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Spatial metallicity distribution statistics at ≤100 pc scales in the AMUSING++ nearby galaxy sample
(Oxford University Press, 2023) Li, Zefeng; Wisnioski, Emily; Mendel, Trevor; Krumholz, Mark; Kewley, Lisa; Lopez-Coba,, Carlos; Sanchez, Sebastian F; Anderson, Joseph P; Galbany, L
We analyse the spatial statistics of the 2D gas-phase oxygen abundance distributions in a sample of 219 local galaxies. We introduce a new adaptive binning technique to enhance the signal-to-noise ratio of weak lines, which we use to produce well-filled metallicity maps for these galaxies. We show that the two-point correlation functions computed from the metallicity distributions after removing radial gradients are in most cases well-described by a simple injection-diffusion model. Fitting the data to this model yields the correlation length lcorr, which describes the characteristic interstellar medium (ISM) mixing length-scale. We find typical correlation lengths lcorr ∼1 kpc, with a strong correlation between lcorr and stellar mass, star formation rate (SFR), and effective radius, and a weak correlation with Hubble type. Two galaxies in the sample show significantly larger lcorr, and both prove to be interacting or merging systems. We show that the trend of lcorr with SFR can be reproduced by a simple transport + feedback model of ISM turbulence at high SFR, and plausibly also at low SFR if dwarf galaxy winds have large mass-loading factors. We also report the first measurements of the injection width that describes the initial radii over which supernova remnants deposit metals. Inside this radius the metallicity correlation function is not purely the product of a competition between injection and diffusion. We show that this size scale is generally smaller than 60 pc.
Rotation measure structure functions with higher-order stencils as a probe of small-scale magnetic fluctuations and its application to the Small and Large Magellanic Clouds
(Oxford University Press, 2023) Seta, Amit; Federrath, Christoph; Livingston, Jack; McClure-Griffiths, Naomi
Magnetic fields and turbulence are important components of the interstellar medium (ISM) of star-forming galaxies. It is challenging to measure the properties of the small-scale ISM magnetic fields (magnetic fields at scales smaller than the turbulence driving scale). Using numerical simulations, we demonstrate how the second-order rotation measure (RM, which depends on thermal electron density, ne, and magnetic field, b) structure function can probe the properties of small-scale b. We then apply our results to observations of the Small and Large Magellanic Clouds (SMC and LMC). First, using Gaussian random b, we show that the characteristic scale, where the RM structure function flattens is approximately equal to the correlation length of b. We also show that computing the RM structure function with a higher-order stencil (more than the commonly-used two-point stencil) is necessary to accurately estimate the slope of the structure function. Then, using Gaussian random b and lognormal ne with known power spectra, we derive an empirical relationship between the slope of the power spectrum of b, ne, and RM. We apply these results to the SMC and LMC and estimate the following properties of small-scale b: correlation length (160 ± 21 pc for the SMC and 87 ± 17 pc for the LMC), strength (14 ± 2μG for the SMC and 15 ± 3 μGfor the LMC), and slope of the magnetic power spectrum (−1.3 ± 0.4 for the SMC and −1.6 ± 0.1 for the LMC). We also find that ne is practically constant over the estimated b correlation scales.
[Book Review] The Imperial Discipline: Race and the Founding of International Relations
(Rezensionen, 2023) Akami, Tomoko
Cosmic ray interstellar propagation tool using Itô Calculus (criptic): Software for simultaneous calculation of cosmic ray transport and observational signatures
(Oxford University Press, 2022) Krumholz, Mark; Crocker, Roland; Sampson, Matthew
We present criptic, the Cosmic Ray Interstellar Propagation Tool using Itô Calculus, a new open-source software package to simulate the propagation of cosmic rays through the interstellar medium and to calculate the resulting observable non-thermal emission. criptic solves the Fokker-Planck equation describing transport of cosmic rays on scales larger than that on which their pitch angles become approximately isotropic, and couples this to a rich and accurate treatment of the microphysical processes by which cosmic rays in the energy range ∼MeV to ∼PeV lose energy and produce emission. criptic is deliberately agnostic as to both the cosmic ray transport model and the state of the background plasma through which cosmic rays travel. It can solve problems where cosmic rays stream, diffuse, or perform arbitrary combinations of both, and the coefficients describing these transport processes can be arbitrary functions of the background plasma state, the properties of the cosmic rays themselves, and local integrals of the cosmic ray field itself (e.g. the local cosmic ray pressure or pressure gradient). The code is parallelized using a hybrid OpenMP-MPI paradigm, allowing rapid calculations exploiting multiple cores and nodes on modern supercomputers. Here, we describe the numerical methods used in the code, our treatment of the microphysical processes, and the set of code tests and validations we have performed.
Infrared radiation feedback does not regulate star cluster formation
(Oxford University Press, 2022) Harimohan Menon, Shyam; Federrath, Christoph; Krumholz, Mark
We present 3D radiation-hydrodynamical (RHD) simulations of star cluster formation and evolution in massive, self-gravitating clouds, whose dust columns are optically thick to infrared (IR) photons. We use VETTAM - a recently developed, novel RHD algorithm, which uses the Variable Eddington Tensor closure - to model the IR radiation transport through the cloud. We also use realistic temperature (T) dependent IR opacities (κ) in our simulations, improving upon earlier works in this area, which used either constant IR opacities or simplified power laws (κ α T2). We investigate the impact of the radiation pressure of these IR photons on the star formation efficiency of the cloud, and its potential to drive dusty winds. We find that IR radiation pressure is unable to regulate star formation or prevent accretion on to the star clusters, even for very high gas surface densities (Σ > 105 M⊙ pc-2), contrary to recent semi-analytic predictions and simulation results using simplified treatments of the dust opacity. We find that the commonly adopted simplifications of κ α T2 or constant κ for the IR dust opacities leads to this discrepancy, as those approximations overestimate the radiation force. By contrast, with realistic opacities that take into account the microphysics of the dust, we find that the impact of IR radiation pressure on star formation is very mild, even at significantly high dust-to-gas ratios (∼3 times solar), suggesting that it is unlikely to be an important feedback mechanism in controlling star formation in the ISM.