Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised
  of Substructure
  In the $\Lambda$CDM paradigm the Galactic stellar halo is predicted to harbor
the accreted debris of smaller systems. To identify these systems, the H3
Spectroscopic Survey, combined with $Gaia$, is gathering 6D phase-space and
chemical information in the distant Galaxy. Here we present a comprehensive
inventory of structure within 50 kpc from the Galactic center using a sample of
5684 giants at $|b|>40^{\circ}$ and $|Z|>2$ kpc. We identify known structures
including the high-$\alpha$ disk, the in-situ halo (disk stars heated to
eccentric orbits), Sagittarius (Sgr), $Gaia$-Sausage-Enceladus (GSE), the Helmi
Streams, Sequoia, and Thamnos. Additionally, we identify the following new
structures: (i) Aleph ([Fe/H]$=-0.5$), a low eccentricity structure that rises
a surprising 10 kpc off the plane, (ii, iii) Arjuna ([Fe/H]$=-1.2$) and I'itoi
([Fe/H]$<-2$), which comprise the high-energy retrograde halo along with
Sequoia, and (iv) Wukong ([Fe/H]$=-1.6$), a prograde phase-space overdensity
chemically distinct from GSE. For each structure we provide [Fe/H],
[$\alpha$/Fe], and orbital parameters. Stars born within the Galaxy are a major
component at $|Z|\sim$2 kpc ($\approx$60$\%$), but their relative fraction
declines sharply to $\lesssim$5$\%$ past 15 kpc. Beyond 15 kpc, $>$80$\%$ of
the halo is built by two massive ($M_{\star}\sim10^{8}-10^{9}M_{\odot}$)
accreted dwarfs: GSE ([Fe/H]$=-1.2$) within 25 kpc, and Sgr ([Fe/H]$=-1.0$)
beyond 25 kpc. This explains the relatively high overall metallicity of the
halo ([Fe/H]$\approx-1.2$). We attribute $\gtrsim$95$\%$ of the sample to one
of the listed structures, pointing to a halo built entirely from accreted
dwarfs and heating of the disk.
