. stars with masses greater than 8 times that of the Sun - have a deep impact on their surroundings, not only on the small (tens of light years) scales of the regions they form in, but also on the large (hundreds to thousands of light years) scales of their host galaxies. At the beginning of their lives, while still forming, massive, young stars produce energetic bipolar jets which propagate into, and interact with, the surrounding interstellar matter. During their lives, they produce strong stellar winds and ionizing radiation which clear bubble-shaped regions of glowing, ionized gas around them. Ultimately, they will end their lives as powerful supernova explosions that stir up enormous amounts of matter on galactic scales. These so-called feedback mechanisms are responsible for producing the heavy elements (and hence life) in the Universe, disrupting and destroying star-forming clouds of interstellar matter, driving the formation of new generations of stars, and even regulating the matter-cycle of entire galaxies.

The star-forming complex N180 in the Large Magellanic Cloud is filled with massive O-type stars. Their strong radiation and stellar winds ionise and clear the gas around them, shaping the gas and affecting the formation of new stellar generations. This image was taken with the MUSE instrument on the VLT, and traces the ionized gas around the massive stars (red is [SII], green is H_alpha, and blue is [OIII]). With these data, we quantified stellar feedback in the star-forming regions in this complex (McLeod et al., 2019). Image credit: ESO, A. McLeod.

Yet, despite a qualitative theoretical understanding of these feedback mechanisms, our quantitative knowledge of feedback from massive stars is severely lacking. This leads to stellar feedback and its role in regulating how galaxies convert gas into stars to be among the most unconstrained problems in modern astrophysics. Indeed, state-of-the-art numerical simulations of star-forming molecular clouds and galaxy evolution cannot reproduce key observables (e.g., the star formation rate vs. stellar mass relation) without accounting for stellar feedback.

To make progress in the field, understand how feedback changes across the Universe, and provide the simulations with the necessary empirical calibrations, our research aims at delivering a statistically representative number of feedback observations in the nearby Universe, systematically quantifying the various feedback effects throughout the lifetime of massive stars. We use data from so-called integral field units (IFUs) like MUSE on the Very Large Telescope (VLT): these instruments are by far superior to conventional imaging or spectroscopy in this field, as they allow to simultaneously obtain large-scale observations of the feedback-affected interstellar matter and identify and classify the feedback-driving massive stars. IFUs become truly powerful in quantifying stellar feedback when combined with high spatial resolution imaging, e.g. from the Hubble Space Telescope (HST). This allows us to resolve individual massive stars across entire nearby galaxies, and therefore explore stellar feedback in a variety of different environments (McLeod et al. 2020). To fully capture stella feedback throughout the lifecycle of molecular clouds, we can then combine the optical IFU data with multi-wavelength observations ranging from the X-rays to the millimeter regimes.

Staff involved in this project at Durham include Anna McLeod.