Cold Gas Research Articles

MHONGOOSE discovery of a gas-rich low surface brightness galaxy in the Dorado group

We present the discovery of a low-mass, gas-rich low surface brightness galaxy in the Dorado group, at a distance of 17.7 Mpc. Combining deep MeerKAT 21-cm observations from the MeerKAT Observations of Nearby Galactic Objects: Observing Southern Emitters (MHONGOOSE) survey with deep photometric images from the VST Early-type Galaxy Survey (VEGAS) we find a stellar and neutral atomic hydrogen ( gas mass of $M_ and respectively. This low surface brightness galaxy is the lowest-mass detection found in a group beyond the local Universe ($D 10$ Mpc). The dwarf galaxy has the typical overall properties of gas-rich low surface brightness galaxies in the Local group, but with some striking differences. Namely, the MHONGOOSE observations reveal a very low column density ($ disk with asymmetrical morphology possibly supported by rotation and higher velocity dispersion in the centre. There, deep optical photometry and UV observations suggest a recent enhancement of the star formation. Found at galactocentric distances where in the Local Group dwarf galaxies are depleted of cold gas (at a projected distance of $390$ kpc from the group centre), this galaxy is likely on its first orbit within the Dorado group. We discuss the possible environmental effects that may have caused the formation of the disk and the enhancement of star formation (SF), highlighting the short-lived phase (a few hundreds million years) of the gaseous disk, before either SF or hydrodynamical forces will deplete the gas of the galaxy.

The hydrodynamic response of small-scale structure to reionization drives large IGM temperature fluctuations that persist to z = 4

ABSTRACT The thermal history and structure of the intergalactic medium (IGM) at $z \ge 4$ is an important boundary condition for reionization, and a key input for studies using the Ly $\alpha$ forest to constrain the masses of alternative dark matter candidates. Most such inferences rely on simulations that lack the spatial resolution to fully resolve the hydrodynamic response of IGM filaments and minihaloes to H i reionization heating. In this letter, we use high-resolution hydrodynamic + radiative transfer simulations to study how these affect the IGM thermal structure. We find that the adiabatic heating and cooling driven by the expansion of initially cold gas filaments and minihaloes sources significant small-scale temperature fluctuations. These likely persist in much of the IGM until $z \le 4$. Capturing this effect requires resolving the clumping scale of cold, pre-ionized gas, demanding spatial resolutions of ${\le} 2$ $h^{-1}$kpc. Pre-heating of the IGM by X-rays can slightly reduce the effect. Our preliminary estimate of the effect on the Ly $\alpha$ forest finds that, at $\log (k /[{\rm km^{-1} s}]) = -1.0$, the Ly $\alpha$ forest flux power (at fixed mean flux) can increase ${\approx} 10~{{\ \rm per\ cent}}$ going from 8 and 2 $h^{-1}$kpc resolution at $z = 4{\!-\!}5$ for gas ionized at $z \ \lt\ 7$. These findings motivate more careful analyses of how the effects studied here affect the Ly $\alpha$ forest.

Multi-Cohort Transcriptomic Profiling of Medical Gas Plasma-Treated Cancers Reveals the Role of Immunogenic Cell Death.

The therapeutic potential of cold physical gas plasma operated at atmospheric pressure in oncology has been thoroughly demonstrated in numerous preclinical studies. The cytotoxic effect on malignant cells has been attributed mainly to biologically active plasma-generated compounds, namely, reactive oxygen and nitrogen species. The intracellular accumulation of reactive oxygen and nitrogen species interferes strongly with the antioxidant defense system of malignant cells, activating multiple signaling cascades and inevitably leading to oxidative stress-induced cell death. This study aims to determine whether plasma-induced cancer cell death operates through a universal molecular mechanism that is independent of the cancer cell type. Using whole transcriptome data, we sought to investigate the activation mechanism of plasma-treated samples in patient-derived prostate cell cultures, melanoma, breast, lymphoma, and lung cancer cells. The results from the standardized single-cohort gene expression analysis and parallel multi-cohort meta-analysis strongly indicate that plasma treatment globally induces cancer cell death through immune-mediated mechanisms, such as interleukin signaling, Toll-like receptor cascades, and MyD88 activation leading to pro-inflammatory cytokine release and tumor antigen presentation.

WISDOM project XX. – Strong shear tearing molecular clouds apart in NGC 524

ABSTRACT Early-type galaxies (ETGs) are known to harbour dense spheroids of stars but scarce star formation (SF). Approximately a quarter of these galaxies have rich molecular gas reservoirs yet do not form stars efficiently. We study here the ETG NGC 524, with strong shear suspected to result in a smooth molecular gas disc and low star-formation efficiency (SFE). We present new spatially resolved observations of the 12CO(2-1)-emitting cold molecular gas from the Atacama Large Millimeter/sub-millimeter Array (ALMA) and of the warm ionized-gas emission lines from SITELLE at the Canada–France–Hawaii Telescope. Although constrained by the resolution of the ALMA observations (≈37 pc), we identify only 52 GMCs with radii ranging from 30 to 140 pc, a low mean molecular gas mass surface density 〈Σgas〉 ≈ 125 M⊙ pc−2 and a high mean virial parameter 〈αobs, vir〉 ≈ 5.3. We measure spatially resolved molecular gas depletion times (τdep ≡ 1/SFE) with a spatial resolution of ≈100 pc within a galactocentric distance of 1.5 kpc. The global depletion time is ≈2.0 Gyr but τdep increases towards the galaxy centre, with a maximum τdep, max ≈ 5.2 Gyr. However, no pure H ii region is identified in NGC 524 using ionized-gas emission-line ratio diagnostics, so the τdep inferred are in fact lower limits. Measuring the GMC properties and dynamical states, we conclude that shear is the dominant mechanism shaping the molecular gas properties and regulating SF in NGC 524. This is supported by analogous analyses of the GMCs in a simulated ETG similar to NGC 524.

Micronewton Cold Gas Thruster Based on Silicon-Etched Two-Dimensional Nozzles

The micronewton thruster is one of the essential technologies for providing an ultrastable satellite platform for scientific experiments in space. Particularly, space gravitational wave detection requires a microthruster with continuously adjustable thrust, high resolution, low noise, and fast response. To meet these requirements, we designed a two-dimensional (2D) nozzle and manufactured it using micro-electro-mechanical systems (MEMS). Compared to the nozzles machined with conventional methods, the nozzles etched by the MEMS can easily reach a micron size and form arrays to create mutual backups and also provide a way to widen the thrust range by switching the number of openings. Based on a single 2D nozzle, a cold gas microthruster prototype is constructed with nitrogen gas as the propellant. The thrust of the prototype is tested by a pendulum, the range can span 0–156 μN, the thrust resolution is better than 0.1 μN, and the thrust noise reaches 0.1 μN/Hz1/2 at 0.1 Hz. The result demonstrates that the scheme has the potential to be applied to gravitational wave detection missions.

Internal 1000 au Scale Structures of the R CrA Cluster-forming Cloud. I. Filamentary Structures

We report Atacama Large Millimeter/submillimeter Array/Atacama Compact Array observations of a high-density region of the Corona Australis cloud forming a young star cluster, and the results of resolving internal structures. In addition to embedded Class 0/I protostars in the continuum, a number of complex dense filamentary structures are detected in the C18O and SO lines by the 7 m array. These are substructures of the molecular clump that are detected by the total power array as extended emission. We identify 101 and 37 filamentary structures with widths of a few thousand astronomical units in C18O and SO, respectively, which are called feathers. The typical column density of the feathers in C18O is about 1022 cm−2, and the volume density and line mass are ∼105 cm−3 and a few M ☉ pc−1, respectively. This line mass is significantly smaller than the critical line mass expected for cold and dense gas. These structures have complex velocity fields, indicating a turbulent interior. The number of feathers associated with Class 0/I protostars is only ∼10, indicating that most of them do not form stars but rather are transient structures. The formation of feathers can be interpreted as a result of colliding gas flow because the morphology is well reproduced by MHD simulations, and this is supported by the presence of H i shells in the vicinity. The colliding gas flows may accumulate gas and form filaments and feathers, and trigger the active star formation of the R CrA cluster.

PHANGS-ML: Dissecting Multiphase Gas and Dust in Nearby Galaxies Using Machine Learning

The PHANGS survey uses Atacama Large Millimeter/submillimeter Array, Hubble Space Telescope, Very Large Telescope, and JWST to obtain an unprecedented high-resolution view of nearby galaxies, covering millions of spatially independent regions. The high dimensionality of such a diverse multiwavelength data set makes it challenging to identify new trends, particularly when they connect observables from different wavelengths. Here, we use unsupervised machine-learning algorithms to mine this information-rich data set to identify novel patterns. We focus on three of the PHANGS-JWST galaxies, for which we extract properties pertaining to their stellar populations; warm ionized and cold molecular gas; and polycyclic aromatic hydrocarbons (PAHs), as measured over 150 pc scale regions. We show that we can divide the regions into groups with distinct multiphase gas and PAH properties. In the process, we identify previously unknown galaxy-wide correlations between PAH band and optical line ratios and use our identified groups to interpret them. The correlations we measure can be naturally explained in a scenario where the PAHs and the ionized gas are exposed to different parts of the same radiation field that varies spatially across the galaxies. This scenario has several implications for nearby galaxies: (i) The uniform PAH ionized fraction on 150 pc scales suggests significant self-regulation in the interstellar medium, (ii) the PAH 11.3/7.7 μm band ratio may be used to constrain the shape of the non-ionizing far-ultraviolet to optical part of the radiation field, and (iii) the varying radiation field affects line ratios that are commonly used as PAH size diagnostics. Neglecting this effect leads to incorrect or biased PAH sizes.

The effects of environment on galaxies’ dynamical structures: From simulations to observations

We studied the effects of cluster environments on galactic structures by using the TNG50 cosmological simulation and observed galaxies in the Fornax cluster. We focused on galaxies with stellar masses of 108 − 12 M⊙ at z = 0 that reside in Fornax-like clusters with total masses of M200c = 1013.4 − 14.3 M⊙. We characterized the stellar structures by decomposing each galaxy into a dynamically cold disk and a hot non-disk component, and studied the evolution of both the stellar and gaseous constituents. In TNG50, we find that the cold (i.e., star-forming) gas is quickly removed when a galaxy falls into a Fornax-mass cluster. About 42%, 73%, and 87% of the galaxies have lost 80% of their star-forming gas at 1, 2, and 4 billion years after infall, respectively, with the remaining gas concentrating in the inner regions of the galaxy. The radius of the star-forming gaseous disk decreases to half its original size at 1, 2, and 4 billion years after infall for 7%, 27%, and 66% of the galaxies, respectively. As a result, star formation (SF) in the extended dynamically cold disk sharply decreases, even though a low level of SF persists at the center for a few additional gigayears. This leads to a tight correlation between the average stellar age in the dynamically cold disk and the infall time of galaxies. Furthermore, the luminosity fraction of the dynamically cold disk in ancient infallers (i.e., with an infall time ≳8 Gyr ago) is only about one-third of that in recent infallers (infall time ≲4 Gyr ago), controlling for galaxy stellar mass. This quantitatively agrees with what is observed in early-type galaxies in the Fornax cluster. Gas removal stops the possible growth of the disk, with gas removed earlier in galaxies that fell in earlier, and hence the cold-disk fraction is correlated with the infall time. The stellar disk can be significantly disrupted by tidal forces after infall, through a long-term process that enhances the difference among cluster galaxies with different infall times.

Star formation across cosmic time

The interstellar medium of galaxies is composed of multiple phases, including molecular, atomic, and ionized gas, as well as dust. Stars are formed within this medium from cold molecular gas clouds, which collapse due to their gravitational attraction. Throughout their life, stars emit strong radiation fields and stellar winds, and they can also explode as supernovae at the end of their life. These processes contribute to stirring the turbulent interstellar medium and regulate star formation by heating up, ionizing, and expelling part of the gas. However, star formation does not proceed uniformly throughout the history of the Universe and decrease by an order of magnitude in the last ten billion years. To understand this winding-down of star formation and assess possible variations in the efficiency of star formation, it is crucial to probe the molecular gas reservoirs from which stars are formed. In this article following my presentation at the 10th International Conference on Frontiers of Plasma Physics and Technology held in Kathmandu from 13–17 March 2023, I review some aspects of the multiphase interstellar medium and star formation, with an emphasis on the interplay between neutral and ionized phases, and present recent and ongoing observations of the molecular gas content in typical star-forming galaxies across cosmic time and in different environments. I also present some of our understanding of star-forming galaxies from theoretical models and simulations.

Influence of Different Copper Feedstock Powders on the Microstructure and Corrosion Resistance of Coatings Prepared by Cold Gas Spray

Influence of Different Copper Feedstock Powders on the Microstructure and Corrosion Resistance of Coatings Prepared by Cold Gas Spray

Investigation of the Compound Strength of Hybrid Casting Components with Different Variations of Coated and Undercut Sheet Metal

AbstractLightweight design can reduce CO2 emissions and improve energy efficiency, especially in the fuel-intensive transportation sector. Multi-material design approaches can combine specific properties of materials for effective lightweight design. A multi-material component made from two metals used widely in industry could combine the exceptionally lightweight properties of aluminum with the strength and structural integrity of steel. However, joining aluminum and steel is a challenge due to their different thermo-physical properties and the possible formation of brittle intermetallic phases. In hybrid casting, aluminum is cast around a steel sheet insert in a high-pressure die casting process to produce complex parts. In a first approach, a cold gas sprayed aluminum coating on the insert was tested as a bonding agent between the steel substrate and the molten aluminum. The joint was achieved by a combination of metallurgical bonding and micro-clamping. As a second option, surface structures with undercuts were applied to the steel sheet by modified cold rolling, which allowed the molten aluminum to flow into the channels and interlock with the solid steel. Different orientations of the structure on the insert were tested. In addition, the combination of both approaches was used to potentially enhance the positive effect of the pretreatment techniques. Given the critical importance of joint strength, the quality of these approaches was tested by static tensile tests and dynamic fatigue tests. The results show that the joint by coatings is strongly influenced by the process temperature. The improvement of the joint by the surface structure depends on its orientation to the melt flow.

An artificial intelligence study on energy, exergy, and environmental aspects of upcycling face mask waste to a hydrogen-rich syngas through a thermal conversion process

Studies in the field of gasification process for face mask wastes play a significant role in addressing the environmental issues associated with these wastes and harnessing their potential as an important energy source. On the other hand, machine learning techniques offer a promising approach to predict the environmental, energy, and exergy performances of the gasification process. This study addressed the utilization of machine learning techniques on the gasification process of face mask wastes. Various polynomial regression machine learning algorithms are developed for syngas lower heating value, exergy and cold gas efficiencies, and emission level and their performances are checked. Remarkable precision of machine learning algorithms in forecasting the response variables is evidenced by the impressive outcomes. In fact, the majority of cases yield R-sq values surpassing 98%, thus highlighting their effectiveness. Specifically, when it comes to exergy and cold gas efficiencies, and emission, the machine learning algorithms achieve exceptional R-sq values of 99.85%, 98.93%, and 99.33%, respectively. These exceptional results confirm the credibility and accuracy of these algorithms in providing precise predictions. Leveraging the power of artificial intelligence not only contributes to the development of more sustainable energy systems but also helps in making informed decisions regarding process design and operation.

H i discs of L* galaxies as probes of the baryonic physics of galaxy evolution

ABSTRACT Understanding what shapes the cold gas component of galaxies, which both provides the fuel for star formation and is strongly affected by the subsequent stellar feedback, is a crucial step towards a better understanding of galaxy evolution. Here, we analyse the H i properties of a sample of 46 Milky Way halo-mass galaxies, drawn from cosmological simulations (EMP-Pathfinder and Firebox). This set of simulations comprises galaxies evolved self-consistently across cosmic time with different baryonic sub-grid physics: three different star formation models [constant star formation efficiency (SFE) with different star formation eligibility criteria, and an environmentally dependent, turbulence-based SFE] and two different feedback prescriptions, where only one sub-sample includes early stellar feedback. We use these simulations to assess the impact of different baryonic physics on the H i content of galaxies. We find that the galaxy-wide H i properties agree with each other and with observations. However, differences appear for small-scale properties. The thin H i discs observed in the local universe are only reproduced with a turbulence-dependent SFE and/or early stellar feedback. Furthermore, we find that the morphology of H i discs is particularly sensitive to the different physics models: galaxies simulated with a turbulence-based SFE have discs that are smoother and more rotationally symmetric, compared to those simulated with a constant SFE; galaxies simulated with early stellar feedback have more regular discs than supernova-feedback-only galaxies. We find that the rotational asymmetry of the H i discs depends most strongly on the underlying physics model, making this a promising observable for understanding the physics responsible for shaping the interstellar medium of galaxies.

Enabling plastic waste gasification by autothermal chemical looping with > 90 % syngas purity for versatile feedstock handling

The chemical looping gasification of plastics (CLGP) is a process that offers an innovative solution for transforming post-consumer waste plastics into high-value products. The process utilizes a co-current moving bed reducer reactor with iron-titanium-based oxygen carriers to gasify plastic feed and generate syngas autothermally. Its distinguishing feature is its ability to operate over a wide range of feed loadings and co-injection of mixed plastic species without any performance losses. Isothermal bench-scale experiments reveal a syngas purity of ∼95 %, aligning with the thermodynamic simulations. The moving bed reactor facilitates a deeper reduction of the oxygen carriers to the Fe+FeTiO3 phase, leading to the high syngas purity, which is then verified with additional TGA, XRD, and SEM analysis. For an autothermal operation of CLGP process, an active material content of 20 % is found to be sufficient to satisfy the kinetic and thermodynamic constraints. Further integration with downstream production of H2 is presented and compared to a steam gasification process. The process integration simulations show that the CLGP process outperforms the steam gasification system in terms of Cold Gas Efficiency (CGE), Effective Thermal Efficiency (ETE), and H2 yield. CO2 emissions are impressively reduced by ∼30 % in the CLGP system over that in the steam gasification system due to its ability to autothermally operate the process, unlike the highly endothermic steam gasification process.

Cooperative effects in dense cold atomic gases including magnetic dipole interactions

We theoretically investigate cooperative effects in cold atomic gases exhibiting both electric and magnetic dipole-dipole interactions, such as occurs, for example, in clouds of dysprosium atoms. After introducing a general framework capturing both the quantum degenerate and nondenegerate cases, we focus on the emergence of tailorable spin models in the quantum nondegenerate regime. In the low-excitation limit, we provide analytical and numerical results detailing the effect of magnetic interactions on the directionality of scattered light and characterize sub and superradiant effects. Published by the American Physical Society 2024

Consequences of a low-mass high-pressure star formation mode in early galaxies

ABSTRACT High resolution X-ray spectra reveal hidden cooling flows depositing cold gas at the centres of massive nearby early-type galaxies with little sign of normal star formation. Optical observations are revealing that a bottom-heavy initial mass function is common within the inner kpc of similar galaxies. We revive the possibility that a low-mass star formation mode is operating due to the high thermal pressure in the cooling flow, thus explaining the accumulation of low-mass stars. We further explore whether such a mode operated in early high-redshift galaxies and has sporadically continued to the present day. The idea links observed distant galaxies with black holes which are ultramassive for their stellar mass, nearby red nuggets and massive early-type galaxies. Nearby elliptical galaxies may be red but they are not dead.

Experimental assessment of oxy-CO2 gasification strategy with woody biomass

This paper presents the results obtained during an extensive experimental campaign focused on analysing the application of Oxy-CO2 gasification technology to a small downdraft gasifier fed with woody biomass. Oxy-gasification enables the production of a nitrogen-free synthesis gas (syngas), which can be effectively employed in the synthesis of various high-value chemicals, including but not limited to synthetic natural gas (SNG), methanol (CH3OH), ammonia (NH3), hydrogen and more.The gasifier performances were analysed using different CO2/O2 ratios in the feed (between 1 and 3 kg/kg). The inlet biomass flow rate was approximately 12–18 kg/h, while the equivalence ratio ranged between 19 % and 26 %. The results show that the gasifier can produce a syngas flow rate in the range of 15–25 Nm3/h with a lower heating value (LHV) of between 8 and 10 MJ/Nm3 and a cold gas efficiency of up to 78 %. The operative behaviour of the gasification system is stable and simple to control.

Computational study of a helium-propellant microwave electrothermal thruster

The microwave electrothermal thruster (MET) utilizes wave-exited microdischarges to heat gas flows, enhancing the specific impulse of the thruster. Our computational study investigates a 17.5 GHz helium-propellant MET, employing a two-dimensional, axisymmetric fluid model of plasma coupled with electromagnetic wave and gas flows. The discharges operate in the glow regime, remaining weakly ionized, and in thermal non-equilibrium. The plasma densities reach approximately 1020m−3, and the gas temperature is around 2000 K. Even a slight off-resonant frequency operation results in a significantly lower plasma density and gas temperature. Gas heating, primarily driven by electromagnetic Joule heating, plays a critical role in influencing the overall discharge behavior. The measured peak thrust and specific impulse are 8.24 mN and 292 s, respectively, at a mass flow rate of 3.2 mg/s with 30 W of power. Compared to a cold gas thruster, there is a significant increase in the specific impulse by a factor of approximately 1.7. The enhanced performance trades off with propulsive efficiency, which decreases by a factor of 1.5 from the peak 65% at 10 W. This is due to higher energy losses to cavity walls from heat conduction with increased power. These findings underscore the critical balance between the input power and mass flow rate to improve the MET performance, highlighting the importance of power management to maximize thrust and efficiency. Furthermore, the predicted thrust and specific impulse agree well with experimental values for nominally similar MET thruster studies in the literature.

Temperature stratification in a molecular shock: Analysis of the emission of H2 pure rotational lines in IC443G

Context. Supernovae remnants (SNRs) represent a major source of feedback from stars on the interstellar medium of galaxies. During the latest stage of supernova explosions (which lasts 10–100 kyr), shock waves produced by the initial blast modify the chemistry of gas and dust, inject kinetic energy in the surroundings, and may alter star formation characteristics. Simultaneously, γ-ray emission is generated by the interaction between the ambient medium and cosmic rays, in particular those locally accelerated in the early stages of the explosion. Aims. We aim to estimate the total molecular mass, local density, and total column density of H2 and the temperature structure in a shocked clump interacting with the supernova remnant IC443 located in a region where cosmic rays interact with the interstellar medium. Measuring the mass of the dense and neutral component of the medium is a prerequisite to understanding the chemistry, energetics, and GeV to TeV γ-ray emission. Methods. Assuming that the emission of H2 pure rotational lines is produced by a collection of gas layers with variable temperature, we compared Spitzer/IRS emission maps for the ν = 0–0 S(0) to S(7) lines with a thermal admixture model. Our description is based on a power-law distribution of thermalized components with temperatures varying between Tmin = 25 K and Tmax = 1500 K. Results. Our thermal admixture model allows the level populations of H2 to be described by a power-law distribution dN = ΛT−ΓdT, with Γ ~ 2.2−4.7. We measured a total mass MH2 = 220−80+110 M⊙ across the Spitzer/IRS field of observations. Conclusions. Our analysis shows that an estimate of the cold molecular gas temperature is paramount to accurately constraining the H2 mass, although the mass remains affected by significant uncertainties due to the assumptions on the gas temperature distribution.

Development of Brayton circulating cooling system

The Brayton Circulating Cooling System is a unique refrigeration system designed to demonstrate the basic technology needed to provide cold helium gas refrigeration at high pressures to an external superconducting magnet or any remote load for cool down purposes. The system is designed to provide cool down refrigeration from room temperature to target minimum temperatures of approximately 40 K. The system consists of an F-70H helium compressor with gas control manifold, interconnecting gas lines, cables, the Brayton refrigeration unit mounted in a Dewar assembly and control system. The helium compressor uses high purity helium gas for its refrigerant. Electricity, cooling water for the compressor and a source of pure helium (99.995%) for make-up gas are the only required utilities. The scope of the project, system design, target specifications and summary of test results will be discussed in this paper.