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Nick Indriolo - One of the best experts on this subject based on the ideXlab platform.
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the central 300 pc of the galaxy probed by infrared spectra of h _3 and co part i predominance of warm and diffuse gas and high h _2 Ionization Rate
arXiv: High Energy Astrophysical Phenomena, 2019Co-Authors: T Oka, T R Geballe, Tomonori Usuda, M Goto, J Mccall, Nick IndrioloAbstract:The molecular gas in the Central Molecular Zone (CMZ) of the Galaxy has been studied using infrared absorption spectra of H$_3^+$ lines at 3.5-4.0 $\mu$m and CO lines near 2.34 $\mu$m. In addition to the previously reported spectra of these lines toward 8 stars located within 30 pc of Sgr A$^\ast$, there are now spectra toward $\sim$30 bright stars located from 140 pc west to 120 pc east of Sgr A$^\ast$. The spectra show the presence of warm ($T\sim 200$ K) and diffuse ($n < 100 $cm$^{-3}$) gas with $N$(H$_3^+$) $\sim 3 \times 10^{15} $cm$^{-2}$ on majority of sightlines. Instead of our previous analysis in which only electrons from photoIonization of carbon atoms were considered, we have developed a simple model calculation in which the cosmic ray Ionization of H$_2$ and H are also taken into account. We conclude: (1) Warm and diffuse gas dominates the volume of the CMZ. The volume filling factor of dense gas must be much less than 0.1 and the CMZ is not as opaque as previously considered. The X-ray emitting ultra-hot 10$^8 $K plasma, which some thought to dominate the CMZ, does not exist over extended regions. (2) The cosmic ray Ionization Rate is $\zeta \sim 2 \times 10^{-14} $s$^{-1}$, higher than in Galactic dense clouds and diffuse clouds by factors of $\sim$1000 and $\sim$100, respectively. If the equipartition law stands, this suggests a pervading magnetic field on the order of $\sim$100 $\mu$G.
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herschel survey of galactic oh h2o and h3o probing the molecular hydrogen fraction and cosmic ray Ionization Rate
The Astrophysical Journal, 2015Co-Authors: Nick Indriolo, David A Neufeld, M Gerin, J H Black, K M Menten, P Schilke, A O Benz, B Winkel, E Chambers, S BrudererAbstract:In diffuse interstellar clouds the chemistry that leads to the formation of the oxygen-bearing ions OH+, H2O+, and H3O+ begins with the Ionization of atomic hydrogen by cosmic rays, and continues through subsequent hydrogen abstraction reactions involving H2. Given these reaction pathways, the observed abundances of these molecules are useful in constraining both the total cosmic-ray Ionization Rate of atomic hydrogen (ζH) and molecular hydrogen fraction (f_H_2). We present observations targeting transitions of OH+, H2O+, and H3O+ made with the Herschel Space Observatory along 20 Galactic sight lines toward bright submillimeter continuum sources. Both OH+ and H2O+ are detected in absorption in multiple velocity components along every sight line, but H3O+ is only detected along 7 sight lines. From the molecular abundances we compute f_H_2 in multiple distinct components along each line of sight, and find a Gaussian distribution with mean and standard deviation 0.042 ± 0.018. This confirms previous findings that OH+ and H2O+ primarily reside in gas with low H2 fractions. We also infer ζH throughout our sample, and find a lognormal distribution with mean log (ζH) = –15.75 (ζH = 1.78 × 10–16 s–1) and standard deviation 0.29 for gas within the Galactic disk, but outside of the Galactic center. This is in good agreement with the mean and distribution of cosmic-ray Ionization Rates previously inferred from H_3^+ observations. Ionization Rates in the Galactic center tend to be 10-100 times larger than found in the Galactic disk, also in accord with prior studies.
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herschel survey of galactic oh h2o and h3o probing the molecular hydrogen fraction and cosmic ray Ionization Rate
arXiv: Astrophysics of Galaxies, 2014Co-Authors: Nick Indriolo, David A Neufeld, M Gerin, J H Black, K M Menten, P Schilke, A O Benz, B Winkel, E Chambers, S BrudererAbstract:In diffuse interstellar clouds the chemistry that leads to the formation of the oxygen bearing ions OH+, H2O+, and H3O+ begins with the Ionization of atomic hydrogen by cosmic rays, and continues through subsequent hydrogen abstraction reactions involving H2. Given these reaction pathways, the observed abundances of these molecules are useful in constraining both the total cosmic-ray Ionization Rate of atomic hydrogen (zeta_H) and molecular hydrogen fraction, f(H2). We present observations targeting transitions of OH+, H2O+, and H3O+ made with the Herschel Space Observatory along 20 Galactic sight lines toward bright submillimeter continuum sources. Both OH+ and H2O+ are detected in absorption in multiple velocity components along every sight line, but H3O+ is only detected along 7 sight lines. From the molecular abundances we compute f(H2) in multiple distinct components along each line of sight, and find a Gaussian distribution with mean and standard deviation 0.042+-0.018. This confirms previous findings that OH+ and H2O+ primarily reside in gas with low H2 fractions. We also infer zeta_H throughout our sample, and find a log-normal distribution with mean log(zeta_H)=-15.75, (zeta_H=1.78x10^-16 s^-1), and standard deviation 0.29 for gas within the Galactic disk, but outside of the Galactic center. This is in good agreement with the mean and distribution of cosmic-ray Ionization Rates previously inferred from H3+ observations. Ionization Rates in the Galactic center tend to be 10--100 times larger than found in the Galactic disk, also in accord with prior studies.
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h3 spectroscopy and the Ionization Rate of molecular hydrogen in the central few parsecs of the galaxy
Journal of Physical Chemistry A, 2013Co-Authors: Miwa Goto, Nick Indriolo, T R Geballe, Tomonori UsudaAbstract:We report observations and analysis of infrared spectra of H3(+) and CO lines in the Galactic center, within a few parsecs of the central black hole, Sgr A*. We find a cosmic ray Ionization Rate typically an order of magnitude higher than outside the Galactic center. Notwithstanding, the elevated cosmic ray Ionization Rate is 4 orders of magnitude too short to match the proton energy spectrum, as inferred from the recent discovery of the TeV γ-ray source in the vicinity of Sgr A*.
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chemical analysis of a diffuse cloud along a line of sight toward w51 molecular fraction and cosmic ray Ionization Rate
The Astrophysical Journal, 2012Co-Authors: Nick Indriolo, T R Geballe, David A Neufeld, M Gerin, J H Black, K M Menten, J R GoicoecheaAbstract:Absorption lines from the molecules OH+, H2O+, and H-3(+) have been observed in a diffuse molecular cloud along a line of sight near W51 IRS2. We present the first chemical analysis that combines the information provided by all three of these species. Together, OH+ and H2O+ are used to determine the molecular hydrogen fraction in the outskirts of the observed cloud, as well as the cosmic-ray Ionization Rate of atomic hydrogen. H-3(+) is used to infer the cosmic-ray Ionization Rate of H-2 in the molecular interior of the cloud, which we find to be zeta(2) = (4.8 +/- 3.4) x 10(-16) s(-1). Combining the results from all three species we find an efficiency factor-defined as the ratio of the formation Rate of OH+ to the cosmic-ray Ionization Rate of H-of epsilon = 0.07+/-0.04, much lower than predicted by chemical models. This is an important step in the future use of OH+ and H2O+ on their own as tracers of the cosmic-ray Ionization Rate.
Benjamin J Mccall - One of the best experts on this subject based on the ideXlab platform.
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investigating the cosmic ray Ionization Rate in the galactic diffuse interstellar medium through observations of h 3
The Astrophysical Journal, 2012Co-Authors: Nick Indriolo, Benjamin J MccallAbstract:Observations of H{sup +}{sub 3} in the Galactic diffuse interstellar medium have led to various surprising results, including the conclusion that the cosmic-ray Ionization Rate ({zeta}{sub 2}) is about one order of magnitude larger than previously thought. The present survey expands the sample of diffuse cloud sight lines with H{sup +}{sub 3} observations to 50, with detections in 21 of those. Ionization Rates inferred from these observations are in the range (1.7 {+-} 1.3) Multiplication-Sign 10{sup -16} s{sup -1} < {zeta}{sub 2} < (10.6 {+-} 8.2) Multiplication-Sign 10{sup -16} s{sup -1} with a mean value of {zeta}{sub 2} = (3.5{sup +5.3}{sub -3.0}) Multiplication-Sign 10{sup -16} s{sup -1}. Upper limits (3{sigma}) derived from non-detections of H{sup +}{sub 3} are as low as {zeta}{sub 2} < 0.4 Multiplication-Sign 10{sup -16} s{sup -1}. These low upper limits, in combination with the wide range of inferred cosmic-ray Ionization Rates, indicate variations in {zeta}{sub 2} between different diffuse cloud sight lines. A study of {zeta}{sub 2} versus N{sub H} (total hydrogen column density) shows that the two parameters are not correlated for diffuse molecular cloud sight lines, but that the Ionization Rate decreases when N{sub H} increases to values typical of dense molecular clouds. Bothmore » the difference in Ionization Rates between diffuse and dense clouds and the variation of {zeta}{sub 2} among diffuse cloud sight lines are likely the result of particle propagation effects. The lower Ionization Rate in dense clouds is due to the inability of low-energy (few MeV) protons to penetRate such regions, while the Ionization Rate in diffuse clouds is controlled by the proximity of the observed cloud to a site of particle acceleration.« less
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investigating the cosmic ray Ionization Rate in the galactic diffuse interstellar medium through observations of h3
arXiv: Astrophysics of Galaxies, 2011Co-Authors: Nick Indriolo, Benjamin J MccallAbstract:Observations of H3+ in the Galactic diffuse interstellar medium (ISM) have led to various surprising results, including the conclusion that the cosmic-ray Ionization Rate (zeta_2) is about 1 order of magnitude larger than previously thought. The present survey expands the sample of diffuse cloud sight lines with H3+ observations to 50, with detections in 21 of those. Ionization Rates inferred from these observations are in the range (1.7+-1.3)x10^-16 s^-1
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interstellar metastable helium absorption as a probe of the cosmic ray Ionization Rate
The Astrophysical Journal, 2009Co-Authors: Nick Indriolo, L M Hobbs, Kenneth H Hinkle, Benjamin J MccallAbstract:The Ionization Rate of interstellar material by cosmic rays has been a major source of controversy, with different estimates varying by three orders of magnitude. Observational constraints of this Rate have all depended on analyzing the chemistry of various molecules that are produced following cosmic-ray Ionization, and in many cases these analyses contain significant uncertainties. Even in the simplest case (H+ 3), the derived Ionization Rate depends on an (uncertain) estimate of the absorption path length. In this paper, we examine the feasibility of inferring the cosmic-ray Ionization Rate using the 10830 A absorption line of metastable helium. Observations through the diffuse clouds toward HD 183143 are presented, but yield only an upper limit on the metastable helium column density. A thorough investigation of He+ chemistry reveals that only a small fraction of He+ will recombine into the triplet state and populate the metastable level. In addition, excitation to the triplet manifold of helium by secondary electrons must be accounted for as it is the dominant mechanism which produces He* in some environments. Incorporating these various formation and destruction pathways, we derive new equations for the steady state abundance of metastable helium. Using these equations in concert with our observations, we find ζHe < 1.2 × 10–15 s–1, an upper limit about 5 times larger than the Ionization Rate previously inferred for this sight line using H+ 3. While observations of interstellar He* are extremely difficult at present, and the background chemistry is not nearly as simple as previously thought, potential future observations of metastable helium would provide an independent check on the cosmic-ray Ionization Rate derived from H+ 3 in diffuse molecular clouds, and, perhaps more importantly, allow the first direct measurements of the Ionization Rate in diffuse atomic clouds.
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interstellar metastable helium absorption as a probe of the cosmic ray Ionization Rate
arXiv: Solar and Stellar Astrophysics, 2009Co-Authors: Nick Indriolo, L M Hobbs, Kenneth H Hinkle, Benjamin J MccallAbstract:The Ionization Rate of interstellar material by cosmic rays has been a major source of controversy, with different estimates varying by three orders of magnitude. Observational constraints of this Rate have all depended on analyzing the chemistry of various molecules that are produced following cosmic-ray Ionization, and in many cases these analyses contain significant uncertainties. Even in the simplest case (H3+) the derived Ionization Rate depends on an (uncertain) estimate of the absorption path length. In this paper we examine the feasibility of inferring the cosmic-ray Ionization Rate using the 10830 A absorption line of metastable helium. Observations through the diffuse clouds toward HD 183143 are presented, but yield only an upper limit on the metastable helium column density. A thorough investigation of He+ chemistry reveals that only a small fraction of He+ will recombine into the triplet state and populate the metastable level. In addition, excitation to the triplet manifold of helium by secondary electrons must be accounted for as it is the dominant mechanism which produces He* in some environments. Incorporating these various formation and destruction pathways, we derive new equations for the steady state abundance of metastable helium. Using these equations in concert with our observations, we find zeta_He < 1.2*10^-15 s^-1, an upper limit about 5 times larger than the Ionization Rate previously inferred for this sight line using H3+. While observations of interstellar He* are extremely difficult at present...
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the implications of a high cosmic ray Ionization Rate in diffuse interstellar clouds
arXiv: High Energy Astrophysical Phenomena, 2009Co-Authors: Nick Indriolo, Brian D Fields, Benjamin J MccallAbstract:Diffuse interstellar clouds show large abundances of H_3^+ which can be maintained only by a high Ionization Rate of H_2. Cosmic rays are the dominant Ionization mechanism in this environment, so the large Ionization Rate implies a high cosmic-ray flux, and a large amount of energy residing in cosmic rays. In this paper we find that the standard propagated cosmic-ray spectrum predicts an Ionization Rate much lower than that inferred from H_3^+. Low-energy (~10 MeV) cosmic rays are the most efficient at ionizing hydrogen, but cannot be directly detected; consequently, an otherwise unobservable enhancement of the low-energy cosmic-ray flux offers a plausible explanation for the H_3^+ results. Beyond Ionization, cosmic rays also interact with the interstellar medium by spalling atomic nuclei and exciting atomic nuclear states. These processes produce the light elements Li, Be, and B, as well as gamma-ray lines. To test the consequences of an enhanced low-energy cosmic-ray flux, we adopt two physically-motivated cosmic-ray spectra which by construction reproduce the Ionization Rate inferred in diffuse clouds, and investigate the implications of these spectra on dense cloud Ionization Rates, light element abundances, gamma-ray fluxes, and energetics. One spectrum proposed here provides an explanation for the high Ionization Rate seen in diffuse clouds while still appearing to be broadly consistent with other observables, but the shape of this spectrum suggests that supernovae remnants may not be the predominant accelerators of low-energy cosmic rays.
Toru Morishita - One of the best experts on this subject based on the ideXlab platform.
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weak field asymptotic theory of tunneling Ionization in many electron atomic and molecular systems
Physical Review A, 2014Co-Authors: Lars Bojer Madsen, Oleg I Tolstikhin, Toru MorishitaAbstract:The weak-field asymptotic theory of tunneling Ionization in an external static uniform electric field [Tolstikhin et al., Phys. Rev. A 84, 053423 (2011)] is extended to many-electron atomic and molecular systems treated in the frozen-nuclei approximation. The leading-order term in the asymptotic expansion of the Ionization Rate $\ensuremath{\Gamma}$ in the value of the field $F$ for $F\ensuremath{\rightarrow}0$ is obtained. The resulting formulas express $\ensuremath{\Gamma}$ in terms of properties of the unperturbed system. The most essential difference from the one-electron case, through which the many-electron character of the present theory reveals itself, is that the structure factor for a given Ionization channel, defining the dependence of the Ionization Rate into this channel on the orientation of the system with respect to the field, is determined by the corresponding Dyson orbital. The theory is illustRated by calculations for several few-electron systems. The asymptotic results are compared with accuRate fully correlated calculations of tunneling Ionization Rates available in the literature.
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application of the weak field asymptotic theory to the analysis of tunneling Ionization of linear molecules
Physical Review A, 2012Co-Authors: Lars Bojer Madsen, Oleg I Tolstikhin, Toru MorishitaAbstract:The recently developed weak-field asymptotic theory [Phys. Rev. A 84, 053423 (2011)] is applied to the analysis of tunneling Ionization of a molecular ion (H${}_{2}^{+}$), several homonuclear (H${}_{2}$, N${}_{2}$, O${}_{2}$) and heteronuclear (CO, HF) diatomic molecules, and a linear triatomic molecule (CO${}_{2}$) in a static electric field. The dependence of the Ionization Rate on the angle between the molecular axis and the field is determined by a structure factor for the highest occupied molecular orbital. This factor is calculated using a virtually exact discrete variable representation wave function for H${}_{2}^{+}$, very accuRate Hartree-Fock wave functions for the diatomics, and a Hartree-Fock quantum chemistry wave function for CO${}_{2}$. The structure factors are expanded in terms of standard functions and the associated structure coefficients, allowing the determination of the Ionization Rate for any orientation of the molecule with respect to the field, are tabulated. Our results, which are exact in the weak-field limit for H${}_{2}^{+}$ and, in addition, under the Hartree-Fock approximation for the diatomics, are compared with results from the recent literature.
Oleg I Tolstikhin - One of the best experts on this subject based on the ideXlab platform.
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weak field asymptotic theory of tunneling Ionization in many electron atomic and molecular systems
Physical Review A, 2014Co-Authors: Lars Bojer Madsen, Oleg I Tolstikhin, Toru MorishitaAbstract:The weak-field asymptotic theory of tunneling Ionization in an external static uniform electric field [Tolstikhin et al., Phys. Rev. A 84, 053423 (2011)] is extended to many-electron atomic and molecular systems treated in the frozen-nuclei approximation. The leading-order term in the asymptotic expansion of the Ionization Rate $\ensuremath{\Gamma}$ in the value of the field $F$ for $F\ensuremath{\rightarrow}0$ is obtained. The resulting formulas express $\ensuremath{\Gamma}$ in terms of properties of the unperturbed system. The most essential difference from the one-electron case, through which the many-electron character of the present theory reveals itself, is that the structure factor for a given Ionization channel, defining the dependence of the Ionization Rate into this channel on the orientation of the system with respect to the field, is determined by the corresponding Dyson orbital. The theory is illustRated by calculations for several few-electron systems. The asymptotic results are compared with accuRate fully correlated calculations of tunneling Ionization Rates available in the literature.
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application of the weak field asymptotic theory to the analysis of tunneling Ionization of linear molecules
Physical Review A, 2012Co-Authors: Lars Bojer Madsen, Oleg I Tolstikhin, Toru MorishitaAbstract:The recently developed weak-field asymptotic theory [Phys. Rev. A 84, 053423 (2011)] is applied to the analysis of tunneling Ionization of a molecular ion (H${}_{2}^{+}$), several homonuclear (H${}_{2}$, N${}_{2}$, O${}_{2}$) and heteronuclear (CO, HF) diatomic molecules, and a linear triatomic molecule (CO${}_{2}$) in a static electric field. The dependence of the Ionization Rate on the angle between the molecular axis and the field is determined by a structure factor for the highest occupied molecular orbital. This factor is calculated using a virtually exact discrete variable representation wave function for H${}_{2}^{+}$, very accuRate Hartree-Fock wave functions for the diatomics, and a Hartree-Fock quantum chemistry wave function for CO${}_{2}$. The structure factors are expanded in terms of standard functions and the associated structure coefficients, allowing the determination of the Ionization Rate for any orientation of the molecule with respect to the field, are tabulated. Our results, which are exact in the weak-field limit for H${}_{2}^{+}$ and, in addition, under the Hartree-Fock approximation for the diatomics, are compared with results from the recent literature.
Lars Bojer Madsen - One of the best experts on this subject based on the ideXlab platform.
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weak field asymptotic theory of tunneling Ionization in many electron atomic and molecular systems
Physical Review A, 2014Co-Authors: Lars Bojer Madsen, Oleg I Tolstikhin, Toru MorishitaAbstract:The weak-field asymptotic theory of tunneling Ionization in an external static uniform electric field [Tolstikhin et al., Phys. Rev. A 84, 053423 (2011)] is extended to many-electron atomic and molecular systems treated in the frozen-nuclei approximation. The leading-order term in the asymptotic expansion of the Ionization Rate $\ensuremath{\Gamma}$ in the value of the field $F$ for $F\ensuremath{\rightarrow}0$ is obtained. The resulting formulas express $\ensuremath{\Gamma}$ in terms of properties of the unperturbed system. The most essential difference from the one-electron case, through which the many-electron character of the present theory reveals itself, is that the structure factor for a given Ionization channel, defining the dependence of the Ionization Rate into this channel on the orientation of the system with respect to the field, is determined by the corresponding Dyson orbital. The theory is illustRated by calculations for several few-electron systems. The asymptotic results are compared with accuRate fully correlated calculations of tunneling Ionization Rates available in the literature.
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application of the weak field asymptotic theory to the analysis of tunneling Ionization of linear molecules
Physical Review A, 2012Co-Authors: Lars Bojer Madsen, Oleg I Tolstikhin, Toru MorishitaAbstract:The recently developed weak-field asymptotic theory [Phys. Rev. A 84, 053423 (2011)] is applied to the analysis of tunneling Ionization of a molecular ion (H${}_{2}^{+}$), several homonuclear (H${}_{2}$, N${}_{2}$, O${}_{2}$) and heteronuclear (CO, HF) diatomic molecules, and a linear triatomic molecule (CO${}_{2}$) in a static electric field. The dependence of the Ionization Rate on the angle between the molecular axis and the field is determined by a structure factor for the highest occupied molecular orbital. This factor is calculated using a virtually exact discrete variable representation wave function for H${}_{2}^{+}$, very accuRate Hartree-Fock wave functions for the diatomics, and a Hartree-Fock quantum chemistry wave function for CO${}_{2}$. The structure factors are expanded in terms of standard functions and the associated structure coefficients, allowing the determination of the Ionization Rate for any orientation of the molecule with respect to the field, are tabulated. Our results, which are exact in the weak-field limit for H${}_{2}^{+}$ and, in addition, under the Hartree-Fock approximation for the diatomics, are compared with results from the recent literature.
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strong field Ionization of atoms and molecules the two term saddle point method
Physical Review A, 2006Co-Authors: Thomas Kim Kjeldsen, Lars Bojer MadsenAbstract:We derive an analytical formula for the Ionization Rate of neutral atoms and molecules in a strong monochromatic field. Our model is based on the strong-field approximation with transition amplitudes calculated by an extended saddle-point method. We show that the present two-term saddle-point method reproduces even complicated structures in angular resolved photoelectron spectra.
