Search

We combine molecular gas masses inferred from CO emission in 500 star-forming galaxies (SFGs) between z = 0 and 3, from the IRAM-COLDGASS, PHIBSS1/2, and other surveys, with gas masses derived from Herschel far-IR dust measurements in 512 galaxy stacks over the same stellar mass/redshift range. We constrain the scaling relations of molecular gas depletion timescale (tdepl) and gas to stellar mass ratio (Mmol gas/M∗) of SFGs near the star formation "main-sequence" with redshift, specific star-formation rate (sSFR), and stellar mass (M∗). The CO- and dust-based scaling relations agree remarkably well. This suggests that the CO → H2 mass conversion factor varies little within ±0.6 dex of the main sequence (sSFR(ms, z, M∗)), and less than 0.3 dex throughout this redshift range. This study builds on and strengthens the results of earlier work. We find that tdepl scales as (1 + z)-0.3 × (sSFR/sSFR(ms, z, M∗))-0.5, with little dependence on M∗. The resulting steep redshift dependence of Mmol gas/M∗≈ (1 + z)3 mirrors that of the sSFR and probably reflects the gas supply rate. The decreasing gas fractions at high M∗are driven by the flattening of the SFR-M∗relation. Throughout the probed redshift range a combination of an increasing gas fraction and a decreasing depletion timescale causes a larger sSFR at constant M∗. As a result, galaxy integrated samples of the Mmol gas-SFR rate relation exhibit a super-linear slope, which increases with the range of sSFR. With these new relations it is now possible to determine Mmol gas with an accuracy of ±0.1 dex in relative terms, and ±0.2 dex including systematic uncertainties.

We report matched resolution imaging spectroscopy of the CO 3-2 e (with the IRAM Plateau de Bure millimeter interferometer) and of the Hα e (with LUCI at the Large Binocular Telescope) in the massive z = 1.53 main-sequence galaxy EGS 13011166, as part of the "Plateau de Bure high-z, blue-sequence survey" (PHIBSS: Tacconi et al.). We combine these data with Hubble Space Telescope V-I-J-H-band maps to derive spatially resolved distributions of stellar surface density, star formation rate, molecular gas surface density, optical extinction, and gas kinematics. The spatial distribution and kinematics of the ionized and molecular gas are remarkably similar and are well modeled by a turbulent, globally Toomre unstable, rotating disk. The stellar surface density distribution is smoother than the clumpy rest-frame UV/optical light distribution and peaks in an obscured, star-forming massive bulge near the dynamical center. The molecular gas surface density and the effective optical screen extinction track each other and are well modeled by a "mixed" extinction model. The inferred slope of the spatially resolved molecular gas to star formation rate relation, N = dlogΣstar form/dlogΣmol gas, depends strongly on the adopted extinction model, and can vary from 0.8 to 1.7. For the preferred mixed dust-gas model, we find N = 1.14 ± 0.1. © 2013. The American Astronomical Society. All rights reserved.

We present the results of a survey of CO(1−0) emission in 14 infrared luminous dusty star-forming galaxies (DSFGs) at 2 < z < 4 with the NSF's Karl G. Jansky Very Large Array. All sources are detected in 12CO(1−0), with an angular resolution of ∼1″. Seven sources show extended and complex structure. We measure CO luminosities of (μ) L CO (1 − 0) ′ = 0.4 – 2.9 × 10 11 K km s−1 pc2, and molecular gas masses of (μ) M H 2 = 1.3 – 8.6 × 10 11 M ⊙, where (μ) is the magnification factor. The derived molecular gas depletion times of t dep = 40–460 Myr, cover the expected range of both normal star-forming galaxies and starbursts. Compared to the higher − J CO transitions previously observed for the same sources, we find CO temperature brightness ratios of r 32/10 = 0.4–1.4, r 43/10 = 0.4–1.7, and r 54/10 = 0.3–1.3. We find a wide range of CO spectral line energy distributions (SLEDs), in agreement with other high- z DSFGs, with the exception of three sources that are most comparable to Cloverleaf and APM08279+5255. Based on radiative transfer modeling of the CO SLEDs we determine densities of n H 2 = 0.3 − 8.5 × 10 3 cm−3 and temperatures of T K = 100–200 K. Lastly, four sources are detected in the continuum, three have radio emission consistent with their infrared-derived star formation rates, while HerBS-70E requires an additional synchrotron radiation component from an active galactic nucleus. Overall, we find that even though the sample is similarly luminous in the infrared, by tracing the CO(1−0) emission a diversity of galaxy and excitation properties are revealed, demonstrating the importance of CO(1−0) observations in combination to higher- J transitions. [ABSTRACT FROM AUTHOR]

We report high-quality, Hα or CO rotation curves (RCs) to several Re for 41 large, massive, star-forming disk galaxies (SFGs) across the peak of cosmic galaxy evolution (z ∼ 0.67–2.45), taken with the ESO-VLT, the LBT and IRAM-NOEMA. Most RC41 SFGs have reflection-symmetric RCs plausibly described by equilibrium dynamics. We fit the major axis position–velocity cuts using beam-convolved forward modeling generated in three dimensions, with models that include a bulge and turbulent disk component embedded in a dark matter (DM) halo. We include priors for stellar and molecular gas masses, optical light effective radii and inclinations, and DM masses from abundance-matching scaling relations. Two-thirds or more of the z ≥ 1.2 SFGs are baryon dominated within a few Re of typically 5.5 kpc and have DM fractions less than maximal disks (median). At lower redshift (z < 1.2), that fraction is less than one-third. DM fractions correlate inversely with the baryonic angular momentum parameter, baryonic surface density, and bulge mass. Inferred low DM fractions cannot apply to the entire disk and halo but more plausibly reflect a flattened, or cored, inner DM density distribution. The typical central "DM deficit" in these cores relative to Navarro–Frenk–White (NFW) distributions is ∼30% of the bulge mass. The observations are consistent with rapid radial transport of baryons in the first-generation massive gas-rich halos forming globally gravitationally unstable disks and leading to efficient build-up of massive bulges and central black holes. A combination of heating due to dynamical friction and AGN feedback may drive DM out of the initial cusps. [ABSTRACT FROM AUTHOR]

We present observations of SO and SO2 lines toward the shocked regions along the L1157 chemically rich outflow, taken in the context of the Seeds of Life in Space IRAM Northern Extended Millimeter Array Large Program, and supported by data from the Submillimeter Array and IRAM-30 m telescope at 1.1–3.6 mm wavelengths. We simultaneously analyze, for the first time, all of the brightest shocks in the blueshifted lobe, namely, B0, B1, and B2. We found the following. (1) SO and SO2 may trace different gas, given that the large(-scale) velocity gradient analysis indicates for SO2 a volume density () denser than that of the gas emitting in SO by a factor up to an order of magnitude. (2) Investigating the 0.1 pc scale field of view, we note a tentative gradient along the path of the precessing jet. More specifically, decreases from the B0–B1 shocks to the older B2. (3) At a linear resolution of 500–1400 au, a tentative spatial displacement between the two emitting molecules is detected, with the SO peak closer (with respect to SO2) to the position where the recent jet is impinging on the B1 cavity wall. Our astrochemical modeling shows that the SO and SO2 abundances evolve on timescales less than about 1000 years. Furthermore, the modeling requires high abundances (2 × 10−6) of both and S/H injected in the gas phase due to the shock occurrence, so prefrozen OCS only is not enough to reproduce our new observations. [ABSTRACT FROM AUTHOR]

We present direct constraints on the CO luminosity function at high redshift and the resulting cosmic evolution of the molecular gas density, (z), based on a blind molecular line scan in the Hubble Deep Field North (HDF-N) using the IRAM Plateau de Bure Interferometer. Our line scan of the entire 3 mm window (79-115 GHz) covers a cosmic volume of ∼7000 Mpc3, and redshift ranges z < 0.45, 1.01 < z < 1.89 and z > 2. We use the rich multiwavelength and spectroscopic database of the HDF-N to derive some of the best constraints on CO luminosities in high redshift galaxies to date. We combine the blind CO detections in our molecular line scan (presented in a companion paper) with stacked CO limits from galaxies with available spectroscopic redshifts (slit or mask spectroscopy from Keck and grism spectroscopy from the Hubble Space Telescope) to give first blind constraints on high-z CO luminosity functions and the cosmic evolution of the H2 mass density (z) out to redshifts z ∼ 3. A comparison to empirical predictions of (z) shows that the securely detected sources in our molecular line scan already provide significant contributions to the predicted (z) in the redshift bins 〈 z〉 ∼ 1.5 and 〈 z〉 ∼ 2.7. Accounting for galaxies with CO luminosities that are not probed by our observations results in cosmic molecular gas densities (z) that are higher than current predictions. We note, however, that the current uncertainties (in particular the luminosity limits, number of detections, as well as cosmic volume probed) are significant, a situation that is about to change with the emerging ALMA observatory. [ABSTRACT FROM AUTHOR]

We present a molecular line scan in the Hubble Deep Field North (HDF-N) that covers the entire 3 mm window (79-115 GHz) using the IRAM Plateau de Bure Interferometer. Our CO redshift coverage spans z ≲ 0.45, 1 ≲ z ≲ 1.9 and all z ≳ 2. We reach a CO detection limit that is deep enough to detect essentially all z > 1 CO lines reported in the literature so far. We have developed and applied different line-searching algorithms, resulting in the discovery of 17 line candidates. We estimate that the rate of false positive line detections is ∼2/17. We identify optical/NIR counterparts from the deep ancillary database of the HDF-N for seven of these candidates and investigate their available spectral energy distributions. Two secure CO detections in our scan are identified with star-forming galaxies at z = 1.784 and at z = 2.047. These galaxies have colors consistent with the “BzK” color selection and they show relatively bright CO emission compared with galaxies of similar dust continuum luminosity. We also detect two spectral lines in the submillimeter galaxy HDF 850.1 at z = 5.183. We consider an additional nine line candidates as high quality. Our observations also provide a deep 3 mm continuum map (1σ noise level = 8.6 μJy beam–1). Via a stacking approach, we find that optical/MIR bright galaxies contribute only to <50% of the star formation rate density at 1 < z < 3, unless high dust temperatures are invoked. The present study represents a first, fundamental step toward an unbiased census of molecular gas in “normal” galaxies at high-z, a crucial goal of extragalactic astronomy in the ALMA era. [ABSTRACT FROM AUTHOR]

Panchromatic observations of the best candidate hyperluminous infrared galaxies from the widest Herschel extragalactic imaging survey have led to the discovery of at least four intrinsically luminous z = 2.41 galaxies across an ≈100 kpc region—a cluster of starbursting protoellipticals. Via subarcsecond interferometric imaging we have measured accurate gas and star formation surface densities. The two brightest galaxies span ~3 kpc FWHM in submillimeter/radio continuum and CO J = 4-3, and double that in CO J = 1-0. The broad CO line is due partly to the multitude of constituent galaxies and partly to large rotational velocities in two counter-rotating gas disks—a scenario predicted to lead to the most intense starbursts, which will therefore come in pairs. The disks have Mdyn of several ×1011 M⊙, and gas fractions of ~40%. Velocity dispersions are modest so the disks are unstable, potentially on scales commensurate with their radii: these galaxies are undergoing extreme bursts of star formation, not confined to their nuclei, at close to the Eddington limit. Their specific star formation rates place them ≳5× above the main sequence, which supposedly comprises large gas disks like these. Their high star formation efficiencies are difficult to reconcile with a simple volumetric star formation law. N-body and dark matter simulations suggest that this system is the progenitor of a B(inary)-type ≈1014.6-M⊙ cluster. [ABSTRACT FROM AUTHOR]

We present PHIBSS, the IRAM Plateau de Bure high-z blue sequence CO 3-2 survey of the molecular gas properties in massive, main-sequence star-forming galaxies (SFGs) near the cosmic star formation peak. PHIBSS provides 52 CO detections in two redshift slices at z ~ 1.2 and 2.2, with log(M"(M☉)) ⩾ 10.4 and log(SFR(M☉/yr)) ⩾ 1.5. Including a correction for the incomplete coverage of the M"-SFR plane, and adopting a "Galactic" value for the CO-H2 conversion factor, we infer average gas fractions of ~0.33 at z ~ 1.2 and ~0.47 at z ~ 2.2. Gas fractions drop with stellar mass, in agreement with cosmological simulations including strong star formation feedback. Most of the z ~ 1-3 SFGs are rotationally supported turbulent disks. The sizes of CO and UV/optical emission are comparable. The molecular-gas-star-formation relation for the z = 1-3 SFGs is near-linear, with a ~0.7 Gyr gas depletion timescale; changes in depletion time are only a secondary effect. Since this timescale is much less than the Hubble time in all SFGs between z ~ 0 and 2, fresh gas must be supplied with a fairly high duty cycle over several billion years. At given z and M", gas fractions correlate strongly with the specific star formation rate (sSFR). The variation of sSFR between z ~ 0 and 3 is mainly controlled by the fraction of baryonic mass that resides in cold gas. [ABSTRACT FROM AUTHOR]

We use the first systematic samples of CO millimeter emission in z ≥ 1 "main-sequence" star-forming galaxies to study the metallicity dependence of the conversion factor αCO, from CO line luminosity to molecular gas mass. The molecular gas depletion rate inferred from the ratio of the star formation rate (SFR) to CO luminosity, is ~1 Gyr-1 for near-solar metallicity galaxies with stellar masses above Ms ~ 101l M⊙. In this regime, the depletion rate does not vary more than a factor of two to three as a function of molecular gas surface density or redshift between z ~ 0 and 2. Below Ms the depletion rate increases rapidly with decreasing metallicity. We argue that this trend is not caused by starburst events, by changes in the physical parameters of the molecular clouds, or by the impact of the fundamental-metallicity-SFR-stellar mass relation. A more probable explanation is that the conversion factor is metallicity dependent and that star formation can occur in "CO-dark" gas. The trend is also expected theoretically from the effect of enhanced photodissociation of CO by ultraviolet radiation at low metallicity. From the available z ~ 0 and z ~ 1-3 samples we constrain the slope of the log(αCO)-log (metallicity) relation to range between -1 and -2, fairly insensitive to the assumed slope of the gas-SFR relation. Because of the lower metallicities near the peak of the galaxy formation activity at z ~ 1-2 compared to z ~ 0, we suggest that molecular gas masses estimated from CO luminosities have to be substantially corrected upward for galaxies below Ms. [ABSTRACT FROM AUTHOR]

We report ground-based follow-up observations of the exceptional source, ID 141, one of the brightest sources detected so far in the Herschel Astrophysical Terahertz Large Area Survey cosmological survey. ID 141 was observed using the IRAM 30 m telescope and Plateau de Bure interferometer (PdBI), the Submillimeter Array, and the Atacama Pathfinder Experiment submillimeter telescope to measure the dust continuum and emission lines of the main isotope of carbon monoxide and carbon ([C I] and [C II]). The detection of strong CO emission lines with the PdBI confirms that ID 141 is at high redshift (ɀ = 4.243 ± 0.001). The strength of the continuum and emission lines suggests that ID 141 is gravitationally lensed. The width (ΔVFWHM ∼ 800 km s-1) and asymmetric profiles of the CO and carbon lines indicate orbital motion in a disk or a merger. The properties derived for ID 141 are compatible with an ultraluminous (LFIR ∼ (8.5 ± 0.3) x 1013 Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. Lʘ, where μL is the amplification factor), dense (n ≈ 104 cm-3), and warm (Tkin ≈ as 40 K) starburst galaxy, with an estimated star formation rate of (0.7-1.7) x 104 Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed. Mʘ yr-1. The carbon emission lines indicate a dense (n ≈ 104 cm-3) photon-dominated region, illuminated by a far-UV radiation field a few thousand times more intense than that in our Galaxy. In conclusion, the physical properties of the high-ɀ galaxy ID 141 are remarkably similar to those of local ultraluminous infrared galaxies. [ABSTRACT FROM AUTHOR]

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), C180(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 (Tkin ≥ 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. [ABSTRACT FROM AUTHOR]

We present the results of interferometric spectral line observations of Arp 220 at 3.5 mm and 1.2 mm from the Plateau de Bure Interferometer, imaging the two nuclear disks in H13CN(1-0) and (3-2), H13CO+(1-0) and (3-2), and HN13C(3-2) as well as SiO(2-1) and (6-5), HC15N(3-2), and SO(66-55). The gas traced by SiO(6-5) has a complex and extended kinematic signature including a prominent P Cygni profile, almost identical to previous observations of HCO+(3-2). Spatial offsets 0.″1 north and south of the continuum center in the emission and absorption of the SiO(6-5) P Cygni profile in the western nucleus (WN) imply a bipolar outflow, delineating the northern and southern edges of its disk and suggesting a disk radius of ∼40 pc, consistent with that found by ALMA observations of Arp 220. We address the blending of SiO(6-5) and H13CO+(3-2) by considering two limiting cases with regards to the H13CO+ emission throughout our analysis. Large velocity gradient modeling is used to constrain the physical conditions of the gas and to infer abundance ratios in the two nuclei. Our most conservative lower limit on the [H13CN]/[H13CO+] abundance ratio is 11 in the WN, compared with 0.10 in the eastern nucleus (EN). Comparing these ratios to the literature we argue on chemical grounds for an energetically significant active galactic nucleus in the WN driving either X-ray or shock chemistry, and a dominant starburst in the EN. [ABSTRACT FROM AUTHOR]

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) × 109M☼ for the CO emission in the six detected sources, while we constrain the gas masses to upper limits of Mgas ⩽ 8 × 109M☼ 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. [ABSTRACT FROM AUTHOR]

We present a search for the [C II] 158 μm fine structure line (a main cooling line of the interstellar medium) and the underlying far-infrared (FIR) continuum in three high-redshift (6.6 < z < 8.2) star-forming galaxies using the IRAM Plateau de Bure Interferometer. We targeted two Lyα-selected galaxies (Lyα emitters, LAEs) with moderate UV-based star formation rates (SFRs ∼ 20 M☼ yr–1; Himiko at z = 6.6 and IOK-1 at z = 7.0) and a gamma-ray burst (GRB) host galaxy (GRB 090423 at z ∼ 8.2). Based on our 3σ rest-frame FIR continuum limits, previous (rest-frame) UV continuum measurements and spectral energy distribution (SED) fitting, we rule out SED shapes similar to highly obscured galaxies (e.g., Arp 220, M 82) and less extreme dust-rich nearby spiral galaxies (e.g., M 51) for the LAEs. Conservatively assuming an SED shape typical of local spiral galaxies we derive upper limits for the FIR-based star formation rates (SFRs) of ∼70 M☼ yr–1, ∼50 M☼ yr–1, and ∼40 M☼ yr–1 for Himiko, IOK-1, and GRB 090423, respectively. For the LAEs these limits are only a factor ∼3 higher than the published UV-based SFRs (uncorrected for extinction). This indicates that the dust obscuration in the z > 6 LAEs studied here is lower by a factor of a few than what has recently been found in some LAEs at lower redshift (2 < z < 3.5) with similar UV-based SFRs. A low obscuration in our z > 6 LAE sample is consistent with recent rest-frame UV studies of z ∼ 7 Lyman break galaxies. [ABSTRACT FROM AUTHOR]

We present secure [N II]205 μm detections in two millimeter-bright, strongly lensed objects at high redshift, APM 08279+5255 (z = 3.911) and MM 18423+5938 (z = 3.930), using the IRAM Plateau de Bure Interferometer. Due to its ionization energy [N II]205 μm is a good tracer of the ionized gas phase in the interstellar medium. The measured fluxes are S([N II]205 μm) = (4.8 ± 0.8) Jy km s–1 and (7.4 ± 0.5) Jy km s–1, respectively, yielding line luminosities of L([N II]205 μm) = (1.8 ± 0.3) × 109 μ–1L☼ for APM 08279+5255 and L([N II]205 μm) = (2.8 ± 0.2) × 109 μ–1L☼ for MM 18423+5938. Our high-resolution map of the [N II]205 μm and 1 mm continuum emission in MM 18423+5938 clearly resolves an Einstein ring in this source and reveals a velocity gradient in the dynamics of the ionized gas. A comparison of these maps with high-resolution EVLA CO observations enables us to perform the first spatially resolved study of the dust continuum-to-molecular gas surface brightness (ΣFIR∝ΣNCO, which can be interpreted as the star formation law) in a high-redshift object. We find a steep relation (N = 1.4 ± 0.2), consistent with a starbursting environment. We measure a [N II]205 μm/FIR luminosity ratio in APM 08279+5255 and MM 18423+5938 of 9.0 × 10–6 and 5.8 × 10–6, respectively. This is in agreement with the decrease of the [N II]205 μm/FIR ratio at high FIR luminosities observed in local galaxies. [ABSTRACT FROM AUTHOR]