KMOS^3D: Dynamical constraints on the mass budget in early star-forming
  disks
  We exploit deep integral-field spectroscopic observations with KMOS/VLT of
240 star-forming disks at 0.6 < z < 2.6 to dynamically constrain their mass
budget. Our sample consists of massive ($\gtrsim 10^{9.8} M_\odot$) galaxies
with sizes $R_e \gtrsim 2$ kpc. By contrasting the observed velocity and
dispersion profiles to dynamical models, we find that on average the stellar
content contributes $32^{+8}_{-7}\%$ of the total dynamical mass, with a
significant spread among galaxies (68th percentile range f_star ~ 18 - 62%).
Including molecular gas as inferred from CO- and dust-based scaling relations,
the estimated baryonic mass adds up to $56^{+17}_{-12}\%$ of total for the
typical galaxy in our sample, reaching ~ 90% at z > 2. We conclude that baryons
make up most of the mass within the disk regions of high-redshift star-forming
disk galaxies, with typical disks at z > 2 being strongly baryon-dominated
within $R_e$. Substantial object-to-object variations in both stellar and
baryonic mass fractions are observed among the galaxies in our sample, larger
than what can be accounted for by the formal uncertainties in their respective
measurements. In both cases, the mass fractions correlate most strongly with
measures of surface density. High $\Sigma_{star}$ galaxies feature stellar mass
fractions closer to unity, and systems with high inferred gas or baryonic
surface densities leave less room for additional mass components other than
stars and molecular gas. Our findings can be interpreted as more extended disks
probing further (and more compact disks probing less far) into the dark matter
halos that host them.
