Detections of CO Molecular Gas in 24um-Bright ULIRGs at z~2 in the
  Spitzer First Look Survey
  We present CO observations of 9 ULIRGs at z~2 with S(24\mu m)>1mJy,
previously confirmed with the mid-IR spectra in the Spitzer First Look Survey.
All targets are required to have accurate redshifts from Keck/GEMINI near-IR
spectra. Using the Plateau de Bure millimeter-wave Interferometer (PdBI) at
IRAM, we detect CO J(3-2) [7 objects] or J(2-1) [1 object] line emission from 8
sources with integrated intensities Ic ~(5-9)sigma. The CO detected sources
have a variety of mid-IR spectra, including strong PAH, deep silicate
absorption and power-law continuum, implying that these molecular gas rich
objects at z~2 could be either starbursts or dust obscured AGNs. The measured
line luminosity L'[CO] is (1.28-3.77)e+10[K km/s pc^2]. The averaged molecular
gas mass M(H2) is 1.7e+10Msun, assuming CO-to-H2 conversion factor of
0.8Msun/[K km/s pc^2]. Three sources (33%) -- MIPS506, MIPS16144 & MIPS8342 --
have double peak velocity profiles. The CO double peaks in MIPS506 and
MIPS16144 show spatial separations of 45kpc and 10.9kpc, allowing the estimates
of the dynamical masses of 3.2e+11*sin^(-2)(i)Msun and 5.4e+11*sin^{-2}(i)Msun
respectively. The implied gas fraction, M(gas)/M(dyn), is 3% and 4%, assuming
an average inclination angle. Finally, the analysis of the HST/NIC2 images,
mid-IR spectra and IR SED revealed that most of our sources are mergers,
containing dust obscured AGNs dominating the luminosities at (3-6)um. Together,
these results provide some evidence suggesting SMGs, bright 24um z~2 ULIRGs and
QSOs could represent three different stages of a single evolutionary sequence,
however, a complete physical model would require much more data, especially
high spatial resolution spectroscopy.
