We explore the impact of diffusive cosmic rays (CRs) on the evolution of the interstellar medium (ISM) under varying assumptions of supernova explosion environment. In practice, we systematically vary the relative fractions of supernovae (SN) occurring in star-forming high-density gas and those occurring in random locations decoupled from star-forming gas to account for SN from run-away stars or explosions in regions that have been cleared by prior SN, stellar winds, or radiation. We explore various mixed models by adjusting these fractions relative to each other. We find that in the simple system of a periodic stratified gas layer the ISM structure will evolve to one of two solutions: a "peak driving" state where warm gas is volume filling or a "thermal runaway" state where hot gas is volume filling. CR pressure and transport are important factors that strongly influence the solution state the ISM reaches and have the ability to flip the ISM between solutions. Observable signatures such as gamma ray emission and HI gas are explored. We find that gamma ray luminosity from pion decay is largely consistent with observations for a range of model parameters. The thickness of the HI gas layer may be too compact, however, this may be due to a large cold neutral fraction of midplane gas. The volume fraction of hot gas evolves to stable states in both solutions, but neither settles to a Milky Way-like configuration, suggesting that additional physics which is omitted here (e.g. a cosmological circum-galactic medium, radiation transport, or spectrally resolved and spatially varying CR transport) may be required.
Cosmic-ray (CR) induced heating of whole interstellar grains is an important desorption mechanism for grain surface molecules in interstellar molecular clouds. This study aims to provide a detailed temperature spectra for such CR-induced heating. For this, olivine grains with radius of 0.05, 0.1 and 0.2 microns shielded by interstellar gas with isotropic column densities characteristic to dark cores were considered. The accumulation of an ice mantle of increasing thickness was taken into account. The CR energy spectra was obtained for these column densities for 32 cosmic-ray constituents. We c…
Photodissociation of 14N2 and 14N15N occurs in interstellar clouds, circumstellar envelopes, protoplanetary discs, and other environments due to UV radiation from stellar sources and the presence of cosmic rays. This source of N atoms initiates the formation of complex N-bearing species and influences their isotopic composition. To study the photodissociation rates of 14N15N by UV continuum radiation and both isotopologues in a field of cosmic ray induced photons. To determine the effect of these on the isotopic composition of more complex molecules. High-resolution photodissociation cross sec…
We present a detailed morphological study of TeV gamma rays, synchrotron radiation, and interstellar gas in the young Type Ia supernova remnant (SNR) RCW 86. We find that the interstellar atomic gas shows good spatial correlation with the gamma rays, indicating that the TeV gamma rays from RCW 86 are likely to be dominantly of hadronic origin. In contrast, the spatial correlation between the interstellar molecular cloud and the TeV gamma rays is poor in the southeastern shell of the SNR. We argue that this poor correlation can be attributed to the low-energy cosmic rays (~ 1 TeV) not penetrati…
We discuss the relation between cosmic-ray induced interstellar gamma-ray and radio emission from our Galaxy, and emphasize the importance of their parallel study. We give an overview of results from Fermi-LAT on the interstellar gamma-ray emission, and then focus on complementary studies of the radio emission from the Galaxy.
An analysis of the energy spectra of cosmic rays and particularly the precise data from the AMS-02 experiment support the view about the important role of the Local Bubble in the nearby interstellar medium. It is suggested that the bulk of cosmic rays below about 200 GV of rigidity (momentum/charge ratio) comes from the modest number of supernova remnants in the Local Bubble which appear to have occurred some $10^6$ years ago and contributed to its formation. At higher rigidities the contribution from a 'Local Source', a single supernova remnant generated some $10^5$ years ago seems to dominat…
We review recent progress in elucidating the relationship between high-energy radiation and the interstellar medium (ISM) in young supernova remnants (SNRs) with ages of $\sim$2000 yr, focusing in particular on RX J1713.7$-$3946 and RCW 86. Both SNRs emit strong nonthermal X-rays and TeV $γ$-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…
Glycolaldehyde (HOCH2CHO) is the most straightforward sugar detected in the Interstellar Medium (ISM) and participates in the formation pathways of molecules fundamental to life, red such as ribose and derivatives. Although detected in several regions of the ISM, its formation route is still debated and its abundance cannot be explained only by reactions in the gas phase. This work explores a new gas-phase formation mechanism for glycolaldehyde and compares the energy barrier reduction when the same route happens on the surface of amorphous ices. The first step of the mechanism involves the fo…
Excess emission over expected diffuse astrophysical backgrounds in the direction of the Galactic center region has been claimed at various wavelengths, from radio to gamma rays. Among particle models advocated to explain such observations, several invoke interactions between dark matter particles and ordinary matter, such as cosmic rays, interstellar gas or free electrons. Depending on the specific interstellar matter particles' species and energy, such models predict distinct morphological features. In this study we make detailed predictions for the morphology of models where the relevant ele…
Recent measurements of cosmic gamma ray intensities up to TeV energies have been used to estimate the spectral shape of the parent cosmic ray particles present in the interstellar medium. The case is made for the particle spectrum in the Inner Galaxy being flatter than locally and in the Outer Galaxy. Of various possible explanations we make the case for the propagation of the particles being different in the more turbulent interstellar medium of the Inner Galaxy. The characteristic parameter alpha for the so called anomalous diffusion is expected to be less in the Inner Galaxy than that local…
We present a self-consistent interpretation of the of very-high-energy neutrino signal from the direction of the inner Galaxy, which is a part of the astronomical neutrino signal reported by IceCube. We demonstrate that an estimate of the neutrino flux in the E>100 TeV energy range lies at the high-energy power-law extrapolation of the spectrum of diffuse gamma-ray emission from the Galactic Ridge, as observed by Fermi telescope. This suggests that IceCube neutrino and Fermi/LAT gamma-ray fluxes are both produced in interactions of cosmic rays with the interstellar medium in the Norma arm and/…
The gamma-ray sky >100 MeV is dominated by the diffuse emissions from interactions of cosmic rays with the interstellar gas and radiation fields of the Milky Way. Observations of these diffuse emissions provide a tool to study cosmic-ray origin and propagation, and the interstellar medium. We present measurements from the first 21 months of the Fermi-LAT mission and compare with models of the diffuse gamma-ray emission generated using the GALPROP code. The models are fitted to cosmic-ray data and incorporate astrophysical input for the distribution of cosmic-ray sources, interstellar gas and r…
RX J1713.7-3946 is the most remarkable very-high-energy γ-ray supernova remnant which emits synchrotron X-rays without thermal features. We made a comparative study of CO, HI and X-rays in order to better understand the relationship between the X-rays, and the molecular and atomic gas. The results indicate that the X-rays are enhanced around the CO and HI clumps on a pc scale but are decreased inside the clumps on a 0.1 pc scale. Magnetohydrodynamic numerical simulations of the shock interaction with molecular and atomic gas indicate that the interaction between the shock waves and the clumps …
Observations by the Large Area Telescope (LAT) on the \textit{Fermi} mission of diffuse $γ$-rays in a mid-latitude region in the third quadrant (Galactic longitude $l$ from $200\arcdeg$ to $260\arcdeg$ and latitude $| b |$ from $22\arcdeg$ to $60\arcdeg$) are reported. The region contains no known large molecular cloud and most of the atomic hydrogen is within 1 kpc of the solar system. The contributions of $γ$-ray point sources and inverse Compton scattering are estimated and subtracted. The residual $γ$-ray intensity exhibits a linear correlation with the atomic gas column density in energy …
We study the destruction and modification of icy interstellar objects by cosmic rays and gas collisions. Using the cosmic-ray flux measured in the local interstellar medium as well as inferred from gamma-ray observations at the different galactocentric radii, we find that cosmic-ray erosion is significant for interstellar objects made of common types of ices. Interestingly, cosmic-ray heating might destroy icy interstellar objects very efficiently such that the initial size of an N$_2$ fragment as suggested by \citet{jackson2021} to explain the composition of `Oumuamua should be at least 0.5 k…
During the solar journey through galactic space, variations in the physical properties of the surrounding interstellar medium (ISM) modify the heliosphere and modulate the flux of galactic cosmic rays (GCR) at the surface of the Earth, with consequences for the terrestrial record of cosmogenic radionuclides. One phenomenon that needs studying is the effect on cosmogenic isotope production of changing anomalous cosmic ray fluxes at Earth due to variable interstellar ionizations. The possible range of interstellar ram pressures and ionization levels in the low density solar environment generate …
Icy grains in the interstellar medium and star-formation regions consist of a variety of materials. Such composite grains interact differently with cosmic-ray (CR) particles compared to simple single-material grains. We aim to calculate the spectra of energies and temperatures of mixed-composition grains undergoing whole-grain heating by CRs. The grains were assumed to consist of a mixture of carbon and olivine, covered by ices consisting of carbon oxides and water. The energy and temperature spectra for grains with radii 0.05; 0.1, and 0.2 microns impacted by CRs were calculated for eight val…
We present a new analysis of the interstellar protons toward the TeV $γ$-ray SNR RX J0852.0$-$4622 (G266.2$-$1.2, Vela Jr.). We used the NANTEN2 $^{12}$CO($J$ = 1-0) and ATCA & Parkes HI datasets in order to derive the molecular and atomic gas associated with the TeV $γ$-ray shell of the SNR. We find that atomic gas over a velocity range from $V_\mathrm{LSR}$ = $-4$ km s$^{-1}$ to 50 km s$^{-1}$ or 60 km s$^{-1}$ is associated with the entire SNR, while molecular gas is associated with a limited portion of the SNR. The large velocity dispersion of the HI is ascribed to the expanding motion of …
The interstellar molecular clouds are the site of star formation and also the target for the cosmic ray protons to produce γ-rays via the hadronic process. The interstellar atomic gas is enveloping the molecular clouds and may also be dense enough to affect the γ-ray production. In this Chapter, some of the basic properties of the interstellar gas both in molecular and atomic forms will be reviewed. Then, it is presented that two young TeV γ-ray SNRs, RX J1713.7-3946 and RX J0852.0-4622, show good spatial correspondence between the γ-rays and the interstellar protons. The good spatial correspo…
The interstellar medium is the engine room for galactic evolution. While much is known about the conditions within the ISM, many important areas regarding the formation and evolution of the various phases of the ISM leading to star formation, and its role in important astrophysical processes, remain to be explained. This paper discusses several of the fundamental science problems, placing them in context with current activities and capabilities, as well as the future capabilities that are needed to progress them in the decade ahead. Australia has a vibrant research community working on the int…
In this white paper we introduce the IMAGINE Consortium and its scientific background, goals and structure. Our purpose is to coordinate and facilitate the efforts of a diverse group of researchers in the broad areas of the interstellar medium, Galactic magnetic fields and cosmic rays, and our goal is to develop more comprehensive insights into the structures and roles of interstellar magnetic fields and their interactions with cosmic rays. To achieve a higher level of self-consistency, depth and rigour can only be achieved by the coordinated efforts of experts in diverse areas of astrophysics…
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 $\sim$MeV to $\sim$PeV lose energy and produce emissio…
The rate of ionization by cosmic rays in interstellar gas directly associated with gamma-ray emitting supernova remnants is for the first time calculated to be several orders of magnitude larger than the Galactic average. Analysis of ionization-induced chemistry yields the first quantitative prediction of the astrophysical H_{2}^{+} emission line spectrum, which should be detectable together with H_3^+ lines. The predicted coincident observation of those emission lines and gamma-rays will help prove that supernova remnants are sources of cosmic rays.
We have analyzed the atomic and molecular gas using the 21 cm HI and 2.6/1.3 mm CO emissions toward the young supernova remnant (SNR) RCW 86 in order to identify the interstellar medium with which the shock waves of the SNR interact. We have found an HI intensity depression in the velocity range between $-46$ and $-28$ km s$^{-1}$ toward the SNR, suggesting a cavity in the interstellar medium. The HI cavity coincides with the thermal and non-thermal emitting X-ray shell. The thermal X-rays are coincident with the edge of the HI distribution, which indicates a strong density gradient, while the…
Cosmic ray propagation is determined by the properties of interstellar turbulence. The multiphase nature of interstellar medium (ISM) and diversity of driving mechanisms give rise to spatial variation of turbulence properties. Meanwhile, precision astroparticle experiments pose challenges to the conventional picture of homogeneous and isotropic transport of cosmic rays (CRs). We are opening a new horizon for CR propagation research when studies of particle transport and interstellar turbulence confront each other. Here we review our recent developement on understandings of magnetohydrodynamic …
The abundances of gas and dust (solids and complex molecules) in the interstellar medium (ISM) as well as their composition and structures impact practically all of astrophysics. Fundamental processes from star formation to stellar winds to galaxy formation all scale with the number of metals. However, significant uncertainties remain in both absolute and relative abundances, as well as how these vary with environment, e.g., stellar photospheres versus the interstellar medium (ISM). While UV, optical, IR, and radio studies have considerably advanced our understanding of ISM gas and dust, they …
Cosmic Rays (CR) process the matter of the Interstellar Medium. Such energetic processing not only modifies the interstellar matter but also injects chemical species in the gas phase. In this work, we study the effect of the CR on the astrophysical polycyclic aromatic hydrocarbons (PAH). For events in which many electrons are stripped out from the PAH by interaction with a heavy cosmic ray particle, coulomb explosion takes place and carbon chains are produced. The fragments production rates of carbon chains are of particular interest for astrophysical models. We computed PAH multi-ionization c…
Interplay between Escaping Cosmic Rays and Interstellar Medium: Driving of Galactic Winds and Shaping the Local Proton Spectrum
Institute for Cosmic Ray Research, The University of Tokyo（东京大学宇宙射线研究所）；Department of Physics, Graduate School of Science, Nagoya University（名古屋大学理学研究科物理学系）
The formation of double and triple C-C bonds from the processing of pure c-C6H12 (cyclohexane) and mixed H2O:NH3:c-C6H12 (1:0.3:0.7) ices by highly-charged, and energetic ions (219 MeV O^{7+} and 632 MeV Ni^{24+}) is studied. The experiments simulate the physical chemistry induced by medium-mass and heavy-ion cosmic rays in interstellar ices analogs. The measurements were performed inside a high vacuum chamber at the heavy-ion accelerator GANIL (Grand Accelératéur National d'Ions Lourds) in Caen, France. The gas samples were deposited onto a polished CsI substrate previously cooled to 13 K. In…
The Parker instability, a Rayleigh-Taylor like instability of thermal gas supported against gravity by magnetic fields and cosmic rays, is thought to be dynamically important for galaxy evolution, possibly promoting molecular cloud formation and the galactic dynamo. In previous work, we examined the effect of three different cosmic ray transport models on the Parker instability: decoupled ($γ_c = 0$), locked to the thermal gas ($γ_c = 4/3$) and coupled to the gas with streaming by self-confinement. We expand upon that work here by considering radiative cooling, a smooth gravitational potential…
Some observations of warm carbon chain chemistry (WCCC) cores indicate that they are often located near the edges of molecular clouds. This finding may suggest that WCCC is promoted in star-forming cores exposed to radiation from the interstellar medium. We aim to investigate the chemistry of carbon chains in such a core. A chemical simulation of a gas parcel in a low-mass star-forming core with a full level of irradiation by interstellar photons and cosmic rays was compared to a simulation of a core receiving only one-tenth of such irradiation. In the full irradiation model, the abundances of…
School of Mathematics and Physics, Anhui Jianzhu University（安徽建筑大学数学与物理学院）；Department of Physics and Astronomy, University of Missouri（密苏里大学物理与天文学系）；Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所粒子天体物理重点实验室）
We modelled recent observations of UV absorption of HD and \HH\ in the Milky Way and toward damped/sub-damped Lyman alpha systems at z=0.18 and z $>$ 1.7. N(HD)/N(\HH) ratios reflect the separate self-shieldings of HD and \HH\ and the coupling introduced by deuteration chemistry. Locally, observations are explained by diffuse molecular gas with $ 16 \pccc \la$ n(H) $\la 128 \pccc $ if the cosmic-ray ionization rate per H-nucleus \zetaH $= 2\times 10^{-16}\ps$ as inferred from \H3\p\ and OH\p. The dominant influence on N(HD)/N(\HH) is the cosmic-ray ionization rate with a much weaker downward d…
A field with particularly exciting results over the past few years is the study of the interaction of cosmic rays with interstellar matter. For star formation to take place, gas and dust need to be sufficiently cold for gravity to overcome thermal pressure, and the ionisation fraction must be low enough to enable substantial decoupling between the gas and the Galactic magnetic field. As soon as the visual extinction is of the order of 3-4 magnitudes, the ultraviolet photon flux from the interstellar radiation field is fully quenched, thus the only source of ionisation and heating is provided b…
Cosmic rays in the energy range from about 10's GeV to several 100's TeV are observed on Earth with an energy-dependent anisotropy of order 0.01-0.1%, and a consistent topology that appears to significantly change at higher energy. The nearest and most recent galactic cosmic ray sources might stochastically dominate the observation and possibly explain a change in orientation of the anisotropy as a function of energy. However, the diffusion approximation is not able to explain its non-dipolar structure and, in particular, the significant contribution of small angular scale features. Particle p…
Direct measurements of cosmic ray (CR) species combined with observations of their associated gamma-ray emissions can be used to constrain models of CR propagation, trace the structure of the Galaxy, and search for signatures of new physics. The spatial density distribution of the interstellar gas is a vital element for all these studies. So far models have employed the 2D cylindrically symmetric geometry, but their accuracy is well behind that of the available data. In this paper, 3D spatial density models for the neutral and molecular hydrogen are constructed based on empirical model fitting…
Measurements of the lithium isotopic ratio in the diffuse interstellar medium from high-resolution spectra of the LiI λ6708 resonance doublet have now been reported for a number of lines of sight. The majority of the results for the 7Li/6Li ratio are similar to the Solar System ratio of 12.2 but the line of sight toward o Per, a star near the star-forming region IC 348, gave a ratio of about 2, the expected value for gas exposed to spallation and fusion reactions driven by cosmic rays. To examine the association of IC 348 with cosmic rays more closely, we measured the lithium isotopic ratio fo…
We derive the magnitude of fluctuations in total synchrotron intensity in the Milky Way and M33, from both observations and theory under various assumption about the relation between cosmic rays and interstellar magnetic fields. Given the relative magnitude of the fluctuations in the Galactic magnetic field (the ratio of the rms fluctuations to the mean magnetic field strength) suggested by Faraday rotation and synchrotron polarization, the observations are inconsistent with local energy equipartition between cosmic rays and magnetic fields. Our analysis of relative synchrotron intensity fluct…
In the absence of magnetic fields and cosmic rays, radiative cooling laws with a range of dependences on temperature affect the stability of interstellar gas. For about four and a half decades, astrophysicists have recognised the importance of the thermal instablity for the formation of clouds in the interstellar medium. Even in the past several years, many papers have concerned the role of the thermal instability in the production of molecular clouds. About three and a half decades ago, astrophysicists investigating radiative shocks noticed that for many cooling laws such shocks are unstable.…
Similar directions are obtained for the local interstellar magnetic field (ISMF) by comparing diverse data and models that sample five orders of magnetic in spatial scales. These data include the ribbon of energetic neutral atoms discovered by the Interstellar Boundary Explorer, heliosphere models, the linear polarization of light from nearby stars, the Loop I ISMF, and pulsars that are within 100--300 pc. Together these data suggest that the local ISMF direction is correlated over scales of about 100 pc, such as would be expected for the interarm region of the galaxy. The heliosphere tail-in …
Research in many areas of modern physics and astrophysics such as, e.g., indirect searches for dark matter (DM), particle acceleration in SNR shocks, and the spectrum and origin of extragalactic gamma-ray background, rely heavily on studies of cosmic rays (CRs) and associated diffuse emissions. New or improved instrumentation to explore these open issues is ready or under development. A fleet of ground-based, balloon-borne, and spacecraft instruments measures many CR species, gamma rays, radio, and synchrotron emission. Exploiting the data collected by the scientific missions to the fullest re…
Energetic gamma rays (GeV to TeV photon energy) have been detected toward several supernova remnants (SNR) that are associated with molecular clouds. If the gamma rays are produced mainly by hadronic processes rather than leptonic processes like bremsstrahlung, then the flux of energetic cosmic ray nuclei (>1 GeV) required to produce the gamma rays can be inferred at the site where the particles are accelerated in SNR shocks. It is of great interest to understand the acceleration of the cosmic rays of lower energy (<1 GeV) that accompany the energetic component. These particles of lower energy…
Dark gas in the interstellar medium (ISM) is believed to not be detectable either in CO or Hi radio emission, but it is detected by other means including gamma-rays, dust emission and extinction traced outside the Galactic plane at |b|>5 degree. In these analyses, the 21-cm HI emission is usually assumed to be completely optically thin. We have reanalyzed the HI emission from the whole sky at |b|>15 degree by considering temperature stratification in the ISM inferred from the Planck/IRAS analysis of the dust properties. The results indicate that the HI emission is saturated with an optical dep…
The bulk propagation speed of GeV-energy cosmic rays is limited by frequent scattering off hydromagnetic waves. Most galaxy evolution simulations that account for this confinement assume the gas is fully ionized and cosmic rays are well-coupled to Alfvén waves; however, multiphase density inhomogeneities, frequently under-resolved in galaxy evolution simulations, induce cosmic ray collisions and ionization-dependent transport driven by cosmic ray decoupling and elevated streaming speeds in partially neutral gas. How do cosmic rays navigate and influence such a medium, and can we constrain this…
Heating of whole interstellar dust grains by cosmic-ray (CR) particles affects the gas-grain chemistry in molecular clouds by promoting molecule desorption, diffusion, and chemical reactions on grain surfaces. The frequency of such heating $f_T$, s$^{-1}$, determines how often a certain temperature $T_{\rm CR}$, K, is reached for grains hit by CR particles. This study aims to provide astrochemists with comprehensive and updated dataset on the CR-induced whole-grain heating. We present calculations of $f_T$ and $T_{\rm CR}$ spectra for bare olivine grains with radius $a$ of 0.05; 0.1; 0.2 $μ$m,…
30 Doradus C is a superbubble which emits the brightest nonthermal X- and TeV gamma-rays in the Local Group. In order to explore detailed connection between the high energy radiation and the interstellar medium, we have carried out new CO and HI observations using the Atacama Large Millimeter$/$Submillimeter Array (ALMA), Atacama Submillimeter Telescope Experiment, and the Australia Telescope Compact Array with resolutions of up to 3 pc. The ALMA data of $^{12}$CO($J$ = 1-0) emission revealed 23 molecular clouds with the typical diameters of $\sim$6-12 pc and masses of $\sim$600-10000 $M_{\odo…
Frequent supernova explosions in compact starburst regions are a main shaper of these regions' interstellar media (ISM). In most starbursts, the supernova remnants blast open a hot phase that fills the regions and launches a superwind. Denser starbursts are too overpressured for hot wind formation, but supernovae still stir up the ISM. I argue that supernovae power ubiquitous turbulence through each of the starburst ISM phases, including the hot wind, and that a fluctuation dynamo amplifies magnetic fields until they are in equipartition with the turbulence. Supernovae can drive turbulence wit…
We report a Fermi-LAT $γ$-ray analysis for the Chamaeleon molecular-cloud complex using a total column density (NH) model based on the dust optical depth at 353 GHz ($τ_{353}$) with the Planck thermal dust emission model. Gamma rays with energy from 250 MeV to 100 GeV are fitted with the NH model as a function of $τ_{353}$, NH $\propto$ $τ_{353}^{1/α}$ ($α$ $\geq$ 1.0), to explicitly take into account a possible nonlinear $τ_{353}$/NH ratio. We found that a nonlinear relation, $α$$\sim$1.4, gives the best fit to the $γ$-ray data. This nonlinear relation may indicate dust evolution effects acro…
Radioactive components of the interstellar medium provide an entirely-different and new aspect to the studies of the interstellar medium. Injected from sources of nucleosynthesis, unstable nuclei decay along their trajectories. Measurements can occur through characteristic gamma rays that are emitted with the decay, or in cosmic material samples through abundances of parent and daughter isotopes as they change with decay. The dynamics and material flows within interstellar medium are thus accessible to measurement, making use of the intrinsic clock that radioactive decay provides. We describe …
Continuum gamma-ray emission produced by interactions of cosmic rays with interstellar matter and radiation fields is a probe of non-thermal particle populations in galaxies. After decades of continuous improvements in experimental techniques and an ever-increasing sky and energy coverage, gamma-ray observations reveal in unprecedented detail the properties of galactic cosmic rays. A variety of scales and environments are now accessible to us, from the local interstellar medium near the Sun and the vicinity of cosmic-ray accelerators, out to the Milky Way at large and beyond, with a growing nu…
Context: Cosmic rays are present in almost all phases of the ISM. PAHs and cosmic rays represent an abundant and ubiquitous component of the interstellar medium. However, the interaction between them has never before been fully investigated. Aims: To study the effects of cosmic ray ion (H, He, CNO and Fe-Co-Ni) and electron bombardment of PAHs in galactic and extragalactic environments. Methods: We calculate the nuclear and electronic interactions for collisions between PAHs and cosmic ray ions and electrons with energies between 5 MeV/nucleon and 10 GeV, above the threshold for carbon atom lo…
Cosmic rays (CRs) are thought to play a dynamically important role in several key aspects of galaxy evolution, including the structure of the interstellar medium, the formation of galactic winds, and the non-thermal pressure support of halos. We introduce a numerical model solving for the CR streaming instability and acceleration of CRs at shocks with a fluid approach in the adaptive mesh refinement code ramses. CR streaming is solved with a diffusion approach and its anisotropic nature is naturally captured. We introduce a shock finder for the ramses code that automatically detects shock disc…
Shocks are ubiquitous in the interstellar medium of galaxies, where they contribute to the energetic balance and to the cycle of matter, and where they are thought to be the primary sites for cosmic rays acceleration. Most of the time: in jets and outflows, supernova remnants, or colliding flows, they are linked with star formation. The study of shocks is hence a powerful tool to probe the evolution of the interstellar medium and to better understand star formation. To these aims, the most precise observations must be compared with the most precise models of shocks. The SOFIA/GREAT instrument …
