Tidal Stripping in the Adiabatic Limit

Abstract

We present a model for the remnants of haloes that have gone through an adiabatic tidal stripping process. We show that this model exactly reproduces the remnant of an NFW halo that is exposed to a slowly increasing isotropic tidal field and approximately for an anisotropic tidal field. The model can be used to predict the asymptotic mass loss limit for orbiting subhaloes, solely as a function of the initial structure of the subhalo and the value of the tidal field at pericentre. Predictions can easily be made for differently concentrated host-haloes with and without baryonic components, which differ most notably in their relation between pericentre radius and tidal field. The model correctly predicts several empirically measured relations such as the 'tidal track' and the 'orbital frequency relation' that was reported by Errani & Navarro (2021) for the case of an isothermal sphere. Further, we discover the 'structure-tide' degeneracy which implies that increasing the concentration of a subhalo has exactly the same impact on tidal stripping as reducing the amplitude of the tidal field. Beyond this, we find that simple relations hold for the bound mass, truncation radius, WIMP annihilation luminosity and tidal ratio of tidally stripped NFW haloes in relation to quantities measured at the radius of maximum circular velocity. Finally, we note that NFW haloes cannot be completely disrupted when exposed adiabatically to tidal fields of arbitrary magnitudes. We provide an open-source implementation of our model and suggest that it can be used to improve predictions of dark matter annihilation.

Shedding light on low-mass subhalo survival and annihilation luminosity with numerical simulations

“…First of all, we want to understand if also in the case of including baryons the results are scale-free when the subhalo mass is small enough. This was only shown before for the DM-only case (Ogiya et al 2019, see also Stücker et al 2022). Our findings are depicted in the left panel of Fig.…”

“…First, in Section 4.1, we show that most dependence of the mass loss on orbital parameters can be summarized through its dependence on the pericentre radius of the orbit. As a further simplification, we show in Section 4.2 that baryonic and DM-only cases follow the same relation when the pericentre tidal field is considered as the primary parameter instead and further, that also the concentration dependence can be explained by defining a single effective tidal field parameter that takes into account the structure-tide degeneracy (Stücker et al 2022).…”

“…The results of our study are depicted in Section 3, giving special attention to two quantities, the bound mass fraction and the annihilation luminosity, both for runs without and with baryons. In Section 4, we discuss our main findings and compare them to the results in the companion paper, Stücker et al (2022), where we present an analytical model that treats tidal stripping in the adiabatic limit to predict lower bounds on the asymptotic remnants of subhaloes. Finally, we conclude in Section 5.…”

“…Bullock et al 2000;Okamoto et al 2008). While we employ the subhalo mass of 𝑚 sub = 10 6 M in our main simulations, the simulation results can be, in principle, scaled down to arbitrarily small halo masses (Stücker et al 2022). Specifically, in this work we have tested subhalo masses down to 1 M (see Section 3.1.2).…”

“…Indeed, it is unclear whether small subhaloes will survive the strong tidal forces within their hosts since their accretion times to present (Hayashi et al 2003;van den Bosch et al 2018;van den Bosch & Ogiya 2018). Some authors claim that almost all subhalo disruption is of numerical origin and a bound remnant should always survive (van den Bosch et al 2018;Ogiya et al 2019;Errani & Peñarrubia 2020;Green et al 2021;Amorisco 2021;Stücker et al 2022), while other studies suggest that the abundance of small subhaloes is severely reduced due to the effect of tidal forces and of other dynamical agents such as the presence of baryonic material (Garrison-Kimmel et al 2017;Kelley et al 2019;Grand & White 2021;Grand et al 2021). There is about five times more DM than baryonic matter, hence the first one often governs the dynamics.…”