Tidal stripping of dark matter subhalos by baryons from analytical perspectives: disk shocking and encounters with stars
Résumé
The cold dark matter (CDM) scenario predicts that galactic halos should host a huge amount of subhalos possibly as light as or lighter than planets, depending on the nature of dark matter. Predicting their abundance and distribution on such small scales has important implications for dark matter searches and searches for subhalos themselves, which could provide a decisive test of the CDM paradigm. A major difficulty in subhalo population model building is to account for the gravitational stripping induced by baryons, which strongly impact on the overall dynamics within the scale radii of galaxies. In this paper, we focus on these ``baryonic'' tides from analytical perspectives, summarizing previous work on galactic disk shocking, and thoroughly revisiting the impact of individual encounters with stars. For the latter, we go beyond the reference calculation of Gerhard and Fall (1983) to deal with penetrative encounters, and provide new analytical results. Based upon a full statistical analysis of subhalo energy change during multiple stellar encounters possibly occurring during disk crossing, we show how subhalos lighter than $\sim 1$~\msun\ are very efficiently pruned by stellar encounters, and how that modifies their mass function in a stellar environment. If reasonably resilient, surviving subhalos have lost all their mass but the inner cusp, with a tidal mass function strongly departing from the cosmological one; otherwise, their number density can drop by an order of magnitude at the solar position in the Milky Way with respect to disk-shocking effects only. For illustration, we integrate these results into our analytical subhalo population model. They can easily be incorporated to any other analytical or numerical approach. This study complements those using cosmological simulations, which cannot resolve dark matter subhalos on such small scales.
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