Periodic Reporting for period 1 - VIA LACTEA (Numerical Simulations of the Milky Way's Accretion History)
Okres sprawozdawczy: 2021-11-01 do 2023-04-30
How did our Galaxy form? What were the major events that shaped the formation and evolution of our Galaxy today? Can we use the present-day positions, motions, chemical compositions and ages of stars in the Milky Way to infer its past? These are some of the big questions driving the study of our Milky Way, commonly known as Galactic Archaeology.
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.
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.
In this first year, we ran idealised hydrodynamical simulations of the interaction of the Gaia-Sausage-Enceladus merger with the Milky Way galaxy to study its dispersial in the stellar halo of the Milky Way as part of a larger programme aimed to study impact of the GSE on the formation and evolution of the MW (GASTRO, led by ERC postdoc Dr. Amarante). Prior experiments have only considered purely N-body experiments, however we show that the various prior passages induce star formation in the GSE progenitor and its dispersial in near integrals of motion space (Energy and Angular momentum) produces complex knots in chemical abundance space which may appear as distinct contributions that could be misinterpreted as debris from smaller satellites. Since the discovery of the GSE debris, many groups are actively searching for clustering of stars in chemodynamical spaces to identify smaller mass objects that may have been accreted in the Milky Way, however based on the interpretation of our models many of these results seem to just point in many instance to misidentification of debris from a common progenitor galaxy.
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.
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 identification of more stream-like structures in the outer disc with Gaia is already a new leap in discovery of Galactic Structure thanks to the Gaia data. These data will be used together with simulations to test new methods to measure the Galactic potential.
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).
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).