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On the origin and morphology of the accreted globular cluster streams and their “cocoons”, and constraints on the dark matter sub-halos

Khyati Malhan (Dept.of Physics, Stockholm University)

Tidally disrupted globular cluster streams are usually perceived as narrow one-dimensional structures in the 6D phase-space. Precisely for this reason, stellar streams have recently gained a lot of popularity in the field of astrophysics, since the orbits of these structures can then be modelled to probe the gravitational potential and the dark matter distribution of the Milky Way galaxy.
Recently, in we showed that the GD-1 stream ( 30 pc wide), which is the tidal debris of a disrupted globular cluster, possesses a secondary diffuse and extended stellar component (∼100 pc wide) around it. Much like a “cocoon”. This we do using the data from Gaia DR2, SEGUE and LAMOST. Similar morphological properties are seen in synthetic streams (from cosmological simulations) that are produced from star clusters that are formed within dark matter sub-halos and then accrete onto a massive host galaxy. This lends credence to the idea that the globular cluster progenitor of the GD-1 stream was originally formed outside of the Milky Way in a now defunct dark satellite galaxy.

The talk aims at highlighting these newly found results, their implications in the studies of galaxy formation, and the importance they may hold in probing dark matter.