scholarly journals Exploring the central molecular zone of the Galaxy using spectroscopy of H 3 + and CO

2012 ◽  
Vol 370 (1978) ◽  
pp. 5151-5161 ◽  
Author(s):  
T. R. Geballe
Keyword(s):  
Large Fraction ◽  
Level Structure ◽  
Cosmic Ray ◽  
Ionization Rate ◽  
Radiative Properties ◽  
Molecular Gas ◽  
Interstellar Gas ◽  
Energy Level Structure ◽  
Wide Range ◽  
The Galaxy

The central 400 parsecs of the Milky Way, a region known as the central molecular zone (CMZ), contains interstellar gas in a wide range of physical environments, from ultra-hot, rarified and highly ionized to warm, dense and molecular. The combination of infrared spectroscopy of and CO is a powerful way to determine the basic properties of molecular interstellar gas, because the abundance ratio of to CO in ‘dense’ clouds is quite different from that in ‘diffuse’ clouds. Moreover, the energy-level structure and the radiative properties of combined with the unusually warm temperatures of molecular gas in the CMZ make a unique probe of the physical conditions there. This paper describes how, using infrared absorption spectroscopy of and CO, it has been discovered that a large fraction of the volume of the CMZ is filled with warm, diffuse and partially molecular gas moving at speeds of up to approximately 200 km s −1 and that the mean cosmic ray ionization rate in the CMZ exceeds by roughly an order of magnitude values found in diffuse molecular clouds elsewhere in the Galaxy.

Evidence for Large Scale Cosmic Ray Electron Gradients in the Galaxy

1976 ◽  
Vol 3 (1) ◽  
pp. 1-6 ◽  
Author(s):  
W. R. Webber
Keyword(s):  
Large Scale ◽  
Spiral Structure ◽  
Cosmic Ray ◽  
Point Sources ◽  
Interstellar Matter ◽  
Interstellar Gas ◽  
The Galaxy ◽  
Ray Density ◽  
Γ Rays ◽  
Γ Ray

In recent years observations of γ-ray emission from the disk of the galaxy have provided a new opportunity for research into the structure of the spiral arms of our own galaxy. In Figure 1 we show a map of the structure of the disk of the galaxy as observed for γ-rays of energy > 100 MeV by the SAS-2 satellite (Fichtel et al. 1975). The angular resolution of these measurements is ~ 3°, and besides two point sources at l = 190° and 265° several features related to the spiral structure of the galaxy are evident in the data. Most of these γ-rays are believed to arise from the decay of π° mesons produced by the nuclear interactions of cosmic rays (mostly protons) with the ambient interstellar gas. As a result, the γ-ray fluxes represent a measure of the line of sight integral of the product of the cosmic ray density NCR and the interstellar matter density N1

scholarly journals Hydride spectroscopy of the diffuse interstellar medium: new clues on the gas fraction in molecular form and cosmic ray ionization rate in relation to H 3 +

2012 ◽  
Vol 370 (1978) ◽  
pp. 5174-5185 ◽  
Author(s):  
M. Gerin ◽  
F. Levrier ◽  
E. Falgarone ◽  
B. Godard ◽  
P. Hennebelle ◽  
...  
Keyword(s):  
Molecular Form ◽  
Chemical Properties ◽  
Cosmic Ray ◽  
Building Blocks ◽  
Ionization Rate ◽  
Spectral Lines ◽  
Interstellar Gas ◽  
Interstellar Molecules ◽  
Star Forming ◽  
Star Forming Regions

The Herschel-guaranteed time key programme PRobing InterStellar Molecules with Absorption line Studies (PRISMAS) 1 is providing a survey of the interstellar hydrides containing the elements C, O, N, F and Cl. As the building blocks of interstellar molecules, hydrides provide key information on their formation pathways. They can also be used as tracers of important physical and chemical properties of the interstellar gas that are difficult to measure otherwise. This paper presents an analysis of two sight-lines investigated by the PRISMAS project, towards the star-forming regions W49N and W51. By combining the information extracted from the detected spectral lines, we present an analysis of the physical properties of the diffuse interstellar gas, including the electron abundance, the fraction of gas in molecular form, and constraints on the cosmic ray ionization rate and the gas density.

Cosmic-ray nuclei up to 10 10 eV/u in the galaxy

1975 ◽  
Vol 277 (1270) ◽  
pp. 319-348 ◽  
Keyword(s):  
Cosmic Rays ◽  
Solar System ◽  
Cross Sections ◽  
Cosmic Ray ◽  
Interstellar Space ◽  
Heavy Nuclei ◽  
Hydrogen Atoms ◽  
Interstellar Gas ◽  
The Galaxy ◽  
Ionization Cross Sections

O f the nuclear cosmic rays arriving in the vicinity of Earth from interstellar space, more than 90% have energies less than 1010 eV /u.f Some effects of their modulation (including deceleration) in the Solar System are briefly discussed. The origin of particles at energies < 107 eV/u is still obscure. They could be due to stellar explosions or to solar emissions, or perhaps to interaction of interstellar gas with the solar wind. Between 108 and 1010 eV/u, the composition appears constant to ca. 30% within the statistics of available data. Cosmic rays traverse a mean path length of 6 g/cm 2 in a medium assumed to contain nine hydrogen atoms for each helium atom. Spallation reactions occurring in this medium result in enhancement of many cosmic-ray elements that are more scarce in the general abundances by several orders of magnitude. Cosmic-ray dwell time in the Galaxy seems to be < 107 years. The source composition of cosmic rays has been derived for elements with atomic numbers 1 ≤ Z ≤ 26. A comparison with abundances in the Solar System implies that the latter is richer in hydrogen and helium by a factor of ca. 20, in N and O by ca. 5, and in C by a factor of ca.2. Possible interpretations invoke (a) nucleosynthesis of cosmic rays in certain sources, e.g. supernovae, or (b) models of selective injection that depend, e.g. on ionization potentials or ionization cross sections. Calculated isotopic abundances of arriving cosmic rays are compared with the observed values now becoming available, and found to be in general agreement. Recent progress in probing the composition and spectrum of ultra-heavy nuclei is outlined.

scholarly journals The distribution of cosmic-ray ionization rates in diffuse molecular clouds as probed by H 3 +

2012 ◽  
Vol 370 (1978) ◽  
pp. 5142-5150 ◽  
Author(s):  
Nick Indriolo
Keyword(s):  
Molecular Clouds ◽  
Cosmic Ray ◽  
Ionization Rate ◽  
Line Of Sight ◽  
Interstellar Clouds ◽  
Upper Limits ◽  
The Galaxy ◽  
Cosmic Ray Flux ◽  
Made In ◽  
Ionization Rates

Owing to its simple chemistry, H is widely regarded as the most reliable tracer of the cosmic-ray ionization rate in diffuse interstellar clouds. At present, H observations have been made in over 50 sight lines that probe the diffuse interstellar medium (ISM) throughout the Galaxy. This small survey presents the opportunity to investigate the distribution of cosmic-ray ionization rates in the ISM, as well as any correlations between the ionization rate and line-of-sight properties. Some of the highest inferred ionization rates are about 25 times larger than the lowest upper limits, suggesting variations in the underlying low-energy cosmic-ray flux across the Galaxy. Most likely, such variations are caused predominantly by the distance between an observed cloud and the nearest site of particle acceleration.

scholarly journals Arcminute-scale studies of the interstellar gas towards HESS J1804−216: Still an unidentified TeV γ-ray source

2020 ◽  
Vol 37 ◽  
Author(s):  
Kirsty Feijen ◽  
Gavin Rowell ◽  
Sabrina Einecke ◽  
Catherine Braiding ◽  
Michael G. Burton ◽  
...  
Keyword(s):  
Supernova Remnant ◽  
Galactic Plane ◽  
Cosmic Ray ◽  
Line Of Sight ◽  
Dispersion Measure ◽  
Molecular Gas ◽  
Interstellar Gas ◽  
Isotropic Diffusion ◽  
Unidentified Source ◽  
Using Data

Abstract The Galactic TeV ${\gamma}$ -ray source ${\mathrm{HESS\,J}1804{-}216}$ is currently an unidentified source. In an attempt to unveil its origin, we present here the most detailed study of interstellar gas using data from the Mopra Southern Galactic Plane CO Survey, 7- and 12-mm wavelength Mopra surveys and Southern Galactic Plane Survey of HI. Several components of atomic and molecular gas are found to overlap ${\mathrm{HESS\,J}1804{-}216}$ at various velocities along the line of sight. The CS(1-0) emission clumps confirm the presence of dense gas. Both correlation and anti-correlation between the gas and TeV ${\gamma}$ -ray emission have been identified in various gas tracers, enabling several origin scenarios for the TeV ${\gamma}$ -ray emission from ${\mathrm{HESS\,J}1804{-}216}$ . For a hadronic scenario, ${\mathrm{SNR\,G}8.7{-}0.1}$ and the progenitor supernova remnant (SNR) of ${\mathrm{PSR\,J}1803{-}2137}$ require cosmic ray (CR) enhancement factors of ${\mathord{\sim} 50}$ times the solar neighbour CR flux value to produce the TeV ${\gamma}$ -ray emission. Assuming an isotropic diffusion model, CRs from both these SNRs require a slow diffusion coefficient, as found for other TeV SNRs associated with adjacent ISM gas. The morphology of gas located at 3.8 kpc (the dispersion measure distance to ${\mathrm{PSR\,J}1803{-}2137}$ ) tends to anti-correlate with features of the TeV emission from ${\mathrm{HESS\,J}1804{-}216}$ , making the leptonic scenario possible. Both pure hadronic and pure leptonic scenarios thus remain plausible.

Pulsar scintillation as a physical tool

1992 ◽  
Vol 341 (1660) ◽  
pp. 167-176 ◽  
Keyword(s):  
Spatial Coherence ◽  
Line Of Sight ◽  
Interstellar Gas ◽  
Pulsar Emission ◽  
Pulsar Radiation ◽  
Wide Range ◽  
Random Modulation ◽  
Radio Frequency Spectrum ◽  
The Galaxy ◽  
Diffraction Patterns

The interstellar gas contains irregularities of electron density having a wide range of physical scales. Pulsar radiation propagating through this inhomogeneous medium suffers a random modulation of phase which causes the received intensity to scintillate on a variety of timescales. Observations of the radio frequency spectrum and temporal variation of scintillation give information on the form of the irregularity spectrum and the distribution of density structure across the Galaxy. The high spatial coherence of pulsar radiation leads to the formation of extremely fine-scale diffraction patterns which also provide information on the motion of sources across the line of sight and the size of pulsar emission regions. Some uses of scintillation as a means of probing the interstellar gas and elucidating the physical properties of pulsars will be discussed.

scholarly journals Planetary Nebulae and Nitrogen Enrichment in the Galaxy

1977 ◽  
Vol 45 ◽  
pp. 187-191 ◽  
Author(s):  
D.C.V. Mallik
Keyword(s):  
Planetary Nebula ◽  
Convection Zone ◽  
Large Fraction ◽  
Nitrogen Enrichment ◽  
Interstellar Gas ◽  
Helium Burning ◽  
Convective Envelope ◽  
The Galaxy ◽  
Long Time ◽  
Nitrogen Abundance

All stars in the mass interval 1-4Mʘprobably evolve through a double shell source phase before losing their entire envelopes through stellar wind and the ejection of planetary nebula shells. The remnant carbon-oxygen core rapidly evolves to a blue nucleus, illuminates the surrounding nebula for a few tens of thousands of years and finally cools off as a white dwarf (Paczynski, 1970, Harm and Schwarzschild 1975). A large fraction of the mass contained in the main-sequence stars of mass 1-4Mʘthus returns to the interstellar medium. A common feature of the double shell source (DSS) evolution of stars is the occurrence of He shell flashes. Evolutionary studies by Schwarzschild and Harm (1967), Iben (1975) and others show that the flash-driven convection zone carries helium burning products towards the hydrogen-rich layers. The consequences of mixing between the outer convective envelope and the intershell region have received a great deal of attention in recent years particularly in connection with the interpretation of carbon stars. If a deep temporary convection zone exists extending from the surface of the star to a point near the helium burning shell and mixing is allowed to take place for sufficiently long time Sackmann, Smith, and Despain (1974) found that the flash-produced12C underwent further ON0 processing enriching the surface of the star in12N. Iben (1976) has also speculated on the possibility of surface enrichment of14N during the DSS evolution of intermediate-mass stars. The subsequent loss of this envelope as a planetary nebula shell can thus cause nitrogen enrichment of the interstellar gas. In the present work we have evaluated the extent of this enrichment and have also derived the gradient of nitrogen abundance in the disc of the Galaxy based on the simple model of galactic evolution due to Talbot and Arnett (1973, hereinafter TA).

scholarly journals Photodissociation region diagnostics across galactic environments

2021 ◽  
Vol 502 (2) ◽  
pp. 2701-2732
Author(s):  
Thomas G Bisbas ◽  
Jonathan C Tan ◽  
Kei E I Tanaka
Keyword(s):  
Three Dimensional ◽  
Cosmic Ray ◽  
Ionization Rate ◽  
Energy Distributions ◽  
Line Energy ◽  
Conversion Factors ◽  
Line Intensities ◽  
Wide Range ◽  
Photodissociation Region ◽  
Ionization Rates

ABSTRACT We present three-dimensional astrochemical simulations and synthetic observations of magnetized, turbulent, self-gravitating molecular clouds. We explore various galactic interstellar medium environments, including cosmic ray ionization rates in the range of ζCR = 10−17–$10^{-14}\, {\rm s}^{-1}$, far-UV intensities in the range of G0 = 1–103 and metallicities in the range of Z = 0.1–$2\, {\rm Z}_{\odot }$. The simulations also probe a range of densities and levels of turbulence, including cases where the gas has undergone recent compression due to cloud–cloud collisions. We examine: (i) the column densities of carbon species across the cycle of C ii, C i, and CO, along with O i, in relation to the H i-to-H2 transition; (ii) the velocity-integrated emission of [C ii] 158 μm, [13C ii] 158 μm, [C i] 609 μm and 370 μm, [O i] 63 μm and 146 μm, and of the first ten 12CO rotational transitions; (iii) the corresponding Spectral Line Energy Distributions; (iv) the usage of [C ii] and [O i] 63 μm to describe the dynamical state of the clouds; (v) the behaviour of the most commonly used ratios between transitions of CO and [C i]; and (vi) the conversion factors for using CO and C i as H2-gas tracers. We find that enhanced cosmic ray energy densities enhance all aforementioned line intensities. At low metallicities, the emission of [C ii] is well connected with the H2 column, making it a promising new H2 tracer in metal-poor environments. The conversion factors of XCO and XC i depend on metallicity and the cosmic ray ionization rate, but not on FUV intensity. In the era of ALMA, SOFIA, and the forthcoming CCAT-prime telescope, our results can be used to understand better the behaviour of systems in a wide range of galactic and extragalactic environments.

scholarly journals Cosmic-ray evidence for a halo

1979 ◽  
Vol 84 ◽  
pp. 485-490
Author(s):  
V. L. Ginzburg
Keyword(s):  
Synchrotron Radiation ◽  
Energy Density ◽  
Cosmic Rays ◽  
Solar System ◽  
Thermal Energy ◽  
Cosmic Ray ◽  
Gas Composition ◽  
Electron Component ◽  
Interstellar Gas ◽  
The Galaxy

Cosmic rays were discovered in 1912, but it was only about forty years later that they were found to play an important role in astronomy. Firstly, cosmic rays (including the electron component) are an important source of astronomical information, namely the cosmic synchrotron radiation. Secondly, cosmic rays are essential as energetic and dynamical factors in the galaxy and also as a source of heating and transformation of the interstellar gas composition. Suffice it to remember, for example, that near the solar system the cosmic ray energy density is about the same as the thermal energy of the interstellar gas, and the cosmic ray pressure is likewise about the same as the interstellar gas pressure. Thus, there is every reason to believe that galaxies do not consist of stars and gas only, but of cosmic rays as well.

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