CO Transitions Research Articles

Star-forming brightest cluster galaxies at z ∼ 0.4 in KiDS

Brightest cluster galaxies (BCGs) at the centers of clusters are among the most massive galaxies in the Universe. Their star formation history and stellar mass assembly are highly debated. Recent studies suggest the presence of an emerging population of intermediate-z star-forming and gas-rich BCGs, whose molecular gas reservoirs that feed star formation might be impacted by strong environmental processing. We have selected three of the most strongly star-forming z ∼ 0.4 BCGs in the equatorial field of the Kilo-Degree Survey (KiDS) and observed them with the IRAM 30 m telescope in the first three CO transitions. We found clear double-horn CO(1→0) and CO(3→2) emission for the KiDS 1433 BCG, yielding a large molecular gas reservoir with MH2 = (5.9 ± 1.2)×1010 M⊙ and a high gas-to-stellar mass ratio MH2/M⋆ = (0.32−0.10+0.12). We thus increase the still limited sample of distant BCGs with detections in multiple CO transitions. The double-horn emission for the KiDS 1433 BCG implies a low gas concentration, while a modeling of the spectra yields an extended molecular gas reservoir, with a characteristic radius of ∼(5−7) kpc, which is reminiscent of the mature extended-disk phase that is observed in some local BCGs. For the remaining two BCGs, we are able to set robust upper limits of MH2/M⋆ < 0.07 and < 0.23, which are among the lowest for distant BCGs. We then combined our observations with available stellar, star formation, and dust properties of the targeted BCGs, and compared them with a sample of ∼100 distant cluster galaxies, including additional intermediate-z BCGs, with observations in CO from the literature. Altogether, our analysis shows that the molecular gas properties of star-forming BCGs are heterogeneous. On the one hand, gas-rich BCGs show extended gas reservoirs that sustain the significant star formation activity, but the efficiency is low, which is reminiscent of recent gas infall. On the other hand, the existence of similarly star forming but gas-poor BCGs suggests that gas depletion precedes star formation quenching.

Abundance Ratios of OH/CO and HCO+/CO as Probes of the Cosmic-Ray Ionization Rate in Diffuse Clouds

The cosmic-ray ionization rate (CRIR, ζ 2) is one of the key parameters controlling the formation and destruction of various molecules in molecular clouds. However, the current most commonly used CRIR tracers, such as , OH+, and H2O+, are hard to detect and require the presence of background massive stars for absorption measurements. In this work, we propose an alternative method to infer the CRIR in diffuse clouds using the abundance ratios of OH/CO and HCO+/CO. We have analyzed the response of chemical abundances of CO, OH, and HCO+ on various environmental parameters of the interstellar medium in diffuse clouds and found that their abundances are proportional to ζ 2. Our analytic expressions give an excellent calculation of the abundance of OH for ζ 2 ≤ 10−15 s−1, which are potentially useful for modeling chemistry in hydrodynamical simulations. The abundances of OH and HCO+ were found to monotonically decrease with increasing density, while the CO abundance shows the opposite trend. With high-sensitivity absorption transitions of both CO (1–0) and (2–1) lines from Atacama Large Millimeter/submillimeter Array, we have derived the H2 number densities () toward 4 lines of sight; assuming a kinetic temperature of T k = 50 K, we find a range of (0.14 ± 0.03–1.2 ± 0.1) × 102 cm−3. By comparing the observed and modeled HCO+/CO ratios, we find that ζ 2 in our diffuse gas sample is in the range of × 10 × 10−15 s−1. This is ∼2 times higher than the average value measured at higher extinction, supporting an attenuation of CRs as suggested by theoretical models.

Magnetic transitions in (Co, Fe)-doped ZnO nanoparticles: A Mössbauer and critical exponents study

Zn1-2zFezCozO nanoparticles were synthesized by a lyophilization process followed by thermal annealing. These samples were structurally and magnetically characterized to detail the magnetic ordering at room temperature in magnetic-doped semiconductors. X-ray diffraction results showed that the samples were monophasic for z ≤ 0.03 whereas 57Fe Mössbauer spectroscopy displayed two groups of iron ions substitutional to zinc cations in the wurtzite matrix: isolated iron and iron ions with magnetic neighbors. Magnetic characterization was supported by critical transition analyses and revealed that the samples were paramagnetic at room temperature and transited to a spin-glass-like state at low temperatures after crossing a temperature region with competing ferromagnetic and antiferromagnetic interactions. The study based on critical exponents could be applied successfully for other 3d-doped oxide nanoparticle systems.

Transition metal (X = Mn, Fe, Co, Ni, Cu, Zn)-doped graphene as gas sensor for CO2 and NO2 detection: a molecular modeling framework by DFT perspective.

In this research, CO2 and NO2 adsorption on doped nanographene (NG) sheets with transition metals (Fe, Ni, Zn) and (Mn, Co, Cu), respectively, have been applied for scavenging of these toxic gases as the environmental pollutants. The values of changes of atomic charge density have illustrated a more significant charge transfer for Ni-doped C-NG through CO2 adsorption and a more remarkable charge transfer for Co-doped C-NG through NO2 adsorption. The data of NMR spectroscopy has depicted several fluctuations around the graph of Zn-doped on the nanographene surface. The thermodynamic results from IR spectroscopy have indicated that [Formula: see text] values are almost similar for doped metal transitions of Mn, Co, and Cu on the C-NG nanosheet, while [Formula: see text] has the largest gap of Gibbs free energy adsorption with dipole moment. The Langmuir adsorption model with a three-layered ONIOM using CAM-B3LYP functional accompanying LANL2DZ, EPR-III and 6-31 + G (d,p) basis sets due to Gaussian 16 revision C.01 program on the complexes of CO2 → (Fe, Ni, Zn) and NO2 → (Mn, Co, Cu) doped on the C-NG has been accomplished. Then, NMR and IR spectroscopy, nuclear quadrupole resonance, and natural bond orbital analysis have been accomplished for evaluating chemical shielding tensors, thermodynamic properties, electric potential, and occupancy fluctuation through bond orbitals, respectively. In addition, frontier orbitals of LUMO, HOMO, and also a series of chemical reactivity parameters have been calculated. Finally, time-dependent-DFT method due to UV-VIS spectrums has been accomplished to discern the low-lying excited states of CO2 and NO2 adsorption on the (Fe, Ni, Zn) and (Mn, Co, Cu), respectively, doped C-NG sheet.

Resolved CO(1–0) Emission and Gas Properties in Luminous Dusty Star-forming Galaxies at z = 2–4

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 K km s−1 pc2, and molecular gas masses of 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 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.

Central molecular zones in galaxies: Multitransition survey of dense gas tracers HCN, HNC, and HCO+

New measurements of 46 nearby galaxy centers in up to three transitions of HCN, HNC, and HCO+ combined with literature surveys establish a database of 130 galaxies measured in both HCN and HCO+, and 94 galaxies in HNC as well, allowing a systematic exploration of the relations between normalized luminosities and line ratios. The almost linear relations between luminosities are predominantly caused by distance effects and do not reflect galaxy physical properties. Individual galaxies show significant dispersion in both their luminosity and line ratio, which will be analyzed in more detail in a later paper. Very few line ratios correlate either with luminosities or with other line ratios. Only the normalized transition ladders of HCN and HCO+ and the J = 1 − 0 12CO/13CO isotopologue ratio are positively correlated with CO and far infrared (FIR) luminosity. On average, HCN and HCO+ have very similar intensities and trace the same gas. In galaxies dominated by an active nucleus, HCO+ intensities appear to be depressed relative to HCN intensities. Only a small fraction of CO emission is associated with gas emitting in HCN and HCO+, yet a significant fraction of even that gas appears to be translucent molecular gas. In the observed galaxy centers, the HCN/CO line intensity ratio is not a proxy for the dense gas fraction, and the FIR/HCN and FIR/CO ratios are not proxies for the star formation efficiency. A proper understandig of star formation requires a more appropriate determination of gas mass than provided by the intensities of individual HCN or CO transitions. The observed molecular line emission is fully consistent with UV-photon heating boosted by significant mechanical heating. The molecular gas sampled by HCN and HCO+ has low kinetic temperatures Tkin = 10 − 50 K, low densities nH = 104 − 105 cm−3, and low optical depths in the ground-state lines. Most of the gas sampled by CO has densities lower by one to two orders of magnitude. For a mechanical heating fraction of 0.5, a modest energy input of only G = 300 G0 is required.

A NOEMA Molecular Line Scan of the Hubble Deep Field North: Improved Constraints on the CO Luminosity Functions and Cosmic Density of Molecular Gas

We present measurements of the CO luminosity functions (LFs) and the evolution of the cosmic molecular gas density out to z ∼ 6 based on an 8.5 arcmin2 spectral scan survey at 3 mm of the iconic Hubble Deep Field North (HDF-N) observed with the NOrthern Extended Millimeter Array (NOEMA). We use matched filtering to search for line emission from galaxies and determine their redshift probability distributions exploiting the extensive multiwavelength data for the HDF-N. We identify the seven highest-fidelity sources as CO emitters at 1 < z < 6, including the well-known submillimeter galaxy HDF 850.1 at z = 5.18. Four high-fidelity 3 mm continuum sources are found to be radio galaxies at z ≤ 1, plus HDF 850.1. We constrain the CO LFs in the HDF-N out to z ∼ 6, including a first measurement of the CO(5–4) LF at 〈z〉 = 5.0. The relatively large area and depth of the NOEMA HDF-N survey extends the existing LFs at 1 < z < 4 above the knee, yielding a somewhat lower density by 0.15–0.4 dex at the overlap region for the CO(2–1) and CO(3–2) transitions, attributed to cosmic variance. We perform a joint analysis of the CO LFs in the HDF-N and Hubble Ultra Deep Field from ASPECS, finding that they can be well described by a single Schechter function. The evolution of the cosmic molecular gas density from a joint analysis is in good agreement with earlier determinations. This implies that the impact of cosmic field-to-field variance on the measurements is consistent with previous estimates, adding to the challenges for simulations that model galaxies from first principles.

VLA Legacy Survey of Molecular Gas in Massive Star-forming Galaxies at High Redshift

We present the initial results of an ongoing survey with the Karl G. Jansky Very Large Array targeting the CO(J = 1–0) transition in a sample of 30 submillimeter-selected, dusty star-forming galaxies (SFGs) at z = 2–5 with existing mid-J CO detections from the Atacama Large Millimeter/submillimeter Array and NOrthern Extended Millimeter Array, of which 17 have been fully observed. We detect CO(1–0) emission in 11 targets, along with three tentative (∼1.5σ–2σ) detections; three galaxies are undetected. Our results yield total molecular gas masses of 6–23 × 1010 (α CO/1) M ⊙, with gas mass fractions, f gas = M mol/(M *+M mol), of 0.1–0.8 and a median depletion time of (140 ± 70) Myr. We find median CO excitation ratios of r 31 = 0.75 ± 0.39 and r 41 = 0.63 ± 0.44, with significant scatter. We find no significant correlation between the excitation ratio and a number of key parameters such as redshift, CO(1–0) line width, or ΣSFR. We only find a tentative positive correlation between r 41 and the star-forming efficiency, but we are limited by our small sample size. Finally, we compare our results to predictions from the SHARK semi-analytical model, finding a good agreement between the molecular gas masses, depletion times, and gas fractions of our sources and their SHARK counterparts. Our results highlight the heterogeneous nature of the most massive SFGs at high redshift, and the importance of CO(1–0) observations to robustly constrain their total molecular gas content and interstellar medium properties.

Multiple-color room-temperature phosphorescence regulated by graphitization and carbonyls

Room-temperature phosphorescence with multiple-color activated the widespread interest owing to their promising applications, howbeit, there still exist the insurmountable challenge, especially for elucidating their photoluminescence mechanism and tunable emissions. Here we systematically proposed several carbon dots (CDs) with different degrees of graphitization and amounts of carbonyl while sulfuric acid and ethanol played the critical roles. In brief, sulfuric acid functioned as the carbonization and strong oxidization reagent, while the increasing volumes of ethanol gradually reduced the boiling point of the reactions. Significantly, the energy of these phosphorescent CDs transferred from their excited triplets to oxygen molecules once they were irradiated by UV in aqueous, resulting in the production of the singlet oxygen to oxidize 3,3′,5,5′-tetramethylbenzidine. This finding indirectly provided the evidence for the existence of the phosphorescence rather than delayed fluorescence. Towards the photoluminescence mechanism, their fluorescence of CDs was originated from π-π* transition of CC in the carbon cores and n-π* transition of CO on the surfaces, while RTP was mainly attributed to n-π* transition of the carbonyls. The further evidence suggested that the CDs with different graphitization degrees and amounts of CO regulated their multiple-color phosphorescence. Besides, we employed these CDs for information encryption and preparing LED lamps.

The deconvolved distribution estimator: enhancing reionization-era CO line-intensity mapping analyses with a cross-correlation analogue for one-point statistics

ABSTRACT We present the deconvolved distribution estimator (DDE), an extension of the voxel intensity distribution (VID), in the context of future observations proposed as part of the CO Mapping Array Project (COMAP). The DDE exploits the fact that the observed VID is a convolution of correlated signal intensity distributions and uncorrelated noise or interloper intensity distributions. By deconvolving the individual VID of two observables away from their joint VID in a Fourier-space operation, the DDE suppresses sensitivity to interloper emission while maintaining sensitivity to correlated components. The DDE thus improves upon the VID by reducing the relative influence of uncorrelated noise and interloper biases, which is useful in the context of COMAP observations that observe different rotational transitions of CO from the same comoving volume in different observing frequency bands. Fisher forecasts suggest that the theoretical sensitivity in the DDE allows significant improvements in constraining power compared to either the cross power spectrum or the individual VID data, and matches the constraining power of the combination of all other one- and two-point summary statistics. Future work should further investigate the covariance and model-dependent behaviour of this novel one-point cross-correlation statistic.

Observing circumplanetary disks with METIS

Context. Gaining a full understanding of the planet and moon formation process calls for observations that probe the circumplanetary environment of accreting giant planets. The mid-infrared ELT imager and spectrograph (METIS) will provide a unique capability to detect warm-gas emission lines from circumplanetary disks. Aims. We aim to demonstrate the capability of the METIS instrument on the Extremely Large Telescope (ELT) to detect circumplanetary disks (CPDs) with fundamental v = 1−0 transitions of 12CO from 4.5 to 5 μm. Methods. We considered the case of the well-studied HD 100546 pre-transitional disk to inform our disk modeling approach. We used the radiation-thermochemical disk modeling code ProDiMo to produce synthetic spectral channel maps. The observational simulator SimMETIS was employed to produce realistic data products with the integral field spectroscopic (IFU) mode. Results. The detectability of the CPD depends strongly on the level of external irradiation and the physical extent of the disk, favoring massive (~10 MJ) planets and spatially extended disks, with radii approaching the planetary Hill radius. The majority of 12CO line emission originates from the outer disk surface and, thus, the CO line profiles are centrally peaked. The planetary luminosity does not contribute significantly to exciting disk gas line emission. If CPDs are dust-depleted, the 12CO line emission is enhanced as external radiation can penetrate deeper into the line emitting region. Conclusions. UV-bright star systems with pre-transitional disks are ideal candidates to search for CO-emitting CPDs with ELT/METIS. METIS will be able to detect a variety of circumplanetary disks via their fundamental 12CO ro-vibrational line emission in only 60 s of total detector integration time.

Wastewater-Irrigated Vegetables Are a Significant Source of Heavy Metal Contaminants: Toxicity and Health Risks.

Water contaminated with heavy metals constitutes an important threat. This threat is a real problem with a negative impact in some developing countries where untreated industrial effluents are used for irrigation. The present study examines heavy metals in wastewater-irrigated vegetables (apple gourd, spinach, cauliflower, sponge gourd, and coriander) water, and soil from Chenab Nagar, Chiniot, Pakistan. In particular, the metals quantified were cadmium (Cd), chromium (Cr), cobalt (Co), nickel (Ni), lead (Pb), and manganese (Mn). Among them, Cr and Co in crops irrigated -wastewater exceeded the levels recommended by the World Health Organization (WHO). In contrast, Ni, Cu, Pb, and Mn concentrations were in line with WHO standards. Compared with the limits established by the Food and Agriculture Organization of the United Nations (FAO), all the study vegetables presented higher (thus unsafe) concentrations of Cd (0.38 to 1.205 mg/Kg). There were also unsafe concentrations of Cr in coriander, sponge gourd, and cauliflower. Pb was found at an unsafe concentration (0.59 mg/Kg) in cauliflower. Conversely, Ni and Mn concentrations were below the maximum permissible limits by WHO, and FAO in all of the analyzed samples. The contamination load index (CLI) in soil, bioconcentration factor (BCF) in plants, daily intake of metals (DIM), and health risk index (HRI) have also been evaluated to estimate the potential risk to human health in that area. We have found an important risk of transitions of Pb, Cd, Cr, and Co from water/soil to the edible part of the plant. The highest HRI value associated with Cd (6.10-13.85) followed by Cr (1.25-7.67) for all vegetable samples presented them as high health risk metal contaminants. If the issue is not addressed, consumption of wastewater-irrigated vegetables will continue posing a health risk.

Proposal of spin crossover as a reversible switch of catalytic activity for the oxygen evolution reaction in two dimensional metal-organic frameworks.

The development of oxygen evolution reaction (OER) catalysts with high activity and controllability is crucial for clean energy conversion and storage but remains a challenge. Here, based on first-principles calculations, we propose to utilize spin crossover (SCO) in two-dimensional (2D) metal-organic frameworks (MOFs) to achieve reversible control of OER catalytic activity. The theoretical design of a 2D square lattice MOF with Co as nodes and tetrakis-substituted cyanimino squaric acid (TCSA) as ligands, which transforms between the high spin (HS) and the low spin (LS) state by applying an external strain (∼2%), confirms our proposal. In particular, the HS-LS spin state transition of Co(TCSA) considerably regulates the adsorption strength of the key intermediate HO* in the OER process, resulting in a significant reduction of the overpotential from 0.62 V in the HS state to 0.32 V in the LS state, thus realizing a reversible switch for the activity of the OER. Moreover, the high activity of the LS state is confirmed by microkinetic and constant potential method simulations.

Pure rotational R(0) and R(1) lines of CO in Ar baths: experimental broadening, shifting and mixing parameters in a wide pressure range versus ab initio calculations.

The results of a rigorous study of the two first pure rotational transitions of CO perturbed by Ar are presented. The experimental part is based on the use of three different spectrometers covering together the pressure range from 0.02 up to 1500 torr. The measurement results of collisional line shape parameters are supported by fully ab initio calculations, which are in remarkable agreement with retrieved data. A sub-percent uncertainty of line intensity measurements is achieved and the first firm evidence that the resonance spectrum of CO is observed on the continual pedestal is given. We analyze the results of our ab initio calculations on the basis of early analytical theories and demonstrate a good general applicability of the latter to the CO-Ar collisional system.

Self- and N2- broadening of CO in the low-pressure regime

Sub-Doppler saturated absorption spectroscopy of rovibrational transitions of carbon monoxide broadened by nitrogen was recorded at low pressures (1-24 Pa) near 1.56 µm with comb-locked cavity ring-down saturation spectroscopy. We found a nonlinear pressure dependence of the Lamb-dip width of the CO transition induced by elastic scattering. Analysis of the results allows us to characterize parameters of elastic- and nonelastic- scattering under collisions. The elastic scattering angle for nitrogen-induced collisions (CO-N2) was determined to be larger than 0.6 × 10−3 rad. The line broadening of the Lamb dip in the region of low pressures exceeds the broadening at high pressures by a factor of 4 and 5 for the self- and N2-broadening CO R(9) transition. Moreover, much smaller line shifts for both self- and N2-broaden Lamb dips were observed, which was also attributed to the decrease in the number of scattered molecules in the interaction and the increasing attracting forces.

12CO (3–2) High-Resolution Survey (COHRS) of the Galactic Plane: Complete Data Release

We present the full data release of the 12CO (3–2) High-Resolution Survey (COHRS), which has mapped the inner Galactic plane over the range of 9.°5 ≤ l ≤ 62.°3 and ∣b∣ ≤ 0.°5. COHRS has been carried out using the Heterodyne Array Receiver Program on the 15 m James Clerk Maxwell Telescope in Hawaii. The released data are smoothed to have a spatial resolution of 16.″6 and a velocity resolution of 0.635 km s−1, achieving a mean rms of ∼0.6 K on . The COHRS data are useful for investigating detailed three-dimensional structures of individual molecular clouds and large-scale structures such as spiral arms in the Galactic plane. Furthermore, data from other available public surveys of different CO isotopologues and transitions with similar angular resolutions to this survey, such as FUGIN, SEDIGISM, and CHIMPS/CHIMPS2, allow studies of the physical properties of molecular clouds and comparison of their states. In this paper, we report further observations on the second release and improved data reduction since the original COHRS release. We discuss the characteristics of the COHRS data and present integrated-emission images and a position–velocity (PV) map of the region covered. The PV map shows a good match with spiral-arm traces from existing CO and H i surveys. We also obtain and compare integrated one-dimensional distributions of 12CO (1–0) and (3–2) and those of star-forming populations.

ALMA Observations of the HD 110058 Debris Disk

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the young, gas-rich debris disk around HD 110058 at 0.″3–0.″6 resolution. The disk is detected in the 0.85 and 1.3 mm continuum, as well as the J = 2–1 and J = 3–2 transitions of 12CO and 13CO. The observations resolve the dust and gas distributions and reveal that this is the smallest debris disk around stars of similar luminosity observed by ALMA. The new ALMA data confirm the disk is very close to edge-on, as shown previously in scattered-light images. We use radiative transfer modeling to constrain the physical properties of dust and gas disks. The dust density peaks at around 31 au and has a smooth outer edge that extends out to ∼70 au. Interestingly, the dust emission is marginally resolved along the minor axis, which indicates that it is vertically thick if truly close to edge-on with an aspect ratio between 0.13 and 0.28. We also find that the CO gas distribution is more compact than the dust (similar to the disk around 49 Ceti), which could be due to a low viscosity and a higher gas release rate at small radii. Using simulations of the gas evolution taking into account the CO photodissociation, shielding, and viscous evolution, we find that HD 110058's CO gas mass and distribution are consistent with a secondary origin scenario. Finally, we find that the gas densities may be high enough to cause the outward drift of small dust grains in the disk.

First Detection of the Molecular Cloud Population in the Extended Ultraviolet Disk of M83

We report a CO(J = 3−2) detection of 23 molecular clouds in the extended ultraviolet (XUV) disk of the spiral galaxy M83 with the Atacama Large Millimeter/submillimeter Array. The observed 1 kpc2 region is at about 1.24 times the optical radius (R 25) of the disk, where CO(J = 2–1) was previously not detected. The detection and nondetection, as well as the level of star formation (SF) activity in the region, can be explained consistently if the clouds have the mass distribution common among Galactic clouds, such as Orion A—with star-forming dense clumps embedded in thick layers of bulk molecular gas, but in a low-metallicity regime where their outer layers are CO-deficient and CO-dark. The cloud and clump masses, estimated from CO(3−2), range from 8.2 × 102 to 2.3 × 104 M ⊙ and from 2.7 × 102 to 7.5 × 103 M ⊙, respectively. The most massive clouds appear similar to Orion A in star formation activity as well as in mass, as expected if the cloud mass structure is common. The overall low SF activity in the XUV disk could be due to the relative shortage of gas in the molecular phase. The clouds are distributed like chains up to 600 pc (or longer) in length, suggesting that the trigger of cloud formation is on large scales. The common cloud mass structure also justifies the use of high-J CO transitions to trace the total gas mass of clouds, or galaxies, even in the high-z universe. This study is the first demonstration that CO(3−2) is an efficient tracer of molecular clouds even in low-metallicity environments.

Opportunities beyond CO2 for climate mitigation

Opportunities beyond CO2 for climate mitigation

High-speed mid-infrared laser absorption spectroscopy of CO_2 for shock-induced thermal non-equilibrium studies of planetary entry

A high-speed laser absorption technique is employed to resolve spectral transitions of CO_2 in the mid-infrared at MHz rates to infer non-equilibrium populations/temperatures of translation, rotation and vibration in shock-heated CO_2 - Ar mixtures. An interband cascade laser (DFB-ICL) resolves 4 transitions within the CO_2 asymmetric stretch fundamental bands (Delta v_3 = 1) near 4.19 upmu hbox {m}. The sensor probes a wide range of rotational energies as well as two vibrational states (00^00 and 01^10). The sensor is demonstrated on the UCLA high enthalpy shock tube, targeting temperatures between 1250 and 3100 K and sub-atmospheric pressures (up to 0.2 atm). The sensor is sensitive to multiple temperatures over a wide range of conditions relevant to Mars entry radiation. Vibrational relaxation times are resolved and compared to existing models of thermal non-equilibrium. Select conditions highlight the shortcomings of modeling CO_2 non-equilibrium with a single vibrational temperature.