scholarly journals Cosmic-ray ionisation in circumstellar discs

2018 ◽  
Vol 614 ◽  
pp. A111 ◽  
Author(s):  
Marco Padovani ◽  
Alexei V. Ivlev ◽  
Daniele Galli ◽  
Paola Caselli
Keyword(s):  
Molecular Clouds ◽  
Column Density ◽  
Cosmic Ray ◽  
Galactic Cosmic Rays ◽  
Charged Dust ◽  
Interstellar Gas ◽  
Complex Behaviour ◽  
Electron Positron ◽  
Fractional Abundance ◽  
Ionisation Rate

Context. Galactic cosmic rays (CRs) are a ubiquitous source of ionisation of the interstellar gas, competing with UV and X-ray photons as well as natural radioactivity in determining the fractional abundance of electrons, ions, and charged dust grains in molecular clouds and circumstellar discs. Aims. We model the propagation of various components of Galactic CRs versus the column density of the gas. Our study is focussed on the propagation at high densities, above a few g cm−2, especially relevant for the inner regions of collapsing clouds and circumstellar discs. Methods. The propagation of primary and secondary CR particles (protons and heavier nuclei, electrons, positrons, and photons) is computed in the continuous slowing down approximation, diffusion approximation, or catastrophic approximation by adopting a matching procedure for the various transport regimes. A choice of the proper regime depends on the nature of the dominant loss process modelled as continuous or catastrophic. Results. The CR ionisation rate is determined by CR protons and their secondary electrons below ≈130 g cm−2 and by electron-positron pairs created by photon decay above ≈600 g cm−2. We show that a proper description of the particle transport is essential to compute the ionisation rate in the latter case, since the electron and positron differential fluxes depend sensitively on the fluxes of both protons and photons. Conclusions. Our results show that the CR ionisation rate in high-density environments, such as the inner parts of collapsing molecular clouds or the mid-plane of circumstellar discs, is higher than previously assumed. It does not decline exponentially with increasing column density, but follows a more complex behaviour because of the interplay of the different processes governing the generation and propagation of secondary particles.

scholarly journals On the Cosmic Ray-Induced Ionization Rate in Molecular Clouds

2011 ◽  
Vol 2011 ◽  
pp. 1-10 ◽  
Author(s):  
Ararat G. Yeghikyan
Keyword(s):  
Molecular Clouds ◽  
Column Density ◽  
Cosmic Ray ◽  
Ionization Rate ◽  
Electronic Interaction ◽  
Absorbing Medium ◽  
Be Star ◽  
Good Agreement ◽  
Ionization Rates

The transformation of the energy dependence of the cosmic ray proton flux in the keV to GeV region is investigated theoretically when penetrating inside molecular clouds ( mag). The computations suggest that energy losses of the cosmic ray particles by interaction with the matter of the molecular cloud are principally caused by the inelastic (electronic) interaction potential; the transformed energy distribution of energetic protons is determined mainly by the column density of the absorbing medium. A cutoff of the cosmic ray spectrum inside clouds by their magnetic fields is also phenomenologically taken into account. This procedure allows a determination of environment-dependent ionization rates of molecular clouds. The theoretically predicted ionization rates are in good agreement with those derived from astronomical observations of absorption lines in the spectrum of the cloud connected with the Herbig Be star LkH 101.

scholarly journals Production of atomic hydrogen by cosmic rays in dark clouds

2018 ◽  
Vol 619 ◽  
pp. A144 ◽  
Author(s):  
Marco Padovani ◽  
Daniele Galli ◽  
Alexei V. Ivlev ◽  
Paola Caselli ◽  
Andrea Ferrara
Keyword(s):  
Cosmic Rays ◽  
Atomic Hydrogen ◽  
Molecular Hydrogen ◽  
Molecular Clouds ◽  
Cosmic Ray ◽  
Galactic Cosmic Rays ◽  
Dissociation Rate ◽  
Low Energy ◽  
Hydrogen Atoms ◽  
Dark Clouds

Context. Small amounts of atomic hydrogen, detected as absorption dips in the 21 cm line spectrum, are a well-known characteristic of dark clouds. The abundance of hydrogen atoms measured in the densest regions of molecular clouds can only be explained by the dissociation of H2 by cosmic rays. Aims. We wish to assess the role of Galactic cosmic rays in the formation of atomic hydrogen, for which we use recent developments in the characterisation of the low-energy spectra of cosmic rays and advances in the modelling of their propagation in molecular clouds. Methods. We modelled the attenuation of the interstellar cosmic rays that enter a cloud and computed the dissociation rate of molecular hydrogen that is due to collisions with cosmic-ray protons and electrons as well as fast hydrogen atoms. We compared our results with the available observations. Results. The cosmic-ray dissociation rate is entirely determined by secondary electrons produced in primary ionisation collisions. These secondary particles constitute the only source of atomic hydrogen at column densities above ~1021 cm−2. We also find that the dissociation rate decreases with column density, while the ratio between the dissociation and ionisation rates varies between about 0.6 and 0.7. From comparison with observations, we conclude that a relatively flat spectrum of interstellar cosmic-ray protons, such as suggested by the most recent Voyager 1 data, can only provide a lower bound for the observed atomic hydrogen fraction. An enhanced spectrum of low-energy protons is needed to explain most of the observations. Conclusions. Our findings show that a careful description of molecular hydrogen dissociation by cosmic rays can explain the abundance of atomic hydrogen in dark clouds. An accurate characterisation of this process at high densities is crucial for understanding the chemical evolution of star-forming regions.

Observations of the 18.3-GHz Transition of C3H2 towards Sgr B2

1992 ◽  
Vol 10 (2) ◽  
pp. 113-117
Author(s):  
R.S. Peng ◽  
J.B. Whiteoak ◽  
J.E. Reynolds ◽  
T.B.H. Kuiper ◽  
W.L. Peters
Keyword(s):  
Optical Depth ◽  
Molecular Clouds ◽  
Column Density ◽  
Radial Velocities ◽  
Continuum Emission ◽  
Fractional Abundance ◽  
Right Ascension ◽  
The Continuum

AbstractWe have mapped the molecular clouds of Sgr B2 in the 110 → 101 ortho-transition of C3H2 at 18.3 GHz, using the 70-m NASA telescope at Tidbinbilla (beamwidth 55 arcsec). Three clouds show absorption against the Sgr B2 continuum emission at radial velocities of 50, 65 and 80 km s−1. The 65-km s−1 cloud covers most of the observed area (4 × 6 arcmin in right ascension and declination), has a peak optical depth of 2.7 and a corresponding C3H2 column density of 7.6 × 1015 cm−2. The C3H2 fractional abundance relative to H2 is 1.5 × 10−9. The 80-km s−1 cloud, located north of the Sgr B2 continuum peak, has a peak optical depth of 0.9 and a C3H2 column density of 1.9 × 1015 cm−2. The 50-km s−1 cloud is centred 2 arcmin south of the continuum peak; here the minimum optical depth of 0.5 yields a column density of 5.3 × 1014cm−2.

scholarly journals Giant Molecular Clouds as probes of of Galactic Cosmic Rays with Fermi-LAT

2019 ◽  
Vol 209 ◽  
pp. 01016
Author(s):  
Giada Peron ◽  
Felix Aharonian ◽  
Sabrina Casanova ◽  
Ruizhi Yang ◽  
Roberta Zanin
Keyword(s):  
Cosmic Rays ◽  
Molecular Clouds ◽  
Particle Density ◽  
High Energy ◽  
Galactic Cosmic Rays ◽  
Secondary Emission ◽  
Giant Molecular Clouds ◽  
Interstellar Gas ◽  
High Particle ◽  
Direct Measurements

Direct measurements of Cosmic Rays (CRs) can not extend much further than the Solar System. In order to probe the so-called “sea” of Galactic Cosmic Rays, one should rely on secondary emission. Gamma rays produced in the interstellar gas, when hit by high energy particles, trace the energy distribution of the parent CRs. Giant Molecular Clouds, being huge reservoirs of hydrogen, serve as perfect targets for interaction with CRs. The high particle density in these objects enables to have enhanced  emission from small isolated location, and hence to derive information about single spots of the Milky Way. We analyzed more than 9 years data of Fermi-LAT from 18 molecular clouds, located in different regions from 100 pc to more than 10 kpc from us, allowing us to have the most comprehensive study on Galactic Cosmic Rays from Molecular Clouds ever.

scholarly journals The low cosmic-ray density in the Polaris Flare

2021 ◽  
Vol 21 (10) ◽  
pp. 246
Author(s):  
Zhi-Wei Cui ◽  
Rui-Zhi Yang ◽  
Bing Liu
Keyword(s):  
Molecular Cloud ◽  
Molecular Clouds ◽  
Column Density ◽  
Galactic Plane ◽  
Cosmic Ray ◽  
Giant Molecular Cloud ◽  
Large Gradient ◽  
Ray Density ◽  
Density Map

Abstract We reported the γ-ray observation towards the giant molecular cloud Polaris Flare. Together with the dust column density map, we derived the cosmic ray (CR) density and spectrum in this cloud. Compared with the CR measured locally, the CR density in the Polaris Flare is significantly lower and the spectrum is softer. Such a different CR spectrum reveals either a rather large gradient of CR distribution in the direction perpendicular to the Galactic plane or a suppression of CR inside molecular clouds.

scholarly journals High-energy gamma rays and the large-scale distribution of gas and cosmic rays

1985 ◽  
Vol 106 ◽  
pp. 213-218
Author(s):  
W. Hermsen ◽  
J.B.G.M. Bloemen
Keyword(s):  
Cosmic Rays ◽  
Column Density ◽  
Large Scale ◽  
Gamma Ray ◽  
Cosmic Ray ◽  
High Energy ◽  
Interstellar Gas ◽  
Density Maps ◽  
Nuclear Component ◽  
Energy Gamma

The COS-B gamma-ray survey is compared with 12CO and HI surveys in a region containing the Orion complex and in the outer Galaxy. The observed gamma-ray intensities in the Orion region (100 MeV<E<5 GeV) can be ascribed to the interaction of uniformly distributed cosmic rays with the interstellar gas. Calibration of the ratio between H2 column-density and integrated CO line intensity resulted in the value: (3.0±0.7)x102 0 molecules cm-2K -1km -1s. In the outer Galaxy HI column-density maps in three galacto-centric distance ranges are used in combination with COS-B gamma-ray data to determine the radial distribution of the gamma-ray emissivity. A steep negative gradient of the emissivity for the 70 MeV-150 MeV range and an approximately constant (within ~20%) emissivity for the 300 MeV-5 GeV range is found. The result is interpreted as a strong decrease in the cosmic-ray electron density and a near constancy of the nuclear component.

scholarly journals The impact of astrophysical dust grains on the confinement of cosmic rays

2021 ◽  
Vol 502 (2) ◽  
pp. 2630-2644
Author(s):  
Jonathan Squire ◽  
Philip F Hopkins ◽  
Eliot Quataert ◽  
Philipp Kempski
Keyword(s):  
Cosmic Rays ◽  
Cosmic Ray ◽  
Galactic Cosmic Rays ◽  
Alfven Waves ◽  
Feedback Mechanism ◽  
Alfvén Waves ◽  
Small Scale ◽  
Charged Dust ◽  
Dust Grains ◽  
The Impact

ABSTRACT We argue that charged dust grains could significantly impact the confinement and transport of galactic cosmic rays. For sub-GeV to ∼103 GeV cosmic rays, small-scale parallel Alfvén waves, which isotropize cosmic rays through gyro-resonant interactions, are also gyro-resonant with charged grains. If the dust is nearly stationary, as in the bulk of the interstellar medium, Alfvén waves are damped by dust. This will reduce the amplitude of Alfvén waves produced by the cosmic rays through the streaming instability, thus enhancing cosmic ray transport. In well-ionized regions, the dust damping rate is larger by a factor of ∼10 than other mechanisms that damp parallel Alfvén waves at the scales relevant for ∼GeV cosmic rays, suggesting that dust could play a key role in regulating cosmic ray transport. In astrophysical situations in which the dust moves through the gas with super-Alfvénic velocities, Alfvén waves are rendered unstable, which could directly scatter cosmic rays. This interaction has the potential to create a strong feedback mechanism where dust, driven through the gas by radiation pressure, then strongly enhances the confinement of cosmic rays, increasing their capacity to drive outflows. This mechanism may act in the circumgalactic medium around star-forming galaxies and active galactic nuclei.

scholarly journals The interstellar medium in young supernova remnants: key to the production of cosmic X-rays and $\gamma $-rays

2021 ◽  
Vol 366 (6) ◽  
Author(s):  
Hidetoshi Sano ◽  
Yasuo Fukui
Keyword(s):  
Interstellar Medium ◽  
Supernova Remnants ◽  
Cosmic Ray ◽  
High Energy ◽  
X Rays ◽  
Interstellar Gas ◽  
High Energy Radiation ◽  
Dense Cores ◽  
The Relationship ◽  
Turbulent Velocity Field

AbstractWe review recent progress in elucidating the relationship between high-energy radiation and the interstellar medium (ISM) in young supernova remnants (SNRs) with ages of ∼2000 yr, focusing in particular on RX J1713.7−3946 and RCW 86. Both SNRs emit strong nonthermal X-rays and TeV $\gamma $ γ -rays, and they contain clumpy distributions of interstellar gas that includes both atomic and molecular hydrogen. We find that shock–cloud interactions provide a viable explanation for the spatial correlation between the X-rays and ISM. In these interactions, the supernova shocks hit the typically pc-scale dense cores, generating a highly turbulent velocity field that amplifies the magnetic field up to 0.1–1 mG. This amplification leads to enhanced nonthermal synchrotron emission around the clumps, whereas the cosmic-ray electrons do not penetrate the clumps. Accordingly, the nonthermal X-rays exhibit a spatial distribution similar to that of the ISM on the pc scale, while they are anticorrelated at sub-pc scales. These results predict that hadronic $\gamma $ γ -rays can be emitted from the dense cores, resulting in a spatial correspondence between the $\gamma $ γ -rays and the ISM. The current pc-scale resolution of $\gamma $ γ -ray observations is too low to resolve this correspondence. Future $\gamma $ γ -ray observations with the Cherenkov Telescope Array will be able to resolve the sub-pc-scale $\gamma $ γ -ray distribution and provide clues to the origin of these cosmic $\gamma $ γ -rays.

scholarly journals Measurement of the cosmic ray proton spectrum from 40 GeV to 100 TeV with the DAMPE satellite

2019 ◽  
Vol 5 (9) ◽  
pp. eaax3793 ◽  
Author(s):  
◽  
Q. An ◽  
R. Asfandiyarov ◽  
P. Azzarello ◽  
P. Bernardini ◽  
...  
Keyword(s):  
Cosmic Rays ◽  
Cosmic Radiation ◽  
Precise Measurement ◽  
Milky Way ◽  
Spectral Feature ◽  
Dark Matter Particle ◽  
Cosmic Ray ◽  
Galactic Cosmic Rays ◽  
Proton Spectrum ◽  
First Time

The precise measurement of the spectrum of protons, the most abundant component of the cosmic radiation, is necessary to understand the source and acceleration of cosmic rays in the Milky Way. This work reports the measurement of the cosmic ray proton fluxes with kinetic energies from 40 GeV to 100 TeV, with 2 1/2 years of data recorded by the DArk Matter Particle Explorer (DAMPE). This is the first time that an experiment directly measures the cosmic ray protons up to ~100 TeV with high statistics. The measured spectrum confirms the spectral hardening at ~300 GeV found by previous experiments and reveals a softening at ~13.6 TeV, with the spectral index changing from ~2.60 to ~2.85. Our result suggests the existence of a new spectral feature of cosmic rays at energies lower than the so-called knee and sheds new light on the origin of Galactic cosmic rays.

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