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\subsection{Simulations}  Words. To infer the virial-infall times of satellite dwarf galaxies in a fully hierarchical cosmological context, we use ELVIS (Exploring the Local Volume in Simulations), a suite of cosmological zoom-in $N$-body simulations that are targeted to modeling the LG \citep{GarrisonKimmel2014}.  ELVIS was run using \textsc{GADGET-3} and \textsc{GADGET-2} \citep{Springel2005e}, with initial conditions generated using \textsc{MUSIC} \citep{HahnAbel2011}, all with $\Lambda$CDM cosmology based on WMAP7 \citep{Larson2011}: $\sigma_8 = 0.801$, $\omegamatter = 0.266$, $\omegalambda = 0.734$, $n_s = 0.963$ and $h = 0.71$.  Within the zoom-in regions, the particle mass is $1.9 \times 10 ^ 5 M_\odot$ and the Plummer-equivalent force softening is $140 \pc$ (comoving at $z > 9$, physical at $z < 9$).  ELVIS contains 48 dark-matter halos of masses similar to the MW or M31 ($\mvir = 1.0 - 2.8 \times 10 ^ {12} \msun$).  Half of these halos are located in zoom-in regions that were selected to contain a pair of halos that resemble the masses, distance, and relative velocity of the MW-M31 pair, while the other half are single isolated halos matched in masses to the paired ones.  Here, we use all halos, finding no significant differences in satellite infall times in using just paired or isolated halos, in agreement with \citet{Wetzel2015}.  ELVIS identifies dark-matter (sub)halos using the six-dimensional halo finder \textsc{rockstar} \citep{Behroozi2013a} and constructs merger trees using the \textsc{consistent-trees} algorithm \citep{Behroozi2013b}.  For each halo that is not a subhalo (see below), we assign a virial mass, $\mvir$, and radius, $\rvir$, using the evolution of the virial relation from \citet{BryanNorman1998} for our $\Lambda$CDM cosmology.  We define a ``subhalo'' as a halo whose center is inside $\rvir$ of a host halo.  When a (sub)halo passes within $\rvir$ of a host halo, the (sub)halo becomes its ``satellite'' and experiences ``virial infall''.  For each (sub)halo, we compute the peak mass, $\mpeak$, that it reached along the history of its primary progenitor.  To assign stellar mass, we use the relation from abundance matching to ELVIS subhalos in \citet{GarrisonKimmel2014}, which reproduces the observed mass function at $\mstar < 10 ^ 9 \msun$ in the LG if one accounts for observational incompleteness \citep{Tollerud2008, Hargis2014}.  Admittedly, the relation between stellar mass and subhalo mass for dwarf galaxies is highly uncertain, likely with significant scatter.  However, as \citet{Wetzel2015} showed...  See \citet{GarrisonKimmel2014} for more details on ELVIS, and \citet{Wetzel2015} for more details on computing satellite infall times.