We present ~0.6" resolution IRAM PdBI interferometry of eight submillimeter galaxies at z~2 to 3.4, where we detect continuum at 1mm and/or CO lines at 3 and 1 mm. The CO 3-2/4-3 line profiles in five of the sources are double-peaked, indicative of orbital motion either in a single rotating disk or of a merger of two galaxies. The millimeter line and continuum emission is compact; we marginally resolve the sources or obtain tight upper limits to their intrinsic sizes in all cases. The median FWHM diameter for these sources and the previously resolved sources, SMMJ023952-0136 and SMMJ140104+0252 is ≤0.5" (4 kpc). The compactness of the sources does not support a scenario where the far-IR/submm emission comes from 1 Based on observations obtained at the IRAM Plateau de Bure Interferometer (PdBI). IRAM is funded by the Centre National de la Recherche Scientifique (France), the Max-Planck Gesellschaft (Germany), and the Instituto Geografico Nacional (Spain). a cold (T<30 K), very extended dust distribution. These measurements clearly show that the submillimeter galaxies we have observed resemble scaled-up and more gas rich versions of the local Universe, ultra-luminous galaxy (ULIRG) population. Their central densities and potential well depths are much greater than in other z~2-3 galaxy samples studied so far. They are comparable to those of elliptical galaxies or massive bulges. The SMG properties fulfill the criteria of 'maximal' starbursts, in which most of the available initial gas reservoir of 10 10 -10 11 M is converted to stars on a time scale ~3-10 t dyn~a few 10 7 years.

In this paper, we present results from an Institut de Radio Astronomie Millimétrique (IRAM) Plateau de Bure millimetre‐wave Interferometer (PdBI) survey for carbon monoxide (CO) emission towards radio‐detected submillimetre galaxies (SMGs) with known optical and near‐infrared spectroscopic redshifts. Five sources in the redshift range z∼ 1–3.5 were detected, nearly doubling the number of SMGs detected in CO. We summarize the properties of all 12 CO‐detected SMGs, as well as six sources not detected in CO by our survey, and use this sample to explore the bulk physical properties of the submillimetre galaxy (SMG) population as a whole. The median CO line luminosity of the SMGs is 〈L′CO〉= (3.8 ± 2.0) × 1010 K km s‐1 pc2. Using a CO‐to‐H2 conversion factor appropriate for starburst galaxies, this corresponds to a molecular gas mass 〈M(H2)〉= (3.0 ± 1.6) × 1010 M⊙ within an ∼ 2 kpc radius, approximately 4 times greater than the most luminous local ultraluminous infrared galaxies (ULIRGs) but comparable to that of the most extreme high‐redshift radio galaxies (HzRGs) and quasi‐sellar objects (QSOs). The median CO FWHM linewidth is broad, 〈FWHM〉= 780 ± 320 km s−1, and the SMGs often have double‐peaked line profiles, indicative of either a merger or a disc. From their median gas reservoirs (∼ 3 × 1010 M⊙) and star formation rates (≳ 700 M⊙ yr−1), we estimate a lower limit on the typical gas‐depletion time‐scale of ≳ 40 Myr in SMGs. This is marginally below the typical age expected for the starbursts in SMGs and suggests that negative feedback processes may play an important role in prolonging the gas consumption time‐scale. We find a statistically significant correlation between the far‐infrared and CO luminosities of the SMGs, which extends the observed correlation for local ULIRGs to higher luminosities and higher redshifts. The non‐linear nature of the correlation implies that SMGs have higher far‐infrared to CO luminosity ratios and possibly higher star formation efficiencies (SFEs), than local ULIRGs. Assuming a typical CO source diameter of θ∼ 0.5 arcsec (D∼ 4 kpc), we estimate a median dynamical mass of 〈Mdyn〉≃ (1.2 ± 1.5) × 1011 M⊙ for the SMG sample. Both the total gas and stellar masses imply that SMGs are very massive systems, dominated by baryons in their central regions. The baryonic and dynamical properties of these systems mirror those of local giant ellipticals and are consistent with numerical simulations of the formation of the most massive galaxies. We have been able to impose a lower limit of ≳ 5 × 10−6 Mpc−3 to the comoving number density of massive galaxies in the redshift range z∼ 2–3.5, which is in agreement with results from recent spectroscopic surveys and the most recent model predictions.

We report subarcsecond resolution IRAM PdBI millimeter CO interferometry of four z $ 2 submillimeter galaxies (SMGs), and sensitive CO(3Y2) flux limits toward three z $ 2 UV/optically selected star-forming galaxies. The new data reveal for the first time spatially resolved CO gas kinematics in the observed SMGs. Two of the SMGs show double or multiple morphologies, with complex, disturbed gas motions. The other two SMGs exhibit CO velocity gradients of $500 km s À1 across 0.2 00 (1.6 kpc) diameter regions, suggesting that the star-forming gas is in compact, rotating disks. Our data provide compelling evidence that these SMGs represent extreme, short-lived ''maximum'' star-forming events in highly dissipative mergers of gas-rich galaxies. The resulting high-mass surface and volume densities of SMGs are similar to those of compact quiescent galaxies in the same redshift range and much higher than those in local spheroids. From the ratio of the comoving volume densities of SMGs and quiescent galaxies in the same mass and redshift ranges, and from the comparison of gas exhaustion timescales and stellar ages, we estimate that the SMG phase duration is about 100 Myr. Our analysis of SMGs and optically/ UV selected high-redshift starforming galaxies supports a ''universal'' Chabrier IMF as being valid over the star-forming history of these galaxies. We find that the 12 CO luminosity to total gas mass conversion factors at z $ 2Y3 are probably similar to those assumed at z $ 0. The implied gas fractions in our sample galaxies range from 20% to 50%.

We present the results from a survey for 12 CO emission in 40 luminous sub-millimetre galaxies (SMGs), with 850-µm fluxes of S 850µm = 4 − 20 mJy, conducted with the Plateau de Bure Interferometer. We detect 12 CO emission in 32 SMGs at z ∼ 1.2 -4.1, including 16 SMGs not previously published. Using multiple 12 CO line (J up = 2-7) observations, we derive a median spectral line energy distribution for luminous SMGs and use this to estimate a mean gas mass of (5.3 ± 1.0) × 10 10 M . We report the discovery of a fundamental relationship between 12 CO FWHM and 12 CO line luminosity in high-redshift starbursts, which we interpret as a natural consequence of the baryon-dominated dynamics within the regions probed by our observations. We use far-infrared luminosities to assess the star-formation efficiency in our SMGs, finding a steepening of the L CO -L FIR relation as a function of increasing 12 CO J up transition. We derive dynamical masses and molecular gas masses, and use these to determine the redshift evolution of the gas content of SMGs, finding that they do not appear to be significantly more gas rich than less vigorously star-forming galaxies at high redshifts. Finally, we collate X-ray observations, and study the interdependence of gas and dynamical properties of SMGs with their AGN activity and supermassive black hole masses (M BH ), finding that SMGs lie significantly below the local M BH -σ relation. We conclude that SMGs represent a class of massive, gas-rich ultraluminous galaxies with somewhat heterogeneous properties, ranging from starbursting disc-like systems with L∼ 10 12 L , to the most highly star-forming mergers in the Universe.

The structure of stationary photodissociation fronts is revisited. H_2 self- shielding is discussed, including the effects of line overlap. We find that line overlap is important for N(H_2) > 10^{20} cm^{-2}. We compute multiline UV pumping models, and compare these with simple analytic approximations for the effects of self-shielding. The overall fluorescent efficiency of the photodissociation front is obtained for different ratios of chi/n_H (where chi characterizes the intensity of the incident UV) and different dust extinction laws. The dust optical depth tau_{pdr} to the point where 50% of the H is molecular is found to be a simple function of a dimensionless quantity phi_0 depending on chi/n_H, the rate coefficient for H_2 formation on grains, and the UV dust opacity. The fluorescent efficiency of the PDR also depends primarily on phi_0 for chi<3000 and n_H<10^4 cm^{-3}; for stronger radiation fields and higher densities radiative and collisional depopulation of vibrationally-excited levels interferes with the radiative cascade. The emission spectrum from the PDR is essentially independent of the color temperature $T_{color}$ of the incident UV for T_{color}>10^4K, but shows some sensitivity to the v-J distribution of newly-formed H_2. The 1-0S(1)/2-1S(1) and 2-1S(1)/6-4Q(1) intensity ratios, the ortho/para ratio, and the rotational temperature in the $v$=1 and $v$=2 levels are computed as functions of the temperature and density, for different values of chi and n_H. We apply our models to the reflection nebula NGC 2023. We are best able to reproduce the observations with models having chi=5000, n_H=10^5 cm^{-3}.Comment: 50 pages, 24 eps figures, uses aaspp4.sty . To appear in Ap.