scholarly journals Diffusion of cosmic-ray electrons in the Galactic centre molecular cloud G0.13–0.13

2013 ◽  
Vol 9 (S303) ◽  
pp. 434-438
Author(s):  
Andrew Lehmann ◽  
Mark Wardle
Keyword(s):  
Molecular Cloud ◽  
Galactic Center ◽  
Galactic Disk ◽  
Line Emission ◽  
Cosmic Ray ◽  
Diffusion Models ◽  
Low Energy ◽  
Shell Morphology ◽  
Galactic Centre ◽  
Heating Rates

AbstractThe Galactic center (GC) molecular cloud G0.13–0.13 exhibits a shell morphology in CS J = (1 − 0), with ∼ 105 solar masses and expansion speed ∼ 20 km s−1, yielding a total kinetic energy ∼ 1051 erg. Its morphology is also suggestive of an interaction with the nonthermal filaments of the GC arc. 74 MHz emission indicates the presence of a substantial population of low energy electrons permeating the cloud, which could either be produced by the interaction with the arc or accelerated in the shock waves responsible for the cloud's expansion. These scenarios are explored using time dependent diffusion models.With these diffusion models, we determine the penetration of low-energy cosmic-ray electrons accelerated into G0.13–0.13 and calculate the spatial distribution of the cosmic-ray ionization and heating rates. We show that the 6.4 keV Fe Kα line emission associated with the electron population provides an observational diagnostic to distinguish these two acceleration scenarios.We discuss the implications of our results for understanding the distinct character of clouds in the central molecular zone compared to clouds in the Galactic disk, and how GC nonthermal filaments interact with molecular clouds.

The Origin of X-Ray Emission from a Galactic Center Molecular Cloud: Low-Energy Cosmic-Ray Electrons

2002 ◽  
Vol 568 (2) ◽  
pp. L121-L125 ◽  
Author(s):  
F. Yusef-Zadeh ◽  
C. Law ◽  
M. Wardle
Keyword(s):  
Molecular Cloud ◽  
Galactic Center ◽  
Cosmic Ray ◽  
Low Energy ◽  
X Ray

scholarly journals Contribution of the Galactic centre to the local cosmic-ray flux

2018 ◽  
Vol 619 ◽  
pp. A12 ◽  
Author(s):  
Étienne Jaupart ◽  
Étienne Parizot ◽  
Denis Allard
Keyword(s):  
Galactic Disk ◽  
A Priori ◽  
Cosmic Ray ◽  
High Energy ◽  
Single Type ◽  
Galactic Centre ◽  
High Energy Particle ◽  
The Galaxy ◽  
Injection Power ◽  
Galactic Cosmic Ray

Context. Recent observations of unexpected structures in the Galactic cosmic ray (GCR) spectrum and composition, as well as growing evidence for episodes of intense dynamical activity in the inner regions of the Galaxy, call for an evaluation of the high-energy particle acceleration associated with such activity and its potential impact on the global GCR phenomenology. Aims. We investigate whether particles accelerated during high-power episodes around the Galactic centre can account for a significant fraction of the observed GCRs, or, conversely, what constraints can be derived regarding their Galactic transport if their contributions are negligible. Methods. Particle transport in the Galaxy is described with a two-zone analytical model. We solved for the contribution of a Galactic centre cosmic-Ray (GCCR) source using Green functions and Bessel expansion, and discussed the required injection power for these GCCRs to influence the global GCR phenomenology at Earth. Results. We find that, with standard parameters for particle propagation in the galactic disk and halo, the GCCRs can make a significant or even dominant contribution to the total CR flux observed at Earth. Depending on the parameters, such a source can account for both the observed proton flux and boron-to-carbon ratio (in the case of a Kraichnan-like scaling of the diffusion coefficient), or potentially produce spectral and composition features. Conclusions. Our results show that the contribution of GCCRs cannot be neglected a priori, and that they can influence the global GCR phenomenology significantly, thereby calling for a reassessement of the standard inferences from a scenario where GCRs are entirely dominated by a single type of sources distributed throughout the Galactic disk.

Galactic ?-ray Lines Resulting from Interactions Between Low Energy Cosmic Rays and the Interstellar Medium

1979 ◽  
Vol 32 (4) ◽  
pp. 383 ◽  
Author(s):  
Masato Yoshimori
Keyword(s):  
Cosmic Rays ◽  
Supernova Remnants ◽  
Galactic Plane ◽  
Crab Nebula ◽  
Cosmic Ray ◽  
Low Energy ◽  
Longitudinal Distribution ◽  
Galactic Centre ◽  
Interstellar Space ◽  
Interstellar Gas

Calculated spectral profiles and galactic distributions are presented for y-ray lines resulting from interactions between low energy cosmic rays and the interstellar gas and dust. Calculated local intensities are also presented for y-ray lines from discrete sources such as supernova remnants and dense interstellar gas clouds. The y-ray lines from excited dust nuclei (which have long mean lifetimes) are sharp, having widths of the order of a few keV; the lines from excited gas nuclei are relatively narrow, having widths of the order of 100 keV; and the lines from excited cosmic ray nuclei are broad, having widths of the order of 1 MeV. The longitudinal distribution of y-ray lines in the galactic plane shows a significant concentration toward the galactic centre, and a rapid falloff beyond I;. 50�. The most intense y-ray lines arise from positron annihilation (0�511 MeV) and the deexcitation of 12C* (4�439 MeV) and 160* (6�131 MeV). In the direction of the galactic centre, these lines have estimated intensities of the order of 10-5 photons cm-2s-1rad- 1, and so they may be resolved from the diffuse y-ray background there by observing with a high resolution Ge(Li) detector. In the direction of several strong discrete sources, the estimated fluxes are generally lower: ~10-6 photons cm-2s-1 for the Crab Nebula and the Vela pulsar, ~10-8 photons cm-2 s-1 for the interstellar dense cloud pOph, but ~10-5 photons cm-2 s-1 for the ring cloud around the galactic centre. The calculated intensities of various other y-ray lines are compared with available experimental data, and their detectability is considered. The implication of the galactic distribution of low energy cosmic rays for the gas density of the interstellar space through which the cosmic rays propagate is also discussed.

scholarly journals Disk-halo interactions: molecular clouds in the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 177-181
Author(s):  
D. Riquelme ◽  
J. Martín-Pintado ◽  
R. Mauersberger ◽  
S. Martín ◽  
L. Bronfman
Keyword(s):  
Molecular Cloud ◽  
Molecular Clouds ◽  
Large Scale ◽  
Galactic Center ◽  
Galactic Disk ◽  
Isotopic Ratio ◽  
Small Scale ◽  
Kinetic Temperature ◽  
Temperature Regimes ◽  
Gas Accretion

AbstractWe study the disk-halo interaction, in the context of orbits and Giant Molecular loops (GMLs) in the Galactic center (GC) region. From a large scale survey of the central kpc of the Galaxy, in SiO J = (2 − 1), HCO+J = (1 − 0) and H13CO+J = (1 − 0) molecular emission, we identify shock regions traced by the enhancement of the SiO. These positions were studied using the 12C/13C isotopic ratio to trace gas accretion/ejection. We found a systematically higher 12C/13C isotopic ratio (> 40) toward the GMLs and the x1 orbits than for the GC standard molecular clouds (20–25). The high isotopic ratios are consistent with the accretion of the gas from the halo and from the outskirts of the Galactic disk. From multi-transitional observations of NH3, we derive two kinetic temperature regimes (one warm at ∼150 K and one cold at ∼40 K) for all the positions, except for the GMLs positions where only the warm component is present. The fractional abundances derived from the different molecules support the shock origin for the heating mechanism in the GC. We also present a detailed study of one molecular cloud placed in the foot points of two giant molecular loops, where two of the previously selected positions are placed. Using the 22m Mopra telescope we mapped the molecular cloud M − 3.8 + 0.9 in 3-mm molecular lines. The data show structures at small scale in SiO emission, with narrower line profiles than those of, e.g, HCO+ or HCN, which indicate that the shocks are dynamically confined. The data also show clear differences between different molecular tracers, e.g., between the SiO and HCO+ emission, which would indicate differences in the physical properties and chemistry within the cloud.

scholarly journals MeV Gamma Ray Observational Constraints on the Galactic Center Region

1989 ◽  
Vol 136 ◽  
pp. 617-625
Author(s):  
R. Diehl ◽  
P. v.Ballmoos ◽  
V. Schönfelder ◽  
G. E. Morfill
Keyword(s):  
Gamma Ray ◽  
Galactic Center ◽  
Line Emission ◽  
Cosmic Ray ◽  
Time Variable ◽  
Observational Constraints ◽  
Annihilation Radiation ◽  
The Galaxy ◽  
Compton Telescope ◽  
Excitation Parameters

MPE Compton Telescope observations of MeV radiation from the direction of the Galactic Center result in constraints on the central gamma-ray source in the Galaxy: The extent of 1.8 MeV line emission from26Al suggests an26Al production process with pronounced concentration towards the Galactic Center. The absence of other gamma-ray lines constrains nucleosynthesis and cosmic ray excitation parameters in the Galaxy. Calculations demonstrate that time variable Galactic Center annihilation radiation may be related to a central26Al source.

scholarly journals 4.13. A high velocity molecular cloud near the center of the Galaxy

1998 ◽  
Vol 184 ◽  
pp. 193-194 ◽  
Author(s):  
Tomoharu Oka ◽  
Tetsuo Hasegawa ◽  
Glenn J. White ◽  
Fumio Sato ◽  
Masato Tsuboi ◽  
...  
Keyword(s):  
High Velocity ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Galactic Center ◽  
Galactic Disk ◽  
External Pressure ◽  
Galactic Bulge ◽  
Physical Conditions ◽  
Large Velocity ◽  
The Galaxy

Molecular clouds in the Galactic center region are characterised by their large velocity widths and physical conditions which differ from clouds in the Galactic disk (e.g., Morris 1996). These clouds may not be gravitationally bound, but in equilibrium with the high external pressure in the Galactic bulge (Spergel & Blitz 1992, Oka et al. 1997a).

scholarly journals Cosmic-Ray Transport in Simulations of Star-forming Galactic Disks

2021 ◽  
Vol 922 (1) ◽  
pp. 11
Author(s):  
Lucia Armillotta ◽  
Eve C. Ostriker ◽  
Yan-Fei Jiang
Keyword(s):  
Cosmic Rays ◽  
Galactic Disk ◽  
Effective Diffusion ◽  
Cosmic Ray ◽  
High Energy ◽  
Low Energy ◽  
Scattering Coefficient ◽  
Alfven Wave ◽  
High Energy Cosmic Rays ◽  
Scattering Rate

Abstract Cosmic-ray transport on galactic scales depends on the detailed properties of the magnetized, multiphase interstellar medium (ISM). In this work, we postprocess a high-resolution TIGRESS magnetohydrodynamic simulation modeling a local galactic disk patch with a two-moment fluid algorithm for cosmic-ray transport. We consider a variety of prescriptions for the cosmic rays, from a simple, purely diffusive formalism with constant scattering coefficient, to a physically motivated model in which the scattering coefficient is set by the critical balance between streaming-driven Alfvén wave excitation and damping mediated by local gas properties. We separately focus on cosmic rays with kinetic energies of ∼1 GeV (high-energy) and ∼30 MeV (low energy), respectively important for ISM dynamics and chemistry. We find that simultaneously accounting for advection, streaming, and diffusion of cosmic rays is crucial for properly modeling their transport. Advection dominates in the high-velocity, low-density hot phase, while diffusion and streaming are more important in higher-density, cooler phases. Our physically motivated model shows that there is no single diffusivity for cosmic-ray transport: the scattering coefficient varies by four or more orders of magnitude, maximal at density n H ∼ 0.01 cm−3. The ion-neutral damping of Alfvén waves results in strong diffusion and nearly uniform cosmic-ray pressure within most of the mass of the ISM. However, cosmic rays are trapped near the disk midplane by the higher scattering rate in the surrounding lower-density, higher-ionization gas. The transport of high-energy cosmic rays differs from that of low-energy cosmic rays, with less effective diffusion and greater energy losses for the latter.

scholarly journals Galactic line emission from 1–10 keV

1970 ◽  
Vol 37 ◽  
pp. 385-391
Author(s):  
Gary Steigman ◽  
Joseph Silk
Keyword(s):  
Excited States ◽  
Electron Capture ◽  
Ground State ◽  
Galactic Plane ◽  
Line Emission ◽  
Cosmic Ray ◽  
Low Energy ◽  
X Rays ◽  
Capture Process ◽  
Line Intensities

Calculations are given of K-series X-rays produced by interaction of both low energy cosmic rays and diffuse X-rays above 1 keV with heavier ions present in Hi regions. We further consider electron capture to excited states by cosmic ray nuclei of heavy elements, followed by cascades down to the ground state. It is found that the electron capture process may yield appreciable line intensities in the 1–10 keV range in the galactic plane.

scholarly journals SAS-2 gamma ray observations related to a galactic halo

1979 ◽  
Vol 84 ◽  
pp. 483-484
Author(s):  
C. E. Fichtel ◽  
G. A. Simpson ◽  
D. J. Thompson
Keyword(s):  
Energy Spectrum ◽  
Galactic Halo ◽  
Galactic Center ◽  
Galactic Disk ◽  
Cosmic Ray ◽  
Average Intensity ◽  
General Direction ◽  
Γ Radiation ◽  
The Galaxy ◽  
Γ Ray

An examination of the intensity, energy spectrum, and spatial distribution of the diffuse γ radiation observed by SAS 2 away from the galactic plane in the energy range above 35 MeV has revealed no evidence supporting a cosmic ray halo surrounding the galaxy in the general shape of a sphere. The diffuse γ radiation does consist of two components. One component is related to the galactic disk on the basis of its correlation with the 21-cm measurements, the continuum radio emission, and galactic coordinates. Further its energy spectrum is similar to that in the plane, and its intensity distribution joins smoothly to the intense radiation from the plane. The other component appears isotropic, at least on a coarse scale, and has a steep energy spectrum. The degree of isotropy which has been established for the “isotropic” radiation and the steep energy spectrum, which distinguishes it from the galactic disk radiation, place strong constraints on galactic halo models for the origin of this component. Theoretical models involving a galactic halo have generally postulated a halo with dimensions of the order of the Galaxy and hence a radius, at least in the plane, of about 15 kpcs. Since the Sun is about 10 kpc from the galactic center, if such a halo exists and is responsible for the γ rays (through, for example, black body Compton radiation), a very marked anisotropy would be seen, with the γ ray intensity from the general direction of the galactic center being much larger than that from the same latitudes in the anticenter direction. In fact, no such anisotropy is seen; specifically the ratio of the average intensity in the (300° < ℓ < 60°, 20° < |b| < 40°) region to that in the (100° < ℓ < 250°, 20° < |b| < 40°) region was found to be 1.10±0.19 compared to a calculated value for a model with a uniform cosmic ray sphere with a 15 kpc radius of 2.85. The ratio between the average γ-ray intensity from regions with |b| < 60° to that from 20° < |b| < 40° is found to be 0.87±0.09. If the region is assumed to be spherical, but with a larger radius and a uniform cosmic ray density, the upper limit (2σ) set for the anisotropy demands that the radius be at least 45 kpc. An extragalactic origin for the isotropic component currently appears to be a more plausible explanation.

scholarly journals The galactic magnetic field derived from cosmic-ray electrons

1968 ◽  
Vol 46 (10) ◽  
pp. S642-S645 ◽  
Author(s):  
H. Okuda ◽  
Y. Tanaka
Keyword(s):  
Magnetic Field ◽  
Solar System ◽  
Electron Spectrum ◽  
Galactic Center ◽  
Galactic Disk ◽  
Cosmic Ray ◽  
Field Configuration ◽  
Galactic Magnetic Field ◽  
Upper Limits ◽  
The Magnetic Field

An estimate of the galactic magnetic field is obtained by combining new results in the cosmic-ray electron spectrum and the recent radio data. The lower and upper limits of the magnetic field in the galactic disk are derived from two alternative models of field configuration; i.e. (0.5–1.0) × 10−5 gauss near the solar system and (1.0–2.0) × 10−5 gauss near the galactic center, respectively. The magnetic field in the halo is estimated to be larger than 2.5 × 10−6 gauss.

Sign in / Sign up

Export Citation Format

Share Document