The Tumultuous Lives of Galaxy Halos

Project leader

Funding source

Swedish Research Council - Vetenskapsrådet (VR)

Project Details

Start date: 01/01/2017
End date: 31/12/2022
Funding: 12000000 SEK


Purpose and Aim: All of galaxy formation and evolution – and therefore our understanding of the origin of objects like the Milky Way – is driven by the astrophysics of baryonic material that occurs in the immediate vicinity of galaxies. This ‘circumgalactic medium’ (CGM) is the battleground upon which two competing forces meet: on the one side new gas is accreted from the intergalactic medium, providing the fuel for all star formation; on the other side feedback from the formation of massive stars acts to strip gas and heavy elements from galaxies, and suppress future star formation. This project will produce an energetically complete picture of this multiphase, complex, gaseous CGM, using unique new observational methods that have recently been pioneered by the principle investigator. We will measure the temperature, density, cooling time, and ultimate fate of the circumgalactic gas, targeting phases that were hitherto not possible to image. We will provide vital new constraints for galaxy formation theory, and guide the development of future satellites.

Project Description: With new staff funded by this consolidator grant, we will launch an extensive multi-wavelength campaign to measure the properties of the CGM of star-forming galaxies in various gas phases. These include:

  • the hottest gas (X-ray; temperature near 50 million K) that does the work to launch galaxy outflows and determines the energy budget of superwinds. This involves extensive observational work, based upon the entire public archives of X-ray telescopes;
  • the cooling coronal gas (temperature near 300,000 K), probed here, and for the first time, through OVI emission in the ultraviolet. This is driven by truly unique observations obtained from the Hubble Space Telescope, and provides the complete picture of how rapidly mechanical energy is being drained from galaxy outflows;
  • the cold gas (T < 20,000 K) that is entrained in the wind. This dominates the mass of gas in the CGM, and determines the future of how (and if) star-formation will occur, how heavy elements are removed from galaxies, etc.

This approach of covering all necessary energy and temperature regimes is unique to the project and is driven by large amounts of telescope time that recently have been allocated to the PI of this proposal.

Significance: The theoretical picture of galaxy formation badly needs to be completed with CGM-scale astrophysics. However simulations cannot capture these scales without losing the big picture of galaxy populations, and in the coming decades galaxy formation theory must proceed using empirically-derived astrophysical ‘scaling relations’. Until recently pioneered by the PI of this proposal, some of the techniques required to observe gas in the outer environs of galaxies had not yet been developed. Deploying these observational methods in large samples for the first time – as this project will do – will lead to major advances in our understanding of galaxy formation.

Preliminary results: preliminary results from the Very Large Telescope have revealed the first large-scale (150 kpc) filament of accreting gas, as it falls onto an assembling group of galaxies in the early universe. This is the first time such detections have been made for normal galaxies. Similarly the PI has recently used the HST to detect and image coronal gas (O VI emission) surrounding galaxies, and mapped this phase for the very first time. These observations are the only ones of their kind, as prior to the latest publication it was thought impossible to map this gas with current telescopes. Hence these results will not only guide theory but also the development of future satellite facilities.

Last updated on 2017-30-05 at 12:32