The Interstellar Medium Properties of Heavily Reddened Quasars &
  Companions at z~2.5 with ALMA & JVLA
  We study the interstellar medium (ISM) properties of three heavily reddened
quasars at $z\sim2.5$ as well as three millimetre-bright companion galaxies
near these quasars. New JVLA and ALMA observations constrain the CO(1-0),
CO(7-6) and [CI]$^3$P$_2-^3$P$_1$ line emission as well as the far infrared to
radio continuum. The gas excitation and physical properties of the ISM are
constrained by comparing our observations to photo-dissociation region (PDR)
models. The ISM in our high-redshift quasars is composed of very high-density,
high-temperature gas which is already highly enriched in elements like carbon.
One of our quasar hosts is shown to be a close-separation ($<$2 arcsec) major
merger with different line emission properties in the millimeter-bright galaxy
and quasar components. Low angular resolution observations of high-redshift
quasars used to assess quasar excitation properties should therefore be
interpreted with caution as they could potentially be averaging over multiple
components with different ISM conditions. Our quasars and their companion
galaxies show a range of CO excitation properties spanning the full extent from
starburst-like to quasar-like spectral line energy distributions. We compare
gas masses based on CO, CI and dust emission, and find that these can disagree
when standard assumptions are made regarding the values of $\alpha_{\rm{CO}}$,
the gas-to-dust ratio and the atomic carbon abundances. We conclude that the
ISM properties of our quasars and their companion galaxies are diverse and
likely vary spatially across the full extent of these complex, merging systems.
