Large Gas Reservoirs Research Articles

Physical conditions in Centaurus A’s northern filaments

NGC 5128 (Centaurus A) is one of the best targets to study AGN-feedback in the local Universe. Optical filaments located at 16 kpc from the galaxy along the radio jet direction show recent star formation, likely triggered by the interaction of the jet with an H I shell. A large reservoir of molecular gas has been discovered outside the H I. In this reservoir, lies the Horseshoe complex: a filamentary structure seen in CO with ALMA and in Hα with MUSE. The ionised gas is mostly excited by shocks, with only a minor contribution of star formation. We used the Atacama Pathfinder EXperiment (APEX) to observe the 12CO(3-2) and 12CO(4-3) transitions, as well as dense gas tracers in the Horseshoe complex. 12CO(3-2) and 12CO(4-3) are detected for the first time in the northern filaments of Centaurus A, with integrated intensity line ratios R32 ∼ 0.2 and R43 ∼ 0.1, compared to the 12CO(1-0) emission. We also derived a line ratio R21 ∼ 0.6, based on previous 12CO(2-1) observations. We used the non-LTE radiative transfer code RADEX and determined that the molecular gas in this region has a temperature of 55−70 K and densities between 2−6 × 102 cm−3. Such densities are also in agreement with results from the Paris-Durham shock code that predicts a post-shock density of a few 100 cm−3. However, we need more observations of emission lines at a better angular resolution in order to place tighter constraints on our radiative models, whether they are used as a stand-alone tool (LVG codes) or combined with a shock model.

Characteristics and Mechanism of Upper Permian Reef Reservoirs in the Eastern Longgang Area, Northeastern Sichuan Basin, China

Abstract As a typical kind of lithologic reservoirs, reef reservoirs are generally featured by their large single-well reservoir thickness, good reservoir physical properties, and high gas well productivity. The Upper Permian Changxing Formation is an important natural gas exploration target in the Sichuan Basin, which hosts a large reef gas reservoir and is mainly distributed along the Kaijiang-Liangping Trough. Comprehensive analyses are implemented to investigate reservoir characteristics and identify controlling factors of reef reservoirs in Changxing Formation in the Eastern Longgang Area, Northeastern Sichuan Basin, including core, logging, and seismic data analyses. Changxing Formation reservoirs in the study area mainly occur in the reef-shoal complex, which are featured by wide distribution, large thickness and generally good physical properties. Reservoir rocks are dominantly composed of bioclastic dolomite and silty-fine dolomite (with grain phantom structure), while the main reservoir space consists of residual intergranular pores, intergranular dissolution pores, and karst vugs. In the seismic profiles, typical mound-shaped chaotic reflections can be clearly seen. It is suggested by the main reservoir development controlling factor analysis that the distributions of reef reservoirs are typically controlled by sedimentary facies belts, while the scale of the reef-shoal complex is determined by the pene-sedimentary micro-paleo-geomorphology. Dolomitization can not only significantly preserve the primary pores but also enhance the permeability of rocks. Moreover, karstification is the key to high-quality reef-shoal reservoirs.

Reconciling the Long‐Term Relationship Between Reservoir Pore Pressure Depletion and Compaction in the Groningen Region

AbstractThe Groningen gas reservoir, situated in the northeast of the Netherlands is western Europe's largest gas reservoir. Due to gas production measurable subsidence and seismicity has been detected across this region, attributed to the deformations induced by reservoir pore pressure depletion. We investigate the surface displacement history using a principal component analysis‐based inversion method to combine a diverse set of optical leveling, interferometric synthetic aperture radar, and Global Positioning System data to better constrain reservoir compaction and subsidence history. The generated compaction model is then used in combination with prior pressure depletion models to determine a reservoir uniaxial compressibility. The best fitting model of uniaxial compressibility is time independent but spatially variable. The absence of evidence for any significant time delay between changes in depletion and compaction rates supports an instantaneous poroelastic reservoir response. The absence of nonlinear yielding at the largest compaction strains suggests that anelastic deformations are a minor part of reservoir compaction.

Large reservoirs of turbulent diffuse gas around high-z starburst galaxies

AbstractStarburst galaxies at z ∼ 2 – 4 are among the most intensely star-forming galaxies in the universe. The way they accrete their gas to form stars at such high rates is still a controversial issue. ALMA has detected the CH+ (J = 1-0) line in emission and/or absorption in all the gravitationally lensed starburst galaxies targeted so far at z ∼ 3. Its unique spectroscopic and chemical properties enable CH+ to highlight the sites of most intense dissipation of mechanical energy. The absorption lines reveal highly turbulent, massive reservoirs of low-density molecular gas. The broad emission lines, arising in myriad UV-irradiated molecular shocks, reveal powerful galactic winds. The CH+ lines therefore probe the fate of prodigious energy releases, due to infall and/or outflows, and primarily stored in turbulence before being radiated by cool molecular gas. The turbulent reservoirs act as mass and energy buffers over the duration of the starburst phase.

ALMA reveals large molecular gas reservoirs in recently-quenched galaxies

AbstractWe still do not understand the physical mechanisms that are responsible for suppressing star formation in galaxies. Observations of post-starburst galaxies, whose spectra indicate that an intense period of star formation was followed by rapid quenching, are the ideal sample to probe the quenching process. We have conducted an ALMA survey of CO(2-1) in 13 of these recently- quenched galaxies at z ∼ 0.7 – high enough redshift that these galaxies likely just concluded their primary epoch of star formation, but low enough redshift for follow-up observations to be feasible. Our observations reveal a stunning diversity of molecular gas properties: despite a uniform optical selection and low apparent SFRs, the detected galaxies span a factor of > 30 in CO luminosity and have inferred gas fractions ranging from < 1% to 20%. These observations indicate that quenching does not require the total removal or depletion of molecular gas. No current models of the quenching process can fully explain our results.

Asgard archaea capable of anaerobic hydrocarbon cycling

Large reservoirs of natural gas in the oceanic subsurface sustain complex communities of anaerobic microbes, including archaeal lineages with potential to mediate oxidation of hydrocarbons such as methane and butane. Here we describe a previously unknown archaeal phylum, Helarchaeota, belonging to the Asgard superphylum and with the potential for hydrocarbon oxidation. We reconstruct Helarchaeota genomes from metagenomic data derived from hydrothermal deep-sea sediments in the hydrocarbon-rich Guaymas Basin. The genomes encode methyl-CoM reductase-like enzymes that are similar to those found in butane-oxidizing archaea, as well as several enzymes potentially involved in alkyl-CoA oxidation and the Wood-Ljungdahl pathway. We suggest that members of the Helarchaeota have the potential to activate and subsequently anaerobically oxidize hydrothermally generated short-chain hydrocarbons.

Hydrocarbon generation characteristics and exploration prospects of Proterozoic source rocks in China

A large number of primary oil and gas reservoirs have been discovered in Proterozoic strata all over the globe. Proterozoic sequences are widely distributed in China, and the discovery of large Sinian-aged gas reservoirs in the Sichuan Basin and Mesoproterozoic liquid oil seepages in North China shows that attention should be paid to the exploration potential of Proterozoic strata. In this paper, the main controlling factors of Proterozoic source rocks are discussed. Principally, active atmospheric circulation and astronomical cycles may have driven intense upwelling and runoff to provide nutrients; oxygenated oceanic surface waters could have provided suitable environments for the organisms to thrive; volcanic activity and terrestrial weathering caused by continental break-up would have injected large amounts of nutrients into the ocean, leading to persistent blooms of marine organisms; and extensive anoxic deep waters may have created ideal conditions for the preservation of organic matter. Additionally, the appearance of eukaryotes resulted in diversified hydrocarbon parent material, which effectively improved the generation potential for oil and gas. Through the comparison of Formations across different cratons, seven sets of Proterozoic organic-rich source rocks have been recognized in China, which mainly developed during interglacial periods and are also comparable worldwide. The Hongshuizhuang and Xiamaling Formations in North China have already been identified previously as Mesoproterozoic source rocks. The early Proterozoic Changchengian System is highly promising as a potential source rock in the Ordos Basin. In the Upper Yangtze area, the Neoproterozoic Datangpo and Doushantuo Formations are extensively distributed, and represent the major source rocks for Sinian gas reservoirs in the Sichuan Basin. Moreover, the Nanhuan System may contain abundant shales with high organic matter contents in the Tarim Basin, although this possibility still needs to be verified. Indeed, all three cratons may contain source rocks of Proterozoic strata; thus, these strata represent major exploration targets worthy of great attention.

Evolution of the cold gas properties of simulated post-starburst galaxies

Abstract Post-starburst galaxies are typically considered to be a transition population, en route to the red sequence after a recent quenching event. Despite this, recent observations have shown that these objects typically have large reservoirs of cold molecular gas. In this paper we study the star-forming gas properties of a large sample of post-starburst galaxies selected from the cosmological, hydrodynamical EAGLE simulations. These objects resemble observed high-mass post-starburst galaxies both spectroscopically and in terms of their space density, stellar mass distribution, and sizes. We find that the vast majority of simulated post-starburst galaxies have significant gas reservoirs, with star-forming gas masses ≈109 M⊙, in good agreement with those seen in observational samples. The simulation reproduces the observed time evolution of the gas fraction of the post-starburst galaxy population, with the average galaxy losing ≈90 per cent of its star-forming interstellar medium in only ≈600 Myr. A variety of gas consumption/loss processes are responsible for this rapid evolution, including mergers and environmental effects, while active galactic nuclei play only a secondary role. The fast evolution in the gas fraction of post-starburst galaxies is accompanied by a clear decrease in the efficiency of star formation due to a decrease in the dense gas fraction. We predict that forthcoming ALMA observations of the gas reservoirs of low-redshift post-starburst galaxies will show that the molecular gas is typically compact and has disturbed kinematics, reflecting the disruptive nature of many of the evolutionary pathways that build up the post-starburst galaxy population.

Characterising the high-mass star forming filament G351.776–0.527 with Herschel and APEX dust continuum and gas observations

G351.776-0.527 is among the most massive, closest, and youngest filaments in the inner Galactic plane and therefore it is an ideal laboratory to study the kinematics of dense gas and mass replenishment on a large scale. In this paper, we present far-infrared and submillimetre wavelength continuum observations combined with spectroscopic C18O (2–1) data of the entire region to study its temperature, mass distribution, and kinematics. The structure is composed of a main elongated region with an aspect ratio of ~23, which is associated with a network of filamentary structures. The main filament has a remarkably constant width of 0.2 pc. The total mass of the network (including the main filament) is ≥2600M⊙, while we estimate a mass of ~2000M⊙ for the main structure. Therefore, the network harbours a large reservoir of gas and dust that could still be accreted onto the main structure. From the analysis of the gas kinematics, we detect two velocity components in the northern part of the main filament. The data also reveal velocity oscillations in C18O along the spine in the main filament and in at least one of the branches. Considering the region as a single structure, we find that it is globally close to virial equilibrium indicating that the entire structure is approximately in a stable state.

Nearly all the sky is covered by Lyman-α emission around high-redshift galaxies.

Galaxies are surrounded by large reservoirs of gas, mostly hydrogen, that are fed by inflows from the intergalactic medium and by outflows from galactic winds. Absorption-line measurements along the lines of sight to bright and rare background quasars indicate that this circumgalactic medium extends far beyond the starlight seen in galaxies, but very little is known about its spatial distribution. The Lyman-α transition of atomic hydrogen at a wavelength of 121.6 nanometres is an important tracer of warm (about 104 kelvin) gas in and around galaxies, especially at cosmological redshifts greater than about 1.6 at which the spectral line becomes observable from the ground. Tracing cosmic hydrogen through its Lyman-α emission has been a long-standing goal of observational astrophysics1-3, but the extremely low surface brightness of the spatially extended emission is a formidable obstacle. A new window into circumgalactic environments was recently opened by the discovery of ubiquitous extended Lyman-α emission from hydrogen around high-redshift galaxies4,5. Such measurements were previously limited to especially favourable systems6-8 or to the use of massive statistical averaging9,10 because of the faintness of this emission. Here we report observations of low-surface-brightness Lyman-α emission surrounding faint galaxies at redshifts between 3 and 6. We find that the projected sky coverage approaches 100 per cent. The corresponding rate of incidence (the mean number of Lyman-α emitters penetrated by any arbitrary line of sight) is well above unity and similar to the incidence rate of high-column-density absorbers frequently detected in the spectra of distant quasars11-14. This similarity suggests that most circumgalactic atomic hydrogen at these redshifts has now been detected in emission.

Why Post-starburst Galaxies Are Now Quiescent

Abstract Post-starburst or “E + A” galaxies are rapidly transitioning from star-forming to quiescence. While the current star formation rate (SFR) of post-starbursts is already at the level of early-type galaxies, we recently discovered that many have large CO-traced molecular gas reservoirs consistent with normal star-forming galaxies. These observations raise the question of why these galaxies have such low SFRs. Here we present an ALMA search for the denser gas traced by HCN (1–0) and HCO+ (1–0) in two CO-luminous, quiescent post-starburst galaxies. Intriguingly, we fail to detect either molecule. The upper limits are consistent with the low SFRs and with early-type galaxies. The HCN/CO luminosity ratio upper limits are low compared to star-forming and even many early-type galaxies. This implied low dense gas mass fraction explains the low SFRs relative to the CO-traced molecular gas and suggests that the state of the gas in post-starburst galaxies is unusual, with some mechanism inhibiting its collapse to denser states. We conclude that post-starbursts galaxies are now quiescent because little dense gas is available, in contrast to the significant CO-traced lower density gas reservoirs that still remain.

Nonisothermal reservoir/wellbore flow modeling in gas reservoirs

Most analytical and numerical flow modeling presuppose isothermal flow behavior in the reservoir. However, for high rates and large consequent drawdown gas reservoirs, the nonisothermal behavior becomes the norm due to the Joule-Thomson (J-T) effect. Other factors, such as a fluid's adiabatic expansion (AE), heat convection, and the heat exchange with surrounding formations may also make contributions. Accounting for this nonisothermal flow behavior becomes a necessity for accurately estimating a well's performance due to changes in fluid properties.This paper starts with the general energy balance in the reservoir and presents a semianalytical solution to estimate the nonisothermal, single-phase gas temperature in the reservoir during production. This solution considers the J-T effect, adiabatic expansion effect, transient temperature behavior, heat convection, and heat exchange of fluid with over and under-burden formation. The variations of gas viscosity, density, J-T coefficient as a function of temperature and pressure are taken into consideration by making a small spatial step at each computational node. A field case study validates the time-variant wellbore temperature profiles with the coupled reservoir heat-transfer model. Distributed temperature measurements or DTS during a drillstem test (DST) made this validation feasible.The J-T effect dominates in the near wellbore region due to dramatic pressure change. The J-T induced cooling usually occurs for gas in the reservoir. However, for high-pressure systems, the gas behaves like a liquid and gets heated up. For some intermediate pressure intervals, the gas temperature slightly increases with expansion, reach a plateau, and then gradually decreases as the gas moves toward the wellbore with declining pressure. By coupling the reservoir heat-transfer model with the wellbore heat-transfer model, one can monitor more accurately.

Massive, Absorption-selected Galaxies at Intermediate Redshifts

Abstract The nature of absorption-selected galaxies and their connection to the general galaxy population have been open issues for more than three decades, with little information available on their gas properties. Here we show, using detections of carbon monoxide emission with the Atacama Large Millimeter/submillimeter Array, that five of seven high-metallicity, absorption-selected galaxies at intermediate redshifts, z ≈ 0.5–0.8, have large molecular gas masses, M Mol ≈ (0.6–8.2) × 1010 M ⊙ and high molecular gas fractions (f Mol ≡ M Mol/(M * + M Mol) ≈ 0.29–0.87). Their modest star formation rates (SFRs), ≈(0.3–9.5) M ⊙ yr−1, then imply long gas depletion timescales, ≈(3–120) Gyr. The high-metallicity absorption-selected galaxies at z ≈ 0.5–0.8 appear distinct from populations of star-forming galaxies at both z ≈ 1.3–2.5, during the peak of star formation activity in the Universe, and lower redshifts, z ≲ 0.05. Their relatively low SFRs, despite the large molecular gas reservoirs, may indicate a transition in the nature of star formation at intermediate redshifts, z ≈ 0.7.

New research progress of natural gas geological theories in China during the 12th Five-Year Plan period

With the continuous deepening of natural gas exploration, the quality of discovered resources gets worse and exploration targets are getting more and more complicated, so it is necessary to develop and improve natural gas geological theories continuously in order to tap and discover more natural gas resources. Therefore, geological theories on the formation of large gas fields were studied during the 12th Five-Year Plan period and the following progresses were mainly achieved. (1) Gas generation modes were established of oil cracking and highly evolved coal-measure source rocks in different geologic conditions. (2) A model was set up for evaluating quantitatively the hydrocarbon expulsion and detainment of various source rocks with different abundance. (3) Natural gas genesis identification chart was built up with multiple parameters and indexes. (4) Two carbonate rock sedimentation patterns and two tight sandstone sedimentation patterns were established. (5) A new method was developed for evaluating caprock–reservoir displacement pressure difference of immediate caprocks. (6) The hydrocarbon accumulation pattern of large gas fields was established and their main controlling factors and distribution laws were summarized. Then, the natural gas exploration theories were deepened in the following five fields and their application achievements are remarkable. First, the hydrocarbon-accumulation geological theory used for large ancient carbonate gas fields was innovatively understood to promote the discovery and confirmation of the Anyue supergiant gas field in the Sichuan Basin. Second, the hydrocarbon-accumulation geological theory suitable for large tight sandstone gas fields was developed to guide the exploration of tight sandstone gas in the Ordos and Songliao basins. Third, the hydrocarbon-accumulation theory of platform margin reefs was deepened to expand the exploration of platform margin reef gas in the Sichuan Basin. Fourth, the hydrocarbon accumulation mechanism and enrichment theory of large condensate gas reservoirs were deepened to guide the exploration of large condensate gas reservoirs in the Tarim Basin. And fifth, the exploration theory of volcanic gas reservoirs with hydrocarbon-generation fault troughs as basic units was completed to realize the strategic replacement of volcanic gas reservoir exploration.

Rise of the Titans: A Dusty, Hyper-luminous “870 μm Riser” Galaxy at z ∼ 6

Abstract We report the detection of ADFS-27, a dusty, starbursting major merger at a redshift of z = 5.655, using the Atacama Large Millimeter/submillimeter Array (ALMA). ADFS-27 was selected from Herschel/Spectral and Photometric Imaging Receiver (SPIRE) and APEX/LABOCA data as an extremely red “870 μm riser” (i.e., ), demonstrating the utility of this technique to identify some of the highest-redshift dusty galaxies. A scan of the 3 mm atmospheric window with ALMA yields detections of CO(J = 5 → 4) and CO(J = 6 → 5) emission, and a tentative detection of H2O(211 → 202) emission, which provides an unambiguous redshift measurement. The strength of the CO lines implies a large molecular gas reservoir with a mass of M gas = 2.5 × 1011 M ⊙, sufficient to maintain its ∼2400 M ⊙ yr−1 starburst for at least ∼100 Myr. The 870 μm dust continuum emission is resolved into two components, 1.8 and 2.1 kpc in diameter, separated by 9.0 kpc, with comparable dust luminosities, suggesting an ongoing major merger. The infrared luminosity of L IR ≃ 2.4 × 1013 L ⊙ implies that this system represents a binary hyper-luminous infrared galaxy, the most distant of its kind presently known. This also implies star formation rate surface densities of and 750 M ⊙ yr−1 kpc2, consistent with a binary “maximum starburst.” The discovery of this rare system is consistent with a significantly higher space density than previously thought for the most luminous dusty starbursts within the first billion years of cosmic time, easing tensions regarding the space densities of z ∼ 6 quasars and massive quiescent galaxies at z ≳ 3.

ALMA + VLT observations of a damped Lyman-α absorbing galaxy: massive, wide CO emission, gas-rich but with very low SFR

We are undertaking an ALMA survey of molecular gas in galaxies selected for their strong HI absorption, so-called DLA/sub-DLA galaxies. Here we report CO(2-1) detection from a DLA galaxy at z = 0.716. We also present optical and near-infrared spectra of the galaxy revealing [OII], H{\alpha} and [NII] emission lines shifted by ~170 km/s relative to the DLA, and providing an oxygen abundance 3.2 times solar, similar to the absorption metallicity. We report low unobscured SFR ~1 Msun/yr given the large reservoir of molecular gas, and also modest obscured SFR=4.5(+4.4,-2.6) Msun/yr based on far-IR and sub-mm data. We determine mass components of the galaxy: log[M*/Msun] = 10.80(+0.07,-0.14), log[M mol-gas/Msun] = 10.37 +/-0.04, and log[M dust/Msun] = 8.45(+0.10,-0.30). Surprisingly, this HI absorption-selected galaxy has no equivalent objects in CO surveys of flux-selected samples. The galaxy falls off current scaling relations for the SFR to molecular gas mass and CO Tully-Fisher relation. Detailed comparison of kinematical components of the absorbing, ionized and molecular gas, combined with their spatial distribution, suggests that part of the CO gas is both kinematically and spatially de-coupled from the main galaxy. It is thus possible that a major star burst in the past could explain the wide CO profile as well as the low SFR. Support for this also comes from the SED favouring an instantaneous burst of age ~0.5 Gyr. Our survey will establish whether flux-selected surveys of molecular gas are missing a key stage in the evolution of galaxies and their conversion of gas to stars.

Massive Quenched Galaxies at z ∼ 0.7 Retain Large Molecular Gas Reservoirs

Abstract The physical mechanisms that quench star formation, turning blue star-forming galaxies into red quiescent galaxies, remain unclear. In this Letter, we investigate the role of gas supply in suppressing star formation by studying the molecular gas content of post-starburst galaxies. Leveraging the wide area of the Sloan Digital Sky Survey, we identify a sample of massive intermediate-redshift galaxies that have just ended their primary epoch of star formation. We present Atacama Large Millimeter/submillimeter Array CO(2-1) observations of two of these post-starburst galaxies at z ∼ 0.7 with . Their molecular gas reservoirs of and are an order of magnitude larger than comparable-mass galaxies in the local universe. Our observations suggest that quenching does not require the total removal or depletion of molecular gas, as many quenching models suggest. However, further observations are required both to determine if these apparently quiescent objects host highly obscured star formation and to investigate the intrinsic variation in the molecular gas properties of post-starburst galaxies.

Large turbulent reservoirs of cold molecular gas around high-redshift starburst galaxies.

Starburst galaxies at the peak of cosmic star formation are among the most extreme star-forming engines in the Universe, producing stars over about 100 million years (ref. 2). The star-formation rates of these galaxies, which exceed 100 solar masses per year, require large reservoirs of cold molecular gas to be delivered to their cores, despite strong feedback from stars or active galactic nuclei. Consequently, starburst galaxies are ideal for studying the interplay between this feedback and the growth of a galaxy. The methylidyne cation, CH+, is a most useful molecule for such studies because it cannot form in cold gas without suprathermal energy input, so its presence indicates dissipation of mechanical energy or strong ultraviolet irradiation. Here we report the detection of CH+ (J = 1-0) emission and absorption lines in the spectra of six lensed starburst galaxies at redshifts near 2.5. This line has such a high critical density for excitation that it is emitted only in very dense gas, and is absorbed in low-density gas. We find that the CH+ emission lines, which are broader than 1,000 kilometres per second, originate in dense shock waves powered by hot galactic winds. The CH+ absorption lines reveal highly turbulent reservoirs of cool (about 100 kelvin), low-density gas, extending far (more than 10 kiloparsecs) outside the starburst galaxies (which have radii of less than 1 kiloparsec). We show that the galactic winds sustain turbulence in the 10-kiloparsec-scale environments of the galaxies, processing these environments into multiphase, gravitationally bound reservoirs. However, the mass outflow rates are found to be insufficient to balance the star-formation rates. Another mass input is therefore required for these reservoirs, which could be provided by ongoing mergers or cold-stream accretion. Our results suggest that galactic feedback, coupled jointly to turbulence and gravity, extends the starburst phase of a galaxy instead of quenching it.

Detection of a Substantial Molecular Gas Reservoir in a Brightest Cluster Galaxy at z = 1.7

Abstract We report the detection of CO(2–1) emission coincident with the brightest cluster galaxy (BCG) of the high-redshift galaxy cluster SpARCS1049+56, with the Redshift Search Receiver (RSR) on the Large Millimeter Telescope (LMT). We confirm a spectroscopic redshift for the gas of z = 1.7091 ± 0.0004, which is consistent with the systemic redshift of the cluster galaxies of z = 1.709. The line is well fit by a single-component Gaussian with an RSR-resolution-corrected FWHM of 569 ± 63 km s−1. We see no evidence for multiple velocity components in the gas, as might be expected from the multiple image components seen in near-infrared imaging with the Hubble Space Telescope. We measure the integrated flux of the line to be 3.6 ± 0.3 Jy km s−1, and using = 0.8 M ⊙ (K km s−1 pc2)−1, we estimate a total molecular gas mass of 1.1 ± 0.1 × 1011 M ⊙ and a M H2/M ⋆ ∼ 0.4. This is the largest gas reservoir detected in a BCG above z > 1 to date. Given the infrared-estimated star formation rate of 860 ± 130 M ⊙ yr−1, this corresponds to a gas depletion timescale of ∼0.1 Gyr. We discuss several possible mechanisms for depositing such a large gas reservoir to the cluster center—e.g., a cooling flow, a major galaxy–galaxy merger, or the stripping of gas from several galaxies—but conclude that these LMT data are not sufficient to differentiate between them.

A golden era for natural gas development in the Sichuan Basin

Owing to the technical innovation as well as a better understanding of gas exploration, nine giant gas fields have been successively discovered in the Sichuan Basin with cumulative proven gas reserves of 3.69 trillion cubic meters, where the annual natural gas productivity ranks the second in China. The CNPC latest oil & gas resources evaluation results demonstrate that natural gas resources in the Sichuan Basin takes the first place among those petroliferous basins all over China, but its proved gas reserves is only 10%, so the exploration prospect is bright. Over the past decades, PetroChina Southwest Oil & Gas Field Company has made great efforts to complete its technical systems, improve gas pipeline networks, and streamline gas markets, laying a robust foundation for the natural gas development in the Sichuan Basin. To further enhance the natural gas reserves and productivity in this basin and to achieve the biggest gas province in China, this company presents the following major projects: progressive multi-strata exploration and development in the central Sichuan area, Safe and efficient development of high-sulfur gas fields in the northeastern Sichuan area, Demonstrative exploration and development of deep marine carbonate gas reservoirs in the northwestern Sichuan area, Exploitation and development of large Cambrian pre-salt structural gas reservoirs in the eastern Sichuan area, and Extensive and beneficial development of shale gas in southern Sichuan. As the key to the Southwest growth pole, the above projects cover all the important, hard and hot fields of the whole basin and multiple gas-bearing strata and layers. With all the projects fulfilled, natural gas productivity will be 25–29 billion cubic meters (bcm) in 2020, accounting for most parts of this company's whole planning production (30 bcm in total), and will reach up to 50–70 bcm in 2030. It is predicted that natural gas development in the Sichuan Basin will be in a golden era in the long term.