Forensics of subhalo–stream encounters: the three phases of gap growth
Monthly Notices of the Royal Astronomical Society
Oxford University Press
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Erkal, D., & Belokurov, V. (2015). Forensics of subhalo–stream encounters: the three phases of gap growth. Monthly Notices of the Royal Astronomical Society, 450 1136-1149. https://doi.org/10.1093/mnras/stv655
There is hope to discover dark matter subhaloes free of stars (predicted by the current theory of structure formation) by observing gaps they produce in tidal streams. In fact, this is the most promising technique for dark substructure detection and characterization as such gaps grow with time, magnifying small perturbations into clear signatures observable by ongoing and planned Galaxy surveys. To facilitate such future inference, we develop a comprehensive framework for studies of the growth of the stream density perturbations. Starting with simple assumptions and restricting to streams on circular orbits, we derive analytic formulae that describe the evolution of all gap properties (size, density contrast, etc.) at all times. We uncover complex, previously unnoticed behaviour, with the stream initially forming a density enhancement near the subhalo impact point. Shortly after, a gap forms due to the relative change in period induced by the subhalo's passage. There is an intermediate regime where the gap grows linearly in time. At late times, the particles in the stream overtake each other, forming caustics, and the gap grows like √t. In addition to the secular growth, we find that the gap oscillates as it grows due to epicyclic motion. We compare this analytic model to N-body simulations and find an impressive level of agreement. Importantly, when analysing the observation of a single gap we find a large degeneracy between the subhalo mass, the impact geometry and kinematics, the host potential, and the time since flyby.
galaxies: haloes, galaxies: kinematics and dynamics, galaxies: structure, cosmology: theory, dark matter
The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007–2013)/ERC Grant Agreement No. 308024.
External DOI: https://doi.org/10.1093/mnras/stv655
This record's URL: https://www.repository.cam.ac.uk/handle/1810/248977