Search NASA⌕ Search

SEARCH · Search NASA

Results for “ToT”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Techniques for Estimating Emissions Factors from Forest Burning: ARCTAS and SEAC4RS Airborne Measurements Indicate which Fires Produce Ozone

Previous studies of emission factors from biomass burning are prone to large errors since they ignore the interplay of mixing and varying pre-fire background CO2 levels. Such complications severely affected our studies of 446 forest fire plume samples measured in the Western US by the science teams of NASA's SEAC4RS and ARCTAS airborne missions. Consequently we propose a Mixed Effects Regression Emission Technique (MERET) to check techniques like the Normalized Emission Ratio Method (NERM), where use of sequential observations cannot disentangle emissions and mixing. We also evaluate a simpler "consensus" technique. All techniques relate emissions to fuel burned using C(burn) = delta C(tot) added to the fire plume, where C(tot) approximately equals (CO2 = CO). Mixed-effects regression can estimate pre-fire background values of C(tot) (indexed by observation j) simultaneously with emissions factors indexed by individual species i, delta, epsilon lambda tau alpha-x(sub I)/C(sub burn))I,j. MERET and "consensus" require more than emissions indicators. Our studies excluded samples where exogenous CO or CH4 might have been fed into a fire plume, mimicking emission. We sought to let the data on 13 gases and particulate properties suggest clusters of variables and plume types, using non-negative matrix factorization (NMF). While samples were mixtures, the NMF unmixing suggested purer burn types. Particulate properties (b scant, b abs, SSA, AAE) and gas-phase emissions were interrelated. Finally, we sought a simple categorization useful for modeling ozone production in plumes. Two kinds of fires produced high ozone: those with large fuel nitrogen as evidenced by remnant CH3CN in the plumes, and also those from very intense large burns. Fire types with optimal ratios of delta-NOy/delta- HCHO associate with the highest additional ozone per unit Cburn, Perhaps these plumes exhibit limited NOx binding to reactive organics. Perhaps these plumes exhibit limited NOx binding to reactive organics

ozone↗
NASA NTRS2014

True Emission Factors for Forest Fires and the Role of Non-Fire NOx

True Emission Factors for Forest Fires and the Role of Non-Fire NOx Robert B. Chatfield and Meinrat Andreae The standard way to estimate biomass burning emissions factors from airborne, surface, or laboratory data is to relate the emitted pollutant concentration to the carbon burned, C(sub tot), and liberated to the air, mostly CO2. We approximate total emitted carbon C(sub tot) ~ (CO2 + CO). Emission ratios that are based on CO, describing burning effects, delta-parameter delta-CO, are often used to quantify fire emissions. These are not as useful as emission factors, for they often complicate analyses, since delta-CO delta-CO2 may vary by unto tenfold, and can have bias artifacts of similar magnitude. We present a methodology that estimates both emission factors and a reasonable description of background C(sub tot). High O3 values require a history of the balanced interaction of two pollutant types, nitrogen oxides (NOx) and a radical source, VOCs. However, high VOC NOx ratios seen in many plumes, especially from smoldering-dominated fires, make substantial O3 formation less likely. One particularly intense fire we analyzed, the notorious Rim Fire of 2013, near Yosemite, California. It produced notable quantities of free NOx and (both gas- and particle-phase) Cl species. Consequently, we also outline a quantitative way to assess the effects of anthropogenic or lightning NOx. We provide the example of California burning emissions using measurements of HCHO, NO, and the photolysis rate j(sub HCHO).

Chatfield, Robert B.↗
NASA NTRS2019

Emissions Relationships in Western Forest Fire Plumes: I. Reducing the Effect of Mixing Errors on Emission Factors

Studies of emission factors from biomass burning using aircraft data complement the results of lab studies and extend them to conditions of immense hot conflagrations. We illustrate and discuss emission relationships for 422 individual samples from many forest-fire plumes in the Western US. The samples are from two NASA investigations: ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) and SEAC4RS (Studies of Emissions and Atmospheric Composition, Clouds, and Climate Coupling by Regional Surveys). This work provides sample-by-sample enhancement ratios (EnRs) for 23 gases and particulate properties. Many EnRs provide candidates for emission ratios (ERs, corresponding to the EnR at the source) when the origin and degree of transformation is understood and appropriate. From these, emission factors (EFs) can be estimated when the fuel dry mass consumed is known or can be estimated using the carbon mass budget approach. This analysis requires understanding the interplay of mixing of the plume with surrounding air. Some initial examples emphasize that measured C(tot) = CO2 + CO in a fire plume does not necessarily describe the emissions of the total carbon liberated in the flames, C(burn). Rather, it represents C(tot) = C(burn) + C(bkgd), which includes possibly varying background concentrations for entrained air. Consequently, we present a simple theoretical description for plume entrainment for multiple tracers from flame to hundreds of kilometers downwind and illustrate some intrinsic linear behaviors. The analysis suggests a Mixed Effects Regression Emission Technique (MERET), which can eliminate occasional strong biases associated with the commonly used normalized excess mixing ratio (NEMR) method. MERET splits C(tot) to reveal C(burn) by exploiting the fact that C(burn) and all tracers respond linearly to dilution, while each tracer has consistent EnR behavior (slope of tracer concentration with respect to C(burn)). The two effects are separable. Two or three or preferably more emission indicators are required as a minimum; here we used ten. Limited variations in the EnRs for each tracer can be incorporated and the variations and co-variations analyzed. The percentage CO yield (or the modified combustion efficiency) plays some role. Other co-relationships involving nitrogen and organic classes are more prominent; these have strong relationships to the C(burn) to O3 emission relationship. In summary, MERET allows fine spatial resolution (EnRs for individual observations) and comparison of similar plumes distant in time and space. Alkene ratios provide us with an approximate photochemical timescale. This allows discrimination and definition, by fire situation, of ERs, allowing us to estimate emission factors.

Chatfield, Robert B.↗
DOE OSTI2018

First-Principles Investigation of Ferromagnetic, Thermodynamic, Elastic, and Half-Metallic Behavior of ReCrTe and RuCrTe Half-Heusler Alloys

Calculations are realized within the full-potential linearized augmented plane wave (FP-LAPW) computational approach with the generalized gradient approximation (GGA) for the exchange-correlation potential. In this work, we present investigation of structural, electronic, ferromagnetic, elastic, and thermodynamic properties and half-metallic behavior of ReCrTe and RuCrTe compounds. Analysis of band structures and densities of states show the half-metallic ferromagnetic behavior of these compounds. The values of total magnetic moments µ{sub tot} are 1 µ{sub B} per unit cell for ReCrTe and 3 µ{sub B} per unit cell for RuCrTe. The contribution of Cr is the most important. The calculated values of a total magnetic moment nicely follow the rule µ{sub tot} = Z{sub t}− 18. The study of the impacts of strains on the magnetic moment reveals that the two compounds are stable ferromagnetic compounds. RuCrTe compound preserves the half-metallic behavior when the unit cell volume is changed in the range of [ − 4%, 4%], whereas, weak strain destroys the half metallic nature for ReCrTe compound. Using the quasi-harmonic Debye model, the effects of pressure P and temperature T on thermal expansion coefficient, Debye temperature, heat capacity and Grüneisen parameter for these two compounds are investigated for the first time. The study of the elastic constants shows that ReCrTe and RuCrTe are mechanically stable. RuCrTe is stiffer than ReCrTe compounds. The obtained values of Pugh’s ratio B/G and Cauchy pressure (C{sub 12} − C{sub 44}) reveal that ReCrTe and RuCrTe are brittle. The study of the electron charge density and Poisson’s ratio proves that the ionic character dominates the atomic bonding for the two compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Study of Electronic Structure, Magnetism, and Half-Metallicity of New Heusler Compounds CsTmO{sub 2} (Tm = Fe, Co, Ni, and Cu)

The density functional calculations were performed using the full-potential linearized augmented plane wave (FPLAPW) method for new Heusler alloys CsTmO{sub 2} (Tm = Fe, Co, Ni, and Cu). All compounds were stable in FM AlCu{sub 2}Mn-type structure. Results revealed that these alloys can be experimentally synthesized according to the calculated cohesive and formation energies. CsTmO{sub 2} (Tm = Fe, Co, Ni, and Cu) alloys in AlCu{sub 2}Mn-type and CuHg{sub 2}Ti-type structures were half-metallic ferromagnets. The origin of half-metallicity in CsNiO{sub 2} alloy was also discussed. The total magnetic moment of CsTmO{sub 2} (Tm = Fe, Co, Ni, and Cu) alloys in both structures were 3 μ{sub B} per formula unit and obeyed the Slater-Pauling rule (M{sub tot} = 22 − Z{sub tot}). The relationship between the magnetism and half-metallicity of all compounds and the lattice constants was also studied. The half-metallic character in combined alloys CsTmO{sub 2} (Tm = Fe, Co, Ni, and Cu) improved in comparison with Heusler alloys including transition metals which indicated that they may be good candidates for practical applications in spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magneto-electronic and Thermodynamic Properties of Quaternary NiFeMnZ (Z = In, Sn) New Spin Gapless Semiconductors

This paper deals with investigation of magneto-electronic and thermodynamic properties of new spin gapless semiconductor quaternary NiFeMnZ (Z = In, Sn) Heusler alloys. In addition, electronic properties such as band structure and density of states were studied in detail. The obtained results are based on first-principles calculations, using the full potential linearized augmented plane wave (FP-LAPW) method within well-known generalized gradient approximation (GGA) coupling with spin-orbit calculation (SOC) in framework of the density functional theory (DFT) implemented in the WIEN2k package. As results, the alloys were found to be new spin gapless semiconductors (SGSs), and both compounds in LiMgPdSn-type crystal structure are stable. The magnetic moment of NiFeMnIn and NiFeMnSn was 4.39 and 4.99 μ{sub B} per formula unit, respectively. This result is in agreement with the Slater-Pauling rule (M{sub tot} = 24 −Z{sub tot}). Furthermore, the thermodynamic properties were also predicted. All these multifunctionalities lead to crucial interest for developing future spintronics device generations.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Robust Half-Metallicity in Quaternary Heusler Compounds KSrNZ (Z = O, S, and Se)

The first principle calculations based on density functional theory using full potential linearized augmented plane wave method was performed on the quaternary Heusler alloys KSrNZ (Z = O, S, and Se). Studies on structural properties showed that quaternary Heusler alloys KSrNZ (Z = O, S, and Se) were stable in Y{sub I}-type structure. Furthermore, values of formation energies confirmed that these alloys may be synthesized experimentally. Verification of electronic properties resulted that KSrNO, KSrNS, and KSrNSe compounds were half-metals at equilibrium lattice constants with majority band gaps of 4.61, 3.82, and 3.51 eV, respectively. KSrNZ (Z = O, S, and Se) compounds maintained half-metallic behavior in relatively wide ranges of lattice constant under uniform strain distortion. This indicates that these compounds are promising materials for future spintronic applications. Furthermore, the origin of half-metallic characteristic was verified using electronic density of states. Calculations of magnetic properties showed that the total magnetic moments of KSrNZ (Z = O, S, and Se) were obtained equal to 2 μ{sub B} satisfying the famous Slater-Pauling rule (M{sub tot}= 12-Z{sub tot}).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

State-selective and total cross sections for electron capture from the K-shell of multi-electron atoms by fully stripped projectiles

Capture of a K-shell electron by bare fast ions H{sup +}, He{sup 2+} and Li{sup 3+} from multi-electron atomic targets (carbon, nitrogen, oxygen, neon and argon) is theoretically studied by means of the four-body boundary-corrected first Born approximation. In a wide impact energy interval ranging from 100 to 40 000 keV/amu, extensive tables of the obtained state-selective cross sections Q{sub nlm} are presented for each individual final hydrogen-like state described by the usual quantum numbers {n,l,m}. The total cross sections Q{sub nl}, Q{sub n} and Q{sub tot} for capture summed over the quantum numbers m, {l,m} and {n,l,m}, respectively, are also reported. Theoretical cross sections Q{sub tot} are found to compare favorably with the corresponding experimental data. The maximal value of the principal quantum number n has been taken to be n=4, which satisfies the relationship n≥Z{sub P}, where Z{sub P} is the nuclear charge of the projectile. The tabulated state-selective cross sections Q{sub nlm} for single-electron capture by swift nuclei from multi-electron atoms are the first results in the literature on the theory of four-body collisions. The present data for the examined capture processes are of notable interest for many fundamental and applied problems in various interdisciplinary fields ranging from fusion research, plasma physics, astrophysics to radiotherapy.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2018

Exponential number of equilibria and depinning threshold for a directed polymer in a random potential

By extending the Kac–Rice approach to manifolds of finite internal dimension, we show that the mean number ⟨N{sub tot}⟩ of all possible equilibria (i.e. force-free configurations, a.k.a. equilibrium points) of an elastic line (directed polymer), confined in a harmonic well and submitted to a quenched random Gaussian potential in dimension d=1+1, grows exponentially ⟨N{sub tot}⟩ ~exp(r L) with its length L. The growth rate r is found to be directly related to the generalized Lyapunov exponent (GLE) which is a moment-generating function characterizing the large-deviation type fluctuations of the solution to the initial value problem associated with the random Schrödinger operator of the 1D Anderson localization problem. For strong confinement, the rate r is small and given by a non-perturbative (instanton, Lifshitz tail-like) contribution to GLE. For weak confinement, the rate r is found to be proportional to the inverse Larkin length of the pinning theory. As an application, identifying the depinning with a landscape “topology trivialization” phenomenon, we obtain an upper bound for the depinning threshold f{sub c}, in the presence of an applied force, for elastic lines and d-dimensional manifolds, expressed through the mean modulus of the spectral determinant of the Laplace operators with a random potential. We also discuss the question of counting of stable equilibria. Finally, we extend the method to calculate the asymptotic number of equilibria at fixed energy (elastic, potential and total), and obtain the (annealed) distribution of the energy density over these equilibria (i.e. force-free configurations). Some connections with the Larkin model are also established.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2020

Evidence for top quark production in nucleus-nucleus collisions

We report droplets of quark-gluon plasma (QGP), an exotic state of strongly interacting quantum chromodynamics (QCD) matter, are routinely produced in heavy nuclei high-energy collisions. Although the experimental signatures marked a paradigm shift away from expectations of a weakly coupled QGP, a challenge remains as to how the locally deconfined state with a lifetime of a few fm can be resolved. The only colored particle that decays mostly within the QGP is the top quark. Here we demonstrate, for the first time, that top quark decay products are identified, irrespective of whether interacting with the medium (bottom quarks) or not (leptonically decaying W bosons). Using 1.7±0.1 nb -1 of lead-lead (A = 208) collision data recorded by the CMS experiment at a nucleon-nucleon center-of-mass energy of 5.02 TeV, we report evidence of top quark pair ($t\bar{t}$) production. Dilepton final states are selected, and the cross section ($σ_{t\bar{t}}$) is measured from a likelihood fit to a multivariate discriminator using lepton kinematic variables. The $σ_{t\bar{t}}$ measurement is additionally performed considering the jets originating from the hadronization of bottom quarks, which improve the sensitivity to the $t\bar{t}$ signal process. After background subtraction and analysis corrections, the measured $σ_{t\bar{t}}$ is 2.56 ± 0.82(tot) and 2.02 ± 0.69(tot)μb in the two cases, respectively, consistent with predictions from perturbative QCD.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Centrality and pseudorapidity dependence of the charged-particle multiplicity density in Xe–Xe collisions at s NN = 5.44 TeV

In this Letter, the ALICE Collaboration presents the first measurements of the charged-particle multiplicity density, dN ch /dη and total charged-particle multiplicity, N$tot\atop{ch}$, in Xe–Xe collisions at a centre-of-mass energy per nucleon–nucleon pair of $ \sqrt{s_{NN}}$=5.44TeV. The measurements are performed as a function of collision centrality over a wide pseudorapidity range of -3.5<η<5. The values of dN ch /dη at mid-rapidity and N$tot\atop{ch}$ for central collisions, normalised to the number of nucleons participating in the collision (N part ) as a function of $ \sqrt{s_{NN}}$ follow the trends established in previous heavy-ion measurements. The same quantities are also found to increase as a function of Npart, and up to the 5% most central collisions the trends are the same as the ones observed in Pb–Pb at a similar energy. For more central collisions, the Xe–Xe scaled multiplicities exceed those in Pb–Pb for a similar N part . The results are compared to phenomenological models and theoretical calculations based on different mechanisms for particle production in nuclear collisions. All considered models describe the data reasonably well within 15%.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Characterization of the CMS Endcap Timing Layer readout chip prototype with charge injection

We present the characterization of a readout Application-Specific Integrated Circuit (ASIC) for the CMS Endcap Timing Layer (ETL) of the High-Luminosity LHC upgrade with charge injection. The ASIC, named ETROC and developed in a 65 nm CMOS technology, reads out a 16× 16 pixel matrix of the Low-Gain Avalanche Detector (LGAD). The jitter contribution from ETROC is required to be below 40 ps to achieve the 50 ps overall time resolution per hit. The analog readout circuits in ETROC consist of the preamplifier and the discriminator. The preamplifier handles the LGAD charge signal with the most probable value of around 15 fC. The discriminator generates the digital pulse, which provides the Time-Of-Arrival (TOA, leading edge) and Time-Over-Threshold (TOT, pulse width) information. The prototype of ETROC (ETROC0) that implements a single channel of analog readout circuits has been evaluated with charge injection. The jitter of the analog readout circuits, measured from the discriminator's leading edge, is better than 16 ps for a charge larger than 15 fC with the sensor capacitance. The time walk resulting from different pulse heights can be corrected using the TOT measurement. The time resolution distribution has a standard deviation of 29 ps after the time-walk correction from the charge injection. At room temperature, the preamplifier's power consumption is measured to be 0.74 mW and 1.53 mW per pixel in the low- and high-power mode, respectively. Finally, the measured power consumption of the discriminator is 0.84 mW per pixel. With the ASIC alone or the LGAD sensor, The characterization performances fulfill the ETL's challenging requirements.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2024

AstroPix4 — a novel HV-CMOS sensor developed for space based experiments

For the proposed space based gamma-ray observatory All-sky Medium-Energy Gamma-ray Observatory eXplorer (AMEGO-X), a silicon tracker based on a novel High Voltage-CMOS (HV-CMOS) sensor called AstroPix, is currently being developed. Preliminary measurements with the first full reticle prototype AstroPix3 show that the power target of 1.5 mW/cm 2 can currently not be reached due to the digital consumption of 3.08 mW/cm 2 , while the analog power consumption of 1.04 mW/cm 2 and a break down voltage of over 350 V look promising. Based on these results, the design changes in AstroPix4, submitted in May 2023, are presented, containing changes to the time stamp generation and readout architecture. A digital power consumption below 0.25 mW/cm 2 is expected by removing the fast 200 MHz clock used to measure the time-over-threshold (ToT) and an LVDS receiver. A maximum resolution of 3.125 ns for time-of-arrival (ToA) and ToT is reached by adding per-pixel Flash-Time-to-Digital Converter (TDCs) controlled by a global delay-locked loop (DLL).

47 OTHER INSTRUMENTATION↗
DOE OSTI2024

Absorptive corrections to the electromagnetic form factor in high-energy elastic proton-proton scattering

Recently, it was noted that absorptive corrections to the electromagnetic form factor in high-energy proton-proton scattering are important for the theoretical interpretation of the p ↑ p and p ↑ A analyzing power A N ( t ) measurements with the Hydrogen Jet Target polarimeter (HJET) at RHIC. Here, a concise expression for the absorptive correction was derived within the eikonal approach. The resulting analysis reveals a systematic bias, nearly independent of the beam energy, in the experimental determination of the real-to-imaginary ratio ρ when absorption effects are overlooked in the data analysis. Quantification of this bias, as ρ meas = ρ + ( 0.036 ± 0.016 ) bias , was achieved using a Regge fit applied to available proton-proton measurements of ρ meas ( s ) and σ tot meas ( s ) . Considering the potential impact of such an effect on the experimentally determined A N ( t ) , one may enhance consistency between the HJET and STAR measurements of the hadronic spin-flip amplitude. While the sign of the bias in the value of ρ aligns with the anticipated effective increase in the proton charge radius in p p scattering due to absorption, it amplifies the observed discrepancy between σ tot meas and ρ meas values at s = 13 TeV as measured in the TOTEM experiment. Evaluation (using published TOTEM data) of the measured proton-proton d σ / d t dependence on the absorptive corrections indicated that possible soft photon corrections to the hadronic amplitude slope may be essential for such data analysis. Published by the American Physical Society 2024

43 PARTICLE ACCELERATORS↗
DOE OSTI2019

Half-Metallic Characteristic in the New Full–Heusler SrYO{sub 2} (Y = Sc, Ti, V, and Cr)

Half-metallic properties of SrYO{sub 2} (Y = Sc, Ti, V, and Cr) full-Hensler compounds were studied using full-potential linearized augmented plane wave method based on density functional theory. The negative formation energies of SrYO{sub 2} (Y = Sc, Ti, V, and Cr) alloys confirmed that they can be synthesized experimentally. Total energy calculations showed that AlCu{sub 2}Mn-type structure was the ground state structure in all compounds. In both structures, SrYO{sub 2} (Y = Ti, V, and Cr) alloys were half-metallic ferrromagnets, while SrScO{sub 2} was a non- magnetic metal. The origin of half-metallicity was verified for SrCrO{sub 2}. SrYO{sub 2} (Y = Ti, V, and Cr) alloys in both structures were half-metals in a wide range of lattice constants indicating that they are quite robust against hydrostatic strains. The magnetization of SrYO{sub 2} (Y = Ti, V, and Cr) alloys was mainly originated from the 3d electrons of Y (= Ti, V, and Cr) atoms and followed the Slater–Pauling rule: M{sub tot} = Z{sub tot} – 12. Generally, It is expected that SrYO{sub 2} (Y = Ti, V, and Cr) alloys are promising and interesting candidates in the future spintronic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Resolution requirements for energy conservation in kinetic plasma simulations

The kinetic codes used to model the coupled dynamics of electromagnetic fields and charged particle transport have requirements for spatial, temporal, and charge resolution. These requirements may vary by the solution technique and scope of the problem. In this report, we investigate the resolution limits in the energy-conserving implicit particle-in-cell code CHICAGO. This report has the narrow aim of determining the maximum acceptable grid spacing for the dense plasmas generated in models of z-pinch target gases and power-flow electrode plasmas. In the 2D sample problem, the plasma drifts without external forces with velocity of 10 cm/µs. Simulations are scaled by plasma density to maintain uniform strides across the plasma and from the plasma to the boundaries. Additionally, the cloud-in-cell technique is used with 400 particles per cell and Δ t = 0.85× the Courant limit. For the linear cloud distribution, the criterion for conserving energy is Δ E/E tot < 0.01 for 50,000 time steps. The grid resolution is determined to crudely be Δx ≲ 3 l s , where l s is the electron collisionless skin depth. For the second-order cloud distribution the criterion is Δ E/E tot < 0.005 yielding Δx ≤ 15 l s . These scalings are functions of the chosen v d , Δ t , particles-per-cell, and number of steps.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

Resolved Molecular Gas and Star Formation Properties of the Strongly Lensed z = 2.26 Galaxy SDSS J0901+1814

We present ~1'' resolution (~2 kpc in the source plane) observations of the CO (1–0), CO (3–2), Hα, and [N II ] lines in the strongly lensed z = 2.26 star-forming galaxy SDSS J0901+1814. We use these observations to constrain the lensing potential of a foreground group of galaxies, and our source-plane reconstructions indicate that SDSS J0901+1814 is a nearly face-on (i ≈ 30°) massive disk with r 1/2 ≳ 4 kpc for its molecular gas. Using our new magnification factors (μ tot ≈ 30), we find that SDSS J0901+1814 has a star formation rate (SFR) of ${268}_{-61}^{+63}\,{M}_{\odot }\,{\mathrm{yr}}^{-1}$, ${M}_{\mathrm{gas}}=({1.6}_{-0.2}^{+0.3})\times {10}^{11}({\alpha }_{\mathrm{CO}}/4.6)\,{M}_{\odot }$, and ${M}_{\star }=({9.5}_{-2.8}^{+3.8})\times {10}^{10}\,{M}_{\odot }$, which places it on the star-forming galaxy "main sequence." We use our matched high angular resolution gas and SFR tracers (CO and Hα, respectively) to perform a spatially resolved (pixel-by-pixel) analysis of SDSS J0901+1814 in terms of the Schmidt–Kennicutt relation. After correcting for the large fraction of obscured star formation (${\mathrm{SFR}}_{{\rm{H}}\alpha }/{\mathrm{SFR}}_{\mathrm{TIR}}={0.054}_{-0.014}^{+0.015}$), we find that SDSS J0901+1814 is offset from "normal" star-forming galaxies to higher star formation efficiencies independent of assumptions for the CO-to-H 2 conversion factor. Our mean best-fit index for the Schmidt–Kennicutt relation for SDSS J0901+1814, evaluated with different CO lines and smoothing levels, is $\bar{n}=1.54\pm 0.13;$ however, the index may be affected by gravitational lensing, and we find $\bar{n}=1.24\pm 0.02$ when analyzing the source-plane reconstructions. While the Schmidt–Kennicutt index largely appears unaffected by which of the two CO transitions we use to trace the molecular gas, the source-plane reconstructions and dynamical modeling suggest that the CO (1–0) emission is more spatially extended than the CO (3–2) emission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2025

Global Simulations of Gravitational Instability in Protostellar Disks with Full Radiation Transport. I. Stochastic Fragmentation with Optical-depth-dependent Rate and Universal Fragment Mass

Fragmentation in a gravitationally unstable accretion disk can be an important pathway for forming stellar/planetary companions. To characterize quantitatively the condition for and outcome of fragmentation under realistic thermodynamics, we perform global 3D simulations of gravitationally unstable disks at various cooling rates and cooling types, including the first global simulations of gravitational instability that employ full radiation transport. We find that fragmentation is a stochastic process, with the fragment generation rate per disk area p frag showing an exponential dependence on the parameter β ≡ Ω K t cool , where Ω K is the Keplerian rotation frequency, and t cool is the average cooling timescale. Compared to a prescribed constant β, radiative cooling in the optically thin/thick regime makes p frag decrease slower/faster in β; the critical β corresponding to ∼1 fragment per orbit is ≈3, 5, and 2 for constant β, optically thin, and optically thick cooling, respectively. The distribution function of the initial fragment mass is remarkably insensitive to disk thermodynamics. Regardless of cooling rate and optical depth, the typical initial fragment mass is m frag ≈ 40M tot h 3 , with M tot being the total (star+disk) mass and h = H/R being the disk aspect ratio. Applying this result to typical Class 0/I protostellar disks, we find m frag ∼ 20M J , suggesting that fragmentation more likely forms brown dwarfs. Given the finite width of the m frag distribution, forming massive planets is also possible.

gravitational instability↗