[en] We present a search for CO emission in a sample of 10 type-2 quasar host galaxies with redshifts of z ≈ 0.1-0.4. We detect CO(J = 1-0) line emission with ≥5σ in the velocity integrated intensity maps of five sources. A sixth source shows a tentative detection at the ∼4.5σ level of its CO(J = 1-0) line emission. The CO emission of all six sources is spatially coincident with the position at optical, infrared, or radio wavelengths. The spectroscopic redshifts derived from the CO(J = 1-0) line are very close to the photometric ones for all five detections except for the tentative detection for which we find a much larger discrepancy. We derive gas masses of ∼(2-16) × 10⁹ M_☉ for the CO emission in the six detected sources, while we constrain the gas masses to upper limits of M_gas ≤ 8 × 10⁹ M_☉ for the four non-detections. These values are of the order or slightly lower than those derived for type-1 quasars. The line profiles of the CO(J = 1-0) emission are rather narrow (∼<300 km s^–1) and single peaked, unveiling no typical signatures for current or recent merger activity, and are comparable to that of type-1 quasars. However, at least one of the observed sources shows a tidal-tail-like emission in the optical that is indicative of an ongoing or past merging event. We also address the problem of detecting spurious ∼5σ emission peaks within the field of view.

[en] We present high angular resolution (0.''5-2.''0) observations of the millimeter continuum and the ¹²CO(J = 3-2), ¹³CO(J = 3-2), ¹³CO(J = 2-1), C¹⁸O(J = 2-1), HCN(J = 3-2), HCO⁺(J = 4-3), and HCO⁺(J = 3-2) line emission in the circumnuclear disk (r ∼< 100 pc) of the prototypical Seyfert 2 galaxy NGC 1068, carried out with the Submillimeter Array. We also include in our analysis new ¹³CO(J = 1-0) and improved ¹²CO(J = 2-1) observations of NGC 1068 at high angular resolution (1.''0-2.''0) and sensitivity, conducted with the Institute de Radioastronomie Millimetrique Plateau de Bure Interferometer. Based on the complex dynamics of the molecular gas emission indicating non-circular motions in the central ∼100 pc, we propose a scenario in which part of the molecular gas in the circumnuclear disk of NGC 1068 is blown radially outward as a result of shocks. This shock scenario is further supported by quite warm (T_kin ≥ 200 K) and dense (n(H₂) ≅ 10⁴ cm^-3) gas constrained from observed molecular line ratios. The HCN abundance in the circumnuclear disk is found to be [HCN]/[¹²CO] ∼ 10^-3.5. This is slightly higher than the abundances derived for Galactic and extragalactic star-forming/starbursting regions. This result lends further support to X-ray-enhanced HCN formation in the circumnuclear disk of NGC 1068 as suggested by earlier studies. The HCO⁺ abundance ([HCO⁺]/[¹²CO] ∼ 10^-5) appears to be somewhat lower than that of Galactic and extragalactic star-forming/starbursting regions. When trying to fit the centimeter-to-millimeter continuum emission by different thermal and non-thermal processes, it appears that electron-scattered synchrotron emission yields the best results while thermal free-free emission seems to overpredict the millimeter continuum emission.

[en] We report the detection of a CO emission line from the submillimeter galaxy (SMG) GN10 in the GOODS-N field. GN10 lacks any counterpart in extremely deep optical and near-IR imaging obtained with the Hubble Space Telescope and ground-based facilities. This is a prototypical case of a source that is extremely obscured by dust, for which it is practically impossible to derive a spectroscopic redshift in the optical/near-IR. Under the hypothesis that GN10 is part of a proto-cluster structure previously identified at z ∼ 4.05 in the same field, we searched for CO[4-3] at 91.4 GHz with the IRAM Plateau de Bure Interferometer, and successfully detected a line. We find that the most likely redshift identification is z = 4.0424 ± 0.0013, based on: (1) the very low chance that the CO line is actually serendipitous from a different redshift; (2) a radio-IR photometric redshift analysis; (3) the identical radio-IR spectral energy distribution, within a scaling factor of 2 other SMGs at the same redshift. The faintness at optical/near-IR wavelengths requires an attenuation of A _V ∼ 5-7.5 mag. This result supports the case that a substantial population of very high-z SMGs exists that had been missed by previous spectroscopic surveys. This is the first time that a CO emission line has been detected for an SMG that is invisible in the optical and near-IR. Our work demonstrates the power of existing and planned facilities for completing the census of star formation and stellar mass in the distant universe by measuring redshifts of the most obscured galaxies through millimeter spectroscopy.

[en] We present observations of the ¹²CO(J = 6–5) line and 686 GHz continuum emission in NGC 253 with the Submillimeter Array at an angular resolution of ∼4″. The ¹²CO(J = 6–5) emission is clearly detected along the disk and follows the distribution of the lower ¹²CO line transitions with little variation of the line ratios. A large velocity gradient analysis suggests a two-temperature model of the molecular gas in the disk, likely dominated by a combination of low-velocity shocks and the disk-wide photodissociation regions. Only marginal ¹²CO(J = 6–5) emission is detected in the vicinity of the expanding shells at the eastern and western edges of the disk. While the eastern shell contains gas even warmer (T_kin > 300 K) than the hot gas component (T_kin = 300 K) of the disk, the western shell is surrounded by gas much cooler (T_kin = 60 K) than the eastern shell but somewhat hotter than the cold gas component of the disk (for similar H₂ and CO column densities), indicative of different (or differently efficient) heating mechansisms. The continuum emission at 686 GHz in the disk agrees well in shape and size with that at lower (sub)millimeter frequencies, exhibiting a spectral index consistent with thermal dust emission. We find dust temperatures of ∼10–30 K and largely optically thin emission. However, our fits suggest a second (more optically thick) dust component at higher temperatures ($T_{\mathrm{d}}><!--\; >\; -->60$ K), similar to the molecular gas. We estimate a global dust mass of ∼10⁶ $M_{\odot <!--\; ???\; -->}$ for the disk, translating into a gas-to-dust mass ratio of a few hundred, consistent with other nearby active galaxies.

[en] We have used the Institut de Radioastronomie Millimétrique (IRAM) Plateau de Bure Interferometer and the Expanded Very Large Array to obtain a high-resolution map of the CO(6-5) and CO(1-0) emission in the lensed, star-forming galaxy SMM J2135–0102 at z = 2.32. The kinematics of the gas are well described by a model of a rotationally supported disk with an inclination-corrected rotation speed, v_rot = 320 ± 25 km s^–1, a ratio of rotational-to-dispersion support of v/σ = 3.5 ± 0.2, and a dynamical mass of (6.0 ± 0.5) × 10¹⁰ M_☉ within a radius of 2.5 kpc. The disk has a Toomre parameter, Q = 0.50 ± 0.15, suggesting that the gas will rapidly fragment into massive clumps on scales of L_J ∼ 400 pc. We identify star-forming regions on these scales and show that they are ∼10 × denser than those in quiescent environments in local galaxies, and significantly offset from the local molecular cloud scaling relations (Larson's relations). The large offset compared to local molecular cloud line-width-size scaling relations implies that supersonic turbulence should remain dominant on scales ∼100× smaller than in the kinematically quiescent interstellar medium (ISM) of the Milky Way, while the molecular gas in SMM J2135 is expected to be ∼50× denser than that in the Milky Way on all scales. This is most likely due to the high external hydrostatic pressure we measure for the ISM, P_tot/k_B ∼ (2 ± 1) × 10⁷ K cm^–3. In such highly turbulent ISM, the subsonic regions of gravitational collapse (and star formation) will be characterized by much higher critical densities, n_crit > = 10⁸ cm^–3, a factor ∼>1000× more than the quiescent ISM of the Milky Way.

[en] We report the detection of the CO J = 1-0 emission line in three near-infrared selected star-forming galaxies at z ∼ 1.5 with the Very Large Array and the Green Bank Telescope. These observations directly trace the bulk of molecular gas in these galaxies. We find H₂ gas masses of 8.3 ± 1.9 x 10¹⁰ M _sun, 5.6 ± 1.4 x 10¹⁰ M_sun, and 1.23 ± 0.34 x 10¹¹ M_sun for BzK-4171, BzK-21000, and BzK-16000, respectively, assuming a conversion α_CO = 3.6 M _sun (K km s^-1 pc²)^-1. We combined our observations with previous CO 2-1 detections of these galaxies to study the properties of their molecular gas. We find brightness temperature ratios between the CO 2-1 and CO 1-0 emission lines of 0.80^+0.35_-0.22, 1.22^+0.61_-0.36, and 0.41^+0.23_-0.13 for BzK-4171, BzK-21000, and BzK-16000, respectively. At the depth of our observations it is not possible to discern between thermodynamic equilibrium or sub-thermal excitation of the molecular gas at J = 2. However, the low temperature ratio found for BzK-16000 suggests sub-thermal excitation of CO already at J = 2. For BzK-21000, a large velocity gradient model of its CO emission confirms previous results of the low excitation of the molecular gas at J = 3. From a stacked map of the CO 1-0 images, we measure a CO 2-1 to CO 1-0 brightness temperature ratio of 0.92^+0.28_-0.19. This suggests that, on average, the gas in these galaxies is thermalized up to J = 2, has star formation efficiencies of ∼100 L _sun (K km s^-1 pc²)^-1, and gas consumption timescales of ∼0.4 Gyr, unlike submillimeter galaxies and quasi-stellar objects at high redshifts.

[en] We present evidence for very high gas fractions and extended molecular gas reservoirs in normal, near-infrared-selected (BzK) galaxies at z ∼ 1.5. Our results are based on multi-configuration CO[2-1] observations obtained at the IRAM Plateau de Bure Interferometer. All six star-forming galaxies observed were detected at high significance. High spatial resolution observations resolve the CO emission in four of them, implying sizes of the gas reservoirs of order of 6-11 kpc and suggesting the presence of ordered rotation. The galaxies have UV morphologies consistent with clumpy, unstable disks, and UV sizes that are consistent with those measured in CO. The star formation efficiencies are homogeneously low within the sample and similar to those of local spirals-the resulting gas depletion times are ∼0.5 Gyr, much higher than what is seen in high-z submillimeter galaxies and quasars. The CO luminosities can be predicted to within 0.15 dex from the observed star formation rates (SFRs) and stellar masses, implying a tight correlation of the gas mass with these quantities. We use new dynamical models of clumpy disk galaxies to derive dynamical masses for our sample. These models are able to reproduce the peculiar spectral line shapes of the CO emission. After accounting for the stellar and dark matter masses, we derive molecular gas reservoirs with masses of (0.4-1.2)x10¹¹ M_sun. The implied conversion (CO luminosity-to-gas mass) factor is very high: α_CO = 3.6 ± 0.8, consistent with a Galactic conversion factor but 4 times higher than that of local ultra-luminous IR galaxies that is typically used for high-redshift objects. The gas mass in these galaxies is comparable to or larger than the stellar mass, and the gas accounts for an impressive 50%-65% of the baryons within the galaxies' half-light radii. We are thus witnessing truly gas-dominated galaxies at z ∼ 1.5, a finding that explains the high specific SFRs observed for z > 1 galaxies. The BzK galaxies can be viewed as scaled-up versions of local disk galaxies, with low-efficiency star formation taking place inside extended, low-excitation gas disks. These galaxies are markedly different than local ULIRGs and high-z submillimeter galaxies and quasars, where higher excitation and more compact gas is found.

[en] We report observations of the CO(2-1) emission of SDSS J1506+54, a compact (r_e ≈ 135 pc) starburst galaxy at z = 0.6. SDSS J1506+54 appears to be forming stars close to the limit allowed by stellar radiation pressure feedback models: the measured L_IR/L^'_CO∼1500 is one of the highest measured for any galaxy. With its compact optical morphology but extended low surface brightness envelope, post-starburst spectral features, high infrared luminosity (L_IR > 10^12.5 L_☉), low gas fraction (M_H2/M_*∼15%), and short gas depletion time (tens of Myr), we speculate that this is a feedback-limited central starburst episode at the conclusion of a major merger. Taken as such, SDSS J1504+54 epitomizes the brief closing stage of a classic model of galaxy growth: we are witnessing a key component of spheroid formation during what we term a ''redline'' starburst.

[en] We report Plateau de Bure Interferometer (PdBI) 1.1 mm continuum imaging toward two extremely red H – [4.5] > 4 (AB) galaxies at z > 3, which we have previously discovered making use of Spitzer SEDS and Hubble Space Telescope CANDELS ultra-deep images of the Ultra Deep Survey field. One of our objects is detected on the PdBI map with a 4.3σ significance, corresponding to S_ν(1.1 mm)=0.78±0.18 mJy. By combining this detection with the Spitzer 8 and 24 μm photometry for this source, and SCUBA2 flux density upper limits, we infer that this galaxy is a composite active galactic nucleus/star-forming system. The infrared (IR)-derived star formation rate is SFR ≈ 200 ± 100 M _☉ yr^–1, which implies that this galaxy is a higher-redshift analogue of the ordinary ultra-luminous infrared galaxies more commonly found at z ∼ 2-3. In the field of the other target, we find a tentative 3.1σ detection on the PdBI 1.1 mm map, but 3.7 arcsec away of our target position, so it likely corresponds to a different object. In spite of the lower significance, the PdBI detection is supported by a close SCUBA2 3.3σ detection. No counterpart is found on either the deep SEDS or CANDELS maps, so, if real, the PdBI source could be similar in nature to the submillimeter source GN10. We conclude that the analysis of ultra-deep near- and mid-IR images offers an efficient, alternative route to discover new sites of powerful star formation activity at high redshifts.

[en] We present a high-resolution (down to 0.''18), multi-transition imaging study of the molecular gas in the z = 4.05 submillimeter galaxy GN20. GN20 is one of the most luminous starburst galaxy known at z>4, and is a member of a rich proto-cluster of galaxies at z = 4.05 in GOODS-North. We have observed the CO 1-0 and 2-1 emission with the Very Large Array (VLA), the CO 6-5 emission with the Plateau de Bure Interferometer, and the 5-4 emission with Combined Array for Research in Millimeter Astronomy. The H₂ mass derived from the CO 1-0 emission is 1.3 x 10¹¹(α/0.8) M_sun. High-resolution imaging of CO 2-1 shows emission distributed over a large area, appearing as partial ring, or disk, of ∼10 kpc diameter. The integrated CO excitation is higher than found in the inner disk of the Milky Way, but lower than that seen in high-redshift quasar host galaxies and low-redshift starburst nuclei. The CO 4-3 integrated line strength is more than a factor of 2 lower than expected for thermal excitation. The excitation can be modeled with two gas components: a diffuse, lower excitation component with a radius ∼4.5 kpc and a filling factor ∼0.5, and a more compact, higher excitation component (radius ∼2.5 kpc, filling factor ∼0.13). The lower excitation component contains at least half the molecular gas mass of the system, depending on the relative conversion factor. The VLA CO 2-1 image at 0.''2 resolution shows resolved, clumpy structure, with a few brighter clumps with intrinsic sizes ∼2 kpc. The velocity field determined from the CO 6-5 emission is consistent with a rotating disk with a rotation velocity of ∼570 km s^-1 (using an inclination angle of 45⁰), from which we derive a dynamical mass of 3 x 10¹¹ M_sun within about 4 kpc radius. The star formation distribution, as derived from imaging of the radio synchrotron and dust continuum, is on a similar scale as the molecular gas distribution. The molecular gas and star formation are offset by ∼1'' from the Hubble Space Telescope I-band emission, implying that the regions of most intense star formation are highly dust obscured on a scale of ∼10 kpc. The large spatial extent and ordered rotation of this object suggests that this is not a major merger, but rather a clumpy disk accreting gas rapidly in minor mergers or smoothly from the proto-intracluster medium. Qualitatively, the kinematic and structural properties of GN20 compare well to the most rapid star formers fed primarily by cold accretion in cosmological hydrodynamic simulations. Conversely, if GN20 is a major, gas-rich merger, then some process has managed to ensure that the star formation and molecular gas distribution has not been focused into one or two compact regions.