The tidal evolution of dark matter substructure -- I. Subhalo density
  profiles
  Accurately predicting the abundance and structural evolution of dark matter
subhaloes is crucial for understanding galaxy formation, modeling galaxy
clustering, and constraining the nature of dark matter. Due to the nonlinear
nature of subhalo evolution, cosmological $N$-body simulations remain its
primary method of investigation. However, it has recently been demonstrated
that such simulations are still heavily impacted by artificial disruption,
diminishing the information content on small scales and reducing the
reliability of all simulation-calibrated semi-analytical models. In this paper,
we utilize the recently released DASH library of high-resolution, idealized
simulations of the tidal evolution of subhaloes, which are unhindered by
numerical overmerging due to discreteness noise or force softening, to
calibrate an improved, more-accurate model of the evolution of the density
profiles of subhaloes that undergo tidal heating and stripping within their
host halo. By testing previous findings that the structural evolution of a
tidally truncated subhalo depends solely on the fraction of mass stripped,
independent of the details of the stripping, we identify an additional
dependence on the initial subhalo concentration. We provide significantly
improved fitting functions for the subhalo density profiles and structural
parameters ($V_\mathrm{max}$ and $r_\mathrm{max}$) that are unimpeded by
numerical systematics and applicable to a wide range of parameter space. This
model will be an integral component of a future semi-analytical treatment of
substructure evolution, which can be used to predict key quantities, such as
the evolved subhalo mass function and annihilation boost factors, and validate
such calculations performed with cosmological simulations.
