Periodic Reporting for period 1 - VIA LACTEA (Numerical Simulations of the Milky Way's Accretion History)
Reporting period: 2021-11-01 to 2023-04-30
In the current cosmological model, galaxies form hierarchically through the condensation of baryons into stars at the center of dark matter halos. A galaxy like our Milky Way generally builds up from mergers at high redshifts and later evolves more quiescently to the present-day. However this a number of signs seem to suggest that its evolution may not be as quiescent as previously thought and this may have also important implications for how our Sun was even born, hence understanding the accretion history of our Galaxy and the role of various mergers not only has implications for the dynamics/structure of the Milky Way, but also a chance to study the behaviour of dark matter in ways previously ignored and ultimately figuring out our own origins.
The overall objectives of this project is to gain a better understanding of the role of massive accretion events in shaping the structural properties of the Galaxy from very high-redshift mergers (e.g. Gaia-Sausage-Enceladus or other potentially more ancient merger events) to the present-day subject to known Galactic interactions (the Magellanic Clouds and the Sagittarius dwarf galaxy) and what their repercussions are for the past/current dynamical state of the Milky Way and evolution of galaxies in our own from debris from ancient disrupted galaxies to those presently forming.
We are also preparing genetically modified runs of MW-like galaxies containing GSE-like features (i.e. highly radially anisotropic stellar halos) that identified in a large suite of simulations from the AURIGA project. This necessitated . In parallel we have further analysed the properties of MW-like galaxies containing GSE-like debris.
We have also identified accretion histories reminescent of two massive objects which may be similar to the hypothesised and highly-debated Kraken galaxy. Our results seem to suggest that such a merger would be very difficult to identify chemically because at high redshifts it becomes exceedingly difficult to chemically disentangle the proto-Milky Way to another satellite merger with a ratio of 1:3. However we predict that the effects of double merger could have important impacts on the star formation history of the Galaxy and potentially testable with detailed colour-magnitude diagram fitting method and eventually asteroseismology.
On the more recent accretion events, we have run idealised simulations in preparation for the larger cosmological runs of the LMC and Sgr dwarf galaxy. Particularly given the different masses of MW-like dark matter halos it is necessary to first probe the different plausible orbits for the LMC before embarking on more ambitious runs.
The simulations we have developed not only change the have also been used to test methods of inferring the distribution of dark matter in the plane of the disc that we have helped develop (Widmark et al. 2021, 2022).