Comparing simulated 26Al maps to gamma-ray measurements

Context. The diffuse gamma-ray emission of 26Al at 1.8 MeV reflects ongoing nucleosynthesis in the Milky Way and traces massive-star feedback in the interstellar medium due to its 1 Myr radioactive lifetime. The morphology and dynamics of the interstellar medium are investigated in astrophysics through 3D hydrodynamic simulations in fine detail as there are few suitable astronomical probes available. Aims. We aim to compare a galactic-scale hydrodynamic simulation of the Galaxy’s interstellar medium, including feedback and nucleosynthesis, with gamma-ray data on 26Al emission in the Milky Way, extracting constraints that are only weakly dependent on the particular realisation of the simulation or Galaxy structure. Methods. Due to constraints and biases in both the simulations and the gamma-ray observations, such comparisons are not straightforward. For a direct comparison, we performed maximum likelihood fits of both simulated sky maps and observation-based maximum entropy maps to measurements using INTEGRAL/SPI. In order to study general morphological properties, we compare the scale heights of 26Al emission produced by the simulation to INTEGRAL/SPI measurements. Results. The direct comparison shows that the simulation describes the observed inner Galaxy well, however it differs significantly from the observed full-sky emission morphology. Comparing the scale height distribution, we see similarities for small-scale height features and a mismatch at larger-scale heights. We attribute this to prominent foreground emission sites which are not captured by the simulation.

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The effects of cosmic rays on the formation of Milky Way-mass galaxies in a cosmological context

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1960 ◽

2020 ◽

Vol 497 (2) ◽

pp. 1712-1737 ◽

Cited By ~ 3

Author(s):

Tobias Buck ◽

Christoph Pfrommer ◽

Rüdiger Pakmor ◽

Robert J J Grand ◽

Volker Springel

Keyword(s):

Cosmic Rays ◽

Milky Way ◽

Gamma Ray ◽

Transport Model ◽

Formation Rate ◽

Wave Model ◽

Alfven Wave ◽

Small Scale ◽

Density Peaks ◽

The Impact

ABSTRACT We investigate the impact of cosmic rays (CRs) and different modes of CR transport on the properties of Milky Way-mass galaxies in cosmological magnetohydrodynamical simulations in the context of the AURIGA project. We systematically study how advection, anisotropic diffusion, and additional Alfvén-wave cooling affect the galactic disc and the circumgalactic medium (CGM). Global properties such as stellar mass and star formation rate vary little between simulations with and without various CR transport physics, whereas structural properties such as disc sizes, CGM densities, or temperatures can be strongly affected. In our simulations, CRs affect the accretion of gas on to galaxies by modifying the CGM flow structure. This alters the angular momentum distribution that manifests itself as a difference in stellar and gaseous disc size. The strength of this effect depends on the CR transport model: CR advection results in the most compact discs while the Alfvén-wave model resembles more the AURIGA model. The advection and diffusion models exhibit large (r ∼ 50 kpc) CR pressure-dominated gas haloes causing a smoother and partly cooler CGM. The additional CR pressure smoothes small-scale density peaks and compensates for the missing thermal pressure support at lower CGM temperatures. In contrast, the Alfvén-wave model is only CR pressure dominated at the disc–halo interface and only in this model the gamma-ray emission from hadronic interactions agrees with observations. In contrast to previous findings, we conclude that details of CR transport are critical for accurately predicting the impact of CR feedback on galaxy formation.

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Dynamic roughness model for large-eddy simulation of turbulent flow over multiscale, fractal-like rough surfaces

Journal of Fluid Mechanics ◽

10.1017/jfm.2011.137 ◽

2011 ◽

Vol 679 ◽

pp. 288-314 ◽

Cited By ~ 67

Author(s):

W. ANDERSON ◽

C. MENEVEAU

Keyword(s):

Large Eddy Simulation ◽

Turbulent Flow ◽

Power Law ◽

Rough Surfaces ◽

Scale Height ◽

Small Scale ◽

Height Distribution ◽

Subgrid Scale ◽

Eddy Simulation ◽

Large Eddy

Many flows especially in geophysics involve turbulent boundary layers forming over rough surfaces with multiscale height distribution. Such surfaces pose special challenges for large-eddy simulation (LES) when the filter scale is such that only part of the roughness elements of the surface can be resolved. Here we consider LES of flows over rough surfaces with power-law height spectra Eh(k) ~ kβs (−3 ≤ βs < −1), as often encountered in natural terrains. The surface is decomposed into resolved and subgrid-scale height contributions. The effects of the unresolved small-scale height fluctuations are modelled using a local equilibrium wall model (log-law or Monin–Obukhov similarity), but the required hydrodynamic roughness length must be specified. It is expressed as the product of the subgrid-scale root-mean-square of the height distribution and an unknown dimensionless quantity, α, the roughness parameter. Instead of specifying this parameter in an ad hoc empirical fashion, a dynamic methodology is proposed based on test-filtering the surface forces and requiring that the total drag force be independent of filter scale or resolution. This dynamic surface roughness (DSR) model is inspired by the Germano identity traditionally used to determine model parameters for closing subgrid-scale stresses in the bulk of a turbulent flow. A series of LES of fully developed flow over rough surfaces are performed, with surfaces built using random-phase Fourier modes with prescribed power-law spectra. Results show that the DSR model yields well-defined, rapidly converging, values of α. Effects of spatial resolution and spectral slopes are investigated. The accuracy of the DSR model is tested by showing that predicted mean velocity profiles are approximately independent of resolution for the dynamically computed values of α, whereas resolution-dependent results are obtained when using other, incorrect, α values. Also, strong dependence of α on βs is found, where α ranges from α ~ 0.1 for βs = −1.2 to α ~ 10−5 for βs = −3.

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The Surroundings of Gamma-Ray Bursts: Constraints on Progenitors

International Astronomical Union Colloquium ◽

10.1017/s0252921100009520 ◽

2005 ◽

Vol 192 ◽

pp. 441-450

Author(s):

Roger A. Chevalier

Keyword(s):

Interstellar Medium ◽

Mass Loss ◽

Massive Star ◽

Gamma Ray ◽

Gamma Ray Bursts ◽

Uniform Density ◽

Stellar Winds ◽

Wind Environment ◽

Low Mass ◽

Pulsar Wind

SummaryThe association of a supernova with a gamma-ray burst (GRB 030329) implies a massive star progenitor, which is expected to have an environment formed by pre-burst stellar winds. Although some sources are consistent with the expected wind environment, many are not, being better fit by a uniform density environment. One possibility is that this is a shocked wind, close to the burst because of a high interstellar pressure and a low mass loss density. Alternatively, there is more than one kind of burst progenitor, some of which interact directly with the interstellar medium. Another proposed environment is a pulsar wind bubble that has expanded inside a supernova, which requires that the supernova precede the burst.

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The origin of Galactic cosmic rays as revealed by their composition

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab2533 ◽

2021 ◽

Vol 508 (1) ◽

pp. 1321-1345

Author(s):

Vincent Tatischeff ◽

John C Raymond ◽

Jean Duprat ◽

Stefano Gabici ◽

Sarah Recchia

Keyword(s):

Cosmic Rays ◽

Interstellar Medium ◽

Interstellar Dust ◽

Massive Star ◽

Gamma Ray ◽

Galactic Cosmic Rays ◽

Shock Acceleration ◽

Ionization State ◽

Hot Plasma ◽

Supernova Explosions

ABSTRACT Galactic cosmic rays (GCRs) are thought to be accelerated in strong shocks induced by massive star winds and supernova explosions sweeping across the interstellar medium. But the phase of the interstellar medium from which the CRs are extracted has remained elusive until now. Here, we study in detail the GCR source composition deduced from recent measurements by the AMS-02, Voyager 1, and SuperTIGER experiments to obtain information on the composition, ionization state, and dust content of the GCR source reservoirs. We show that the volatile elements of the CR material are mainly accelerated from a plasma of temperature ≳ 2 MK, which is typical of the hot medium found in Galactic superbubbles energized by the activity of massive star winds and supernova explosions. Another GCR component, which is responsible for the overabundance of 22Ne, most likely arises from acceleration of massive star winds in their termination shocks. From the CR-related gamma-ray luminosity of the Milky Way, we estimate that the ion acceleration efficiency in both supernova shocks and wind termination shocks is of the order of 10−5. The GCR source composition also shows evidence for a preferential acceleration of refractory elements contained in interstellar dust. We suggest that the GCR refractories are also produced in superbubbles, from shock acceleration and subsequent sputtering of dust grains continuously incorporated into the hot plasma through thermal evaporation of embedded molecular clouds. Our model explains well the measured abundances of all primary and mostly primary CRs from H to Zr, including the overabundance of 22Ne.

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High-energy Galactic phenomena and the interstellar medium

Symposium - International Astronomical Union ◽

10.1017/s0074180900242502 ◽

1985 ◽

Vol 106 ◽

pp. 225-233

Author(s):

Catherine J. Cesarsky

Keyword(s):

Magnetic Fields ◽

Interstellar Medium ◽

Molecular Hydrogen ◽

Gamma Ray ◽

Cosmic Ray ◽

High Energy ◽

Small Scale ◽

The Galaxy ◽

Γ Rays ◽

Γ Ray

Gamma rays of energy in the range 30 MeV-several GeV, observed by the satellites SAS-2 and COS-B, are emitted in the interstellar medium as a result of interactions with gas of cosmic-ray nuclei in the GeV range (π° decay γ rays) and cosmic-ray electrons of energy > 30 MeV (bremsstrahlung γ rays). W. Hermsen has presented at this conference the γ ray maps of the Galaxy in three “colours” constructed by the COS-B collaboration; the information in such maps is supplemented by radio-continuum studies (see lecture by R. Beck), and is a useful tool for studying the distribution of gas, cosmic rays (c.r.) and magnetic fields in the Galaxy. The variables in this problem are many:large-scale (~ 1 kpc) and small-scale (~10 pc) distributions of c.r. nuclei, of c.r. electrons, of atomic and molecular hydrogen, of magnetic fields, fraction of the observed radiation due to localized sources, etc. Of these, only the distribution - or at least the column densities - of atomic hydrogen are determined in a reliable way. Estimates of the amount of molecular hydrogen can be derived from CO observations or from galaxy counts. The radio and gamma-ray data are not sufficient to disentangle all the other variables in a unique fashion, unless a number of assumptions are made (e.g. Paul et al. 1976). Still, the COS-B team has been able to show that :a) there is a correlation between the gamma-ray emission from local regions, as observed at intermediate latitudes, and the total column density of dust, as measured by galaxy counts. The simplest interpretation is that the density of c.r. nuclei and electrons is uniform within 500 pc of the sun, and that dust and gas are well mixed. Then, γ rays can be used as excellent tracers of local gas complexes (Lebrun et al. 1982, Strong et al. 1982).b) In the same way, the simplest interpretation of the γ-ray emission at energy > 300 MeV from the inner Galaxy, is that c.r. nuclei and electrons are distributed uniformly as well : there is no need for an enhanced density of c.r. in the 3–6 kpc ring; on the contrary, even assuming a uniform density of c.r., the γ-ray data are in conflict with the highest estimates of molecular hydrogen in the radio-astronomy literature (Mayer-Hasselwander et al. 1982).c) In the outer Galaxy, the gradient of c.r. which had become apparent in the early SAS-2 data can now, with COS-B data, be studied in three energy ranges. A gradient in the c.r. distribution is only required to explain the low-energy radiation, which is dominated by bremsstrahlung from relativistic electrons (Bloemen et al., in preparation).

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Molecular Clouds Within 100 pc

International Astronomical Union Colloquium ◽

10.1017/s0252921100098250 ◽

1984 ◽

Vol 81 ◽

pp. 229-234

Author(s):

Leo Blitz ◽

Loris Magnani ◽

Lee Mundy

Keyword(s):

Interstellar Medium ◽

Molecular Hydrogen ◽

Molecular Clouds ◽

Milky Way ◽

Velocity Dispersion ◽

Scale Height ◽

Galactic Latitude ◽

Local Interstellar Medium ◽

High Galactic Latitude ◽

The Mean

AbstractObservations at the 2.6 mm line of CO reveal the presence of a large number of molecular clouds at high galactic latitude. If the velocity dispersion of the clouds is a measure of their scale height, the mean distance of the ensemble we have detected is 100 pc. The clouds are unusual in that either they are not gravitationally bound or they are very deficient in CO relative to molecular hydrogen. These clouds represent a heretofore unrecognized component of the local interstellar medium. If they are pervasive in the Milky Way, they probably represent the small molecular cloud component of the interstellar medium.

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On the Flaring of Thick Discs of Galaxies: Insights from Simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3906 ◽

2020 ◽

Author(s):

Joaquín García de la Cruz ◽

Marie Martig ◽

Ivan Minchev ◽

Philip James

Keyword(s):

Surface Density ◽

Milky Way ◽

Large Fraction ◽

High Surface ◽

Scale Height ◽

The Other ◽

Height Distribution ◽

Thick Disc ◽

Cosmological Context ◽

The Vertical Distribution

Abstract Using simulated galaxies in their cosmological context, we analyse how the flaring of mono-age populations (MAPs) influences the flaring and the age structure of geometrically-defined thick discs. We also explore under which circumstances the geometric thin and thick discs are meaningfully distinct components, or are part of a single continuous structure as in the Milky Way. We find that flat thick discs are created when MAPs barely flare or have low surface density at the radius where they start flaring. When looking at the vertical distribution of MAPs, these galaxies show a continuous thin/thick structure. They also have radial age gradients and tend to have quiescent merger histories. Those characteristics are consistent with what is observed in the Milky Way. Flared thick discs, on the other hand, are created when the MAPs that flare have a high surface density at the radius where they start flaring. The thick discs’ scale-heights can either be dominated by multiple MAPs or just a few, depending on the mass and scale-height distribution of the MAPs. In a large fraction of these galaxies, thin and thick discs are clearly distinct structures. Finally, flared thick discs have diverse radial age gradients and merger histories, with galaxies that are more massive or that have undergone massive mergers showing flatter age radial gradients in their thick disc.

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Galactic 26Al traces metal loss through hot chimneys

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3612 ◽

2020 ◽

Vol 501 (1) ◽

pp. 210-218

Author(s):

Martin G H Krause ◽

Donna Rodgers-Lee ◽

James E Dale ◽

Roland Diehl ◽

Chiaki Kobayashi

Keyword(s):

Galaxy Evolution ◽

Massive Star ◽

Milky Way ◽

Gamma Ray ◽

Branching Ratio ◽

Metal Loss ◽

Global Flow ◽

Model Galaxy ◽

Simulation Results ◽

Supernova Feedback

ABSTRACT Radioactive 26Al is an excellent tracer for metal ejection in the Milky Way, and can provide a direct constraint on the modelling of supernova feedback in galaxy evolution. Gamma-ray observations of the 26Al decay line have found high velocities and hence require a significant fraction of the Galactic 26Al in the hot component. At the same time, meteoritic data combined with simulation results suggest that a significant amount of 26Al makes its way into stars before decay. We investigated the distribution into hot and cold channels with a simulation of a Milky-Way-like galaxy with massive-star feedback in superbubbles and with ejecta traced by 26Al. About 30–40 per cent of the ejecta remain hot, with typical cooling times of the order Gyr. 26Al traces the footpoints of a chimney-fed outflow that mixes metals turbulently into the halo of the model galaxy on a scale of at least 50 kpc. The rest diffuses into cold gas ≲ 104 K, and may therefore be quickly available for star formation. We discuss the robustness of the result by comparison to a simulation with a different global flow pattern. The branching ratio into hot and cold components is comparable to that of longer term average results from chemical evolution modelling of galaxies, clusters, and the intracluster medium.

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26 Al Radioactivity in the Galaxy

International Astronomical Union Colloquium ◽

10.1017/s0252921100071311 ◽

1997 ◽

Vol 166 ◽

pp. 393-396 ◽

Cited By ~ 1

Author(s):

R. Diehl ◽

U. Oberlack ◽

J. Knödlseder ◽

K. Bennett ◽

H. Bloemen ◽

...

Keyword(s):

Interstellar Medium ◽

Decay Time ◽

Time Scale ◽

Large Scale ◽

Massive Star ◽

Spiral Structure ◽

Massive Stars ◽

Scale Height ◽

Imaging Results ◽

The Galaxy

Abstract26Al radioactivity is believed to originate predominantly from massive stars, ejected into interstellar medium in wind phases and/or supernova events. With its million-year decay time, penetrating γ-rays from 26Al decay measure the massive-star history averaged over a time scale of ≃million years, thus extending times cales accessible otherwise. The COMPTEL 1.809 MeV all-sky data from 5 years of observations show irregularities and features at intermediate latitudes, which may have a more local origin (≃ 1 kpc). We find that the large scale emission can be characterized by a Galactic scale height of ≃ 130 pc, and a Galactocentric scale radius of ≃ 5 kpc, with features from spiral structure. Catalogues from massive-star related objects do not significantly improve the description of COMPTEL data above this. Emission associated with nearby structures such as the Gould Belt, Loop I, or stellar aggregates, is indicated, yet cannot be clearly detected. Combined with our imaging results, this suggests that 26A1 yields from massive star ensembles depend on specifics of those stars and their history. Further 26A1 γ-ray studies are underway to help mapping of the massive star history in the solar vicinity.

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