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We present evidence for very high gas fractions and extended molecular gasreservoirs in normal, near-infrared selected (BzK) galaxies at z~1.5, based onmulti-configuration CO[2-1] observations obtained at the IRAM PdBI. Six of thesix galaxies observed were securely detected. High resolution observationsresolve the CO emission in four of them, implying sizes of order of 6-11 kpcand suggesting the presence of rotation. The UV morphologies are consistentwith clumpy, unstable disks, and the UV sizes are consistent with the CO sizes.The star formation efficiencies are homogeneously low and similar to localspirals - the resulting gas depletion times are ~0.5 Gyr, much higher than whatis seen in high-z submm galaxies and quasars. The CO luminosities can bepredicted to within 0.15 dex from the star formation rates and stellar masses,implying a tight correlation of the gas mass with these quantities. We usedynamical models of clumpy disk galaxies to derive dynamical masses. Thesemodels are able to reproduce the peculiar spectral line shapes of the COemission. After accounting for the stellar and dark matter masses we derive gasmasses of 0.4-1.2x10^11 Msun. The conversion factor is very high:alpha_CO=3.6+-0.8, consistent with the Galaxy but four times higher than thatof local ultra-luminous IR galaxies. The gas accounts for an impressive 50-65%of the baryons within the galaxies' half light radii. We are witnessing trulygas-dominated galaxies at z~1.5, a finding that explains the high specific SFRsobserved for z>1 galaxies. The BzK galaxies can be viewed as scaled-up versionsof local disk galaxies, with low efficiency star formation taking place insideextended, low excitation gas disks. They are markedly different than localULIRGs and high-z submm galaxies, which have more excited and compact gas.

Very High Gas Fractions and Extended Gas Reservoirs in z=1.5 Disk Galaxies