Unveiling the first black holes with JWST: multi-wavelength spectral
  predictions
  Growing the supermassive black holes (~10^9 Msun) that power the detected
luminous, highest redshift quasars (z > 6) from light seeds - the remnants of
the first stars - within ~ 1 Gyr of the Big Bang poses a timing challenge for
growth models. The formation of massive black hole seeds via direct collapse
with initial masses ~ 10^4 - 10^5 Msun alleviates this problem. Physical
conditions required to form these massive direct collapse black hole (DCBH)
seeds are available in the early universe. These viable DCBH formation sites,
satellite halos of star-forming galaxies, merge and acquire a stellar
component. These produce a new, transient class of objects at high redshift,
Obese Black hole Galaxies (OBGs), where the luminosity produced by accretion
onto the black hole outshines the stellar component. Therefore, the OBG stage
offers a unique way to discriminate between light and massive initial seeds. We
predict the multi-wavelength energy output of OBGs and growing Pop III remnants
at a fiducial redshift (z = 9), exploring both standard and slim disk accretion
onto the growing central black hole for high and low metallicities of the
associated stellar population. With our computed templates, we derive the
selection criteria for OBGs, that comprise a pre-selection that eliminates blue
sources; followed by color-color cuts ([F_{070W} - F_{220W}] > 0; -0.3 <
[F_{200W} - F_{444W}] < 0.3) and when available, a high ratio of X-ray flux to
rest-frame optical flux (F_X/F_{444W} >> 1) (Abridged).
