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Michael T. Murphy - One of the best experts on this subject based on the ideXlab platform.
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a cold component and the Complex Velocity structure of dla1331 170
Monthly Notices of the Royal Astronomical Society, 2011Co-Authors: Robert F. Carswell, Regina A. Jorgenson, Arthur M. Wolfe, Michael T. MurphyAbstract:We examine the Velocity structure in the gas associated with H I in the damped Lyα absorption system at redshift z = 1.7764 towards the QSO 1331 + 170 using Arecibo H i 21-cm data, optical spectra from the Keck High Resolution Echelle Spectrograph (HIRES) and European Southern Observatory (ESO) Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES), and a previously published Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) ultraviolet spectrum. From the optical data we find at least two, and possibly three, components showing C I lines. One of these has very narrow lines with Doppler parameter b = 0.55 km s ―1 , corresponding to a kinetic temperature of 220 K if the broadening is thermal and with a 2σ upper limit of 480 K. We re-examine the H 2 analysis undertaken by Cui et al. using the neutral carbon Velocity structure, and find a model which is, unlike theirs, consistent with a mixture of collisional and background radiation excitation of the observed H 2 rotational levels. Using Voigt profile fits to absorption lines from a range of singly ionized heavy elements we find eight components covering a Velocity range of ∼110 km s ―1 , with a further outlier over 120 km s ―1 away from the nearest in the main group. The H I structure is expected to follow some combination of the singly ionized and neutral gas, but the 21-cm absorption profile is considerably different. We suggest, as have others, that this may be because the different extent and brightness distributions of the radio and optical background sources mean that the sightlines are not the same, and so the spin temperature derived by comparing the Lyα and 21-cm line strengths has little physical meaning. The neutral and singly ionized heavy element line profiles also show significant differences, and so the dominant components in each appear to be physically distinct. Attempts to use the range of atomic masses to separate thermal and turbulent components of their Doppler widths were not generally successful, since there are several blended components and the useful mass range (about a factor of 2) is not very large. The Velocity structure in all ionization stages up to +3, apart from the neutral heavy elements, is sufficiently Complex that it is difficult to separate out the corresponding Velocity components for different ionization levels and determine their column densities.
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A cold component and the Complex Velocity structure of DLA1331 + 170
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Robert F. Carswell, Regina A. Jorgenson, Arthur M. Wolfe, Michael T. MurphyAbstract:We examine the Velocity structure in the gas associated with H I in the damped Lyα absorption system at redshift z = 1.7764 towards the QSO 1331 + 170 using Arecibo H i 21-cm data, optical spectra from the Keck High Resolution Echelle Spectrograph (HIRES) and European Southern Observatory (ESO) Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES), and a previously published Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) ultraviolet spectrum. From the optical data we find at least two, and possibly three, components showing C I lines. One of these has very narrow lines with Doppler parameter b = 0.55 km s ―1 , corresponding to a kinetic temperature of 220 K if the broadening is thermal and with a 2σ upper limit of 480 K. We re-examine the H 2 analysis undertaken by Cui et al. using the neutral carbon Velocity structure, and find a model which is, unlike theirs, consistent with a mixture of collisional and background radiation excitation of the observed H 2 rotational levels. Using Voigt profile fits to absorption lines from a range of singly ionized heavy elements we find eight components covering a Velocity range of ∼110 km s ―1 , with a further outlier over 120 km s ―1 away from the nearest in the main group. The H I structure is expected to follow some combination of the singly ionized and neutral gas, but the 21-cm absorption profile is considerably different. We suggest, as have others, that this may be because the different extent and brightness distributions of the radio and optical background sources mean that the sightlines are not the same, and so the spin temperature derived by comparing the Lyα and 21-cm line strengths has little physical meaning. The neutral and singly ionized heavy element line profiles also show significant differences, and so the dominant components in each appear to be physically distinct. Attempts to use the range of atomic masses to separate thermal and turbulent components of their Doppler widths were not generally successful, since there are several blended components and the useful mass range (about a factor of 2) is not very large. The Velocity structure in all ionization stages up to +3, apart from the neutral heavy elements, is sufficiently Complex that it is difficult to separate out the corresponding Velocity components for different ionization levels and determine their column densities.
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a cold component and the Complex Velocity structure of dla1331 170
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Robert F. Carswell, Regina A. Jorgenson, Arthur M. Wolfe, Michael T. MurphyAbstract:[ABRIDGED] We examine the Velocity structure in the gas associated with \ion{H}{1} in the damped Ly$\alpha$ absorption system at redshift $z=1.7764$ towards the QSO $1331+170$ using 21cm data, optical and STIS spectra. We find at least two, and possibly three, components showing \ion{C}{1} lines. One of these has Doppler parameter $b=0.55${\kms}, corresponding to a kinetic temperature of 220K if the broadening is thermal. We re-examine the H$_2$ analysis undertaken by \citet{Cui05} using the neutral carbon Velocity structure, and find a model which is, consistent with a mixture of collisional and background radiation excitation of the observed H$_2$ rotational levels. For singly ionized heavy elements we find eight components covering a Velocity range of $\sim 110$ {\kms}. The \ion{H}{1} structure is expected to follow some combination of the singly ionized and neutral gas, but the 21cm absorption profile is considerably different. This may be because of the different extent and brightness distributions of the radio and optical background sources, and so the spin temperature derived by comparing the Ly$\alpha$ and 21cm line strengths has little physical meaning. The neutral and singly ionized heavy element line profiles also show significant differences, and so the dominant components in each appear to be physically distinct. Attempts to use the range of atomic masses to separate thermal and turbulent components of their Doppler widths were not generally successful. The Velocity structure in all ionization stages up to $+3$, apart from the neutral heavy elements, is sufficiently Complex that it is difficult to separate out the corresponding Velocity components for different ionization levels and determine their column densities.
Robert F. Carswell - One of the best experts on this subject based on the ideXlab platform.
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a cold component and the Complex Velocity structure of dla1331 170
Monthly Notices of the Royal Astronomical Society, 2011Co-Authors: Robert F. Carswell, Regina A. Jorgenson, Arthur M. Wolfe, Michael T. MurphyAbstract:We examine the Velocity structure in the gas associated with H I in the damped Lyα absorption system at redshift z = 1.7764 towards the QSO 1331 + 170 using Arecibo H i 21-cm data, optical spectra from the Keck High Resolution Echelle Spectrograph (HIRES) and European Southern Observatory (ESO) Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES), and a previously published Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) ultraviolet spectrum. From the optical data we find at least two, and possibly three, components showing C I lines. One of these has very narrow lines with Doppler parameter b = 0.55 km s ―1 , corresponding to a kinetic temperature of 220 K if the broadening is thermal and with a 2σ upper limit of 480 K. We re-examine the H 2 analysis undertaken by Cui et al. using the neutral carbon Velocity structure, and find a model which is, unlike theirs, consistent with a mixture of collisional and background radiation excitation of the observed H 2 rotational levels. Using Voigt profile fits to absorption lines from a range of singly ionized heavy elements we find eight components covering a Velocity range of ∼110 km s ―1 , with a further outlier over 120 km s ―1 away from the nearest in the main group. The H I structure is expected to follow some combination of the singly ionized and neutral gas, but the 21-cm absorption profile is considerably different. We suggest, as have others, that this may be because the different extent and brightness distributions of the radio and optical background sources mean that the sightlines are not the same, and so the spin temperature derived by comparing the Lyα and 21-cm line strengths has little physical meaning. The neutral and singly ionized heavy element line profiles also show significant differences, and so the dominant components in each appear to be physically distinct. Attempts to use the range of atomic masses to separate thermal and turbulent components of their Doppler widths were not generally successful, since there are several blended components and the useful mass range (about a factor of 2) is not very large. The Velocity structure in all ionization stages up to +3, apart from the neutral heavy elements, is sufficiently Complex that it is difficult to separate out the corresponding Velocity components for different ionization levels and determine their column densities.
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A cold component and the Complex Velocity structure of DLA1331 + 170
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Robert F. Carswell, Regina A. Jorgenson, Arthur M. Wolfe, Michael T. MurphyAbstract:We examine the Velocity structure in the gas associated with H I in the damped Lyα absorption system at redshift z = 1.7764 towards the QSO 1331 + 170 using Arecibo H i 21-cm data, optical spectra from the Keck High Resolution Echelle Spectrograph (HIRES) and European Southern Observatory (ESO) Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES), and a previously published Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) ultraviolet spectrum. From the optical data we find at least two, and possibly three, components showing C I lines. One of these has very narrow lines with Doppler parameter b = 0.55 km s ―1 , corresponding to a kinetic temperature of 220 K if the broadening is thermal and with a 2σ upper limit of 480 K. We re-examine the H 2 analysis undertaken by Cui et al. using the neutral carbon Velocity structure, and find a model which is, unlike theirs, consistent with a mixture of collisional and background radiation excitation of the observed H 2 rotational levels. Using Voigt profile fits to absorption lines from a range of singly ionized heavy elements we find eight components covering a Velocity range of ∼110 km s ―1 , with a further outlier over 120 km s ―1 away from the nearest in the main group. The H I structure is expected to follow some combination of the singly ionized and neutral gas, but the 21-cm absorption profile is considerably different. We suggest, as have others, that this may be because the different extent and brightness distributions of the radio and optical background sources mean that the sightlines are not the same, and so the spin temperature derived by comparing the Lyα and 21-cm line strengths has little physical meaning. The neutral and singly ionized heavy element line profiles also show significant differences, and so the dominant components in each appear to be physically distinct. Attempts to use the range of atomic masses to separate thermal and turbulent components of their Doppler widths were not generally successful, since there are several blended components and the useful mass range (about a factor of 2) is not very large. The Velocity structure in all ionization stages up to +3, apart from the neutral heavy elements, is sufficiently Complex that it is difficult to separate out the corresponding Velocity components for different ionization levels and determine their column densities.
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a cold component and the Complex Velocity structure of dla1331 170
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Robert F. Carswell, Regina A. Jorgenson, Arthur M. Wolfe, Michael T. MurphyAbstract:[ABRIDGED] We examine the Velocity structure in the gas associated with \ion{H}{1} in the damped Ly$\alpha$ absorption system at redshift $z=1.7764$ towards the QSO $1331+170$ using 21cm data, optical and STIS spectra. We find at least two, and possibly three, components showing \ion{C}{1} lines. One of these has Doppler parameter $b=0.55${\kms}, corresponding to a kinetic temperature of 220K if the broadening is thermal. We re-examine the H$_2$ analysis undertaken by \citet{Cui05} using the neutral carbon Velocity structure, and find a model which is, consistent with a mixture of collisional and background radiation excitation of the observed H$_2$ rotational levels. For singly ionized heavy elements we find eight components covering a Velocity range of $\sim 110$ {\kms}. The \ion{H}{1} structure is expected to follow some combination of the singly ionized and neutral gas, but the 21cm absorption profile is considerably different. This may be because of the different extent and brightness distributions of the radio and optical background sources, and so the spin temperature derived by comparing the Ly$\alpha$ and 21cm line strengths has little physical meaning. The neutral and singly ionized heavy element line profiles also show significant differences, and so the dominant components in each appear to be physically distinct. Attempts to use the range of atomic masses to separate thermal and turbulent components of their Doppler widths were not generally successful. The Velocity structure in all ionization stages up to $+3$, apart from the neutral heavy elements, is sufficiently Complex that it is difficult to separate out the corresponding Velocity components for different ionization levels and determine their column densities.
Yang Liu - One of the best experts on this subject based on the ideXlab platform.
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Viscoelastic Wave Simulation with High Temporal Accuracy Using Frequency-Dependent Complex Velocity
Surveys in Geophysics, 2020Co-Authors: Yabing Zhang, Yang LiuAbstract:In recent decades, the study of seismic attenuation has received more and more concerns because it can stimulate the development of wave propagation simulation and improve the accuracy of structure imaging and reservoir prediction. In this paper, we review the attenuation theory and the development of high temporal accuracy wave simulation. The conventional mathematical models to describe the characteristics of viscoelastic are based on constant-Q model or standard linear solids theory. However, these approaches possess some noticeable shortcomings. Therefore, we introduce a frequency-dependent Complex Velocity to derive the novel viscoelastic wave equations with decoupled amplitude dissipation and phase dispersion. To obtain high temporal accuracy viscoelastic wave simulation, we adopt the normalized pseudo-Laplacian to compensate for the temporal dispersion errors caused by the second-order finite-difference discretization in the time domain. During the implementation, we incorporate the normalized pseudo-Laplacian into the optimized staggered-grid finite-difference coefficients. Therefore, it can greatly reduce the times of low-rank decomposition and Fourier transform and largely improve the computational efficiency. Based on this strategy, we can implement the high temporal accuracy viscoelastic wavefield extrapolation by comprehensively exploiting the staggered-grid finite-difference scheme, pseudo-spectral method and low-rank decomposition algorithm. Meanwhile, a linear Velocity model is employed to evaluate the accuracy of low-rank approximation. Furthermore, we use several numerical examples to carry out the comparison between our scheme and other conventional methods. The numerical results reveal that our proposed scheme can effectively compensate for temporal dispersion errors and help generate high temporal accuracy viscoelastic wave solutions.
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Anisotropic viscoacoustic wave modelling in VTI media using frequency-dependent Complex Velocity
Journal of Geophysics and Engineering, 2020Co-Authors: Yabing Zhang, Yang LiuAbstract:Abstract Under the conditions of acoustic approximation and isotropic attenuation, we derive the pseudo- and pure-viscoacoustic wave equations from the Complex constitutive equation and the decoupled P-wave dispersion relation, respectively. Based on the equations, we investigate the viscoacoustic wave propagation in vertical transversely isotropic media. The favourable advantage of these formulas is that the phase dispersion and the amplitude dissipation terms are inherently separated. As a result, we can conveniently perform the decoupled viscoacoustic wavefield simulations by choosing different coefficients. In the computational process, a generalised pseudo-spectral method and a low-rank decomposition scheme are adopted to calculate the wavenumber-domain and mixed-domain propagators, respectively. Because low-rank decomposition plays an important role in the simulated procedure, we evaluate the approximation accuracy for different operators using a linear Velocity model. To demonstrate the effectiveness and the accuracy of our method, several numerical examples are carried out based on the new pseudo- and pure-viscoacoustic wave equations. Both equations can effectively describe the viscoacoustic wave propagation characteristics in vertical transversely isotropic media. Unlike the pseudo-viscoacoustic wave equation, the pure-viscoacoustic wave equation can produce stable viscoacoustic wavefields without any SV-wave artefacts.
Regina A. Jorgenson - One of the best experts on this subject based on the ideXlab platform.
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a cold component and the Complex Velocity structure of dla1331 170
Monthly Notices of the Royal Astronomical Society, 2011Co-Authors: Robert F. Carswell, Regina A. Jorgenson, Arthur M. Wolfe, Michael T. MurphyAbstract:We examine the Velocity structure in the gas associated with H I in the damped Lyα absorption system at redshift z = 1.7764 towards the QSO 1331 + 170 using Arecibo H i 21-cm data, optical spectra from the Keck High Resolution Echelle Spectrograph (HIRES) and European Southern Observatory (ESO) Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES), and a previously published Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) ultraviolet spectrum. From the optical data we find at least two, and possibly three, components showing C I lines. One of these has very narrow lines with Doppler parameter b = 0.55 km s ―1 , corresponding to a kinetic temperature of 220 K if the broadening is thermal and with a 2σ upper limit of 480 K. We re-examine the H 2 analysis undertaken by Cui et al. using the neutral carbon Velocity structure, and find a model which is, unlike theirs, consistent with a mixture of collisional and background radiation excitation of the observed H 2 rotational levels. Using Voigt profile fits to absorption lines from a range of singly ionized heavy elements we find eight components covering a Velocity range of ∼110 km s ―1 , with a further outlier over 120 km s ―1 away from the nearest in the main group. The H I structure is expected to follow some combination of the singly ionized and neutral gas, but the 21-cm absorption profile is considerably different. We suggest, as have others, that this may be because the different extent and brightness distributions of the radio and optical background sources mean that the sightlines are not the same, and so the spin temperature derived by comparing the Lyα and 21-cm line strengths has little physical meaning. The neutral and singly ionized heavy element line profiles also show significant differences, and so the dominant components in each appear to be physically distinct. Attempts to use the range of atomic masses to separate thermal and turbulent components of their Doppler widths were not generally successful, since there are several blended components and the useful mass range (about a factor of 2) is not very large. The Velocity structure in all ionization stages up to +3, apart from the neutral heavy elements, is sufficiently Complex that it is difficult to separate out the corresponding Velocity components for different ionization levels and determine their column densities.
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A cold component and the Complex Velocity structure of DLA1331 + 170
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Robert F. Carswell, Regina A. Jorgenson, Arthur M. Wolfe, Michael T. MurphyAbstract:We examine the Velocity structure in the gas associated with H I in the damped Lyα absorption system at redshift z = 1.7764 towards the QSO 1331 + 170 using Arecibo H i 21-cm data, optical spectra from the Keck High Resolution Echelle Spectrograph (HIRES) and European Southern Observatory (ESO) Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES), and a previously published Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) ultraviolet spectrum. From the optical data we find at least two, and possibly three, components showing C I lines. One of these has very narrow lines with Doppler parameter b = 0.55 km s ―1 , corresponding to a kinetic temperature of 220 K if the broadening is thermal and with a 2σ upper limit of 480 K. We re-examine the H 2 analysis undertaken by Cui et al. using the neutral carbon Velocity structure, and find a model which is, unlike theirs, consistent with a mixture of collisional and background radiation excitation of the observed H 2 rotational levels. Using Voigt profile fits to absorption lines from a range of singly ionized heavy elements we find eight components covering a Velocity range of ∼110 km s ―1 , with a further outlier over 120 km s ―1 away from the nearest in the main group. The H I structure is expected to follow some combination of the singly ionized and neutral gas, but the 21-cm absorption profile is considerably different. We suggest, as have others, that this may be because the different extent and brightness distributions of the radio and optical background sources mean that the sightlines are not the same, and so the spin temperature derived by comparing the Lyα and 21-cm line strengths has little physical meaning. The neutral and singly ionized heavy element line profiles also show significant differences, and so the dominant components in each appear to be physically distinct. Attempts to use the range of atomic masses to separate thermal and turbulent components of their Doppler widths were not generally successful, since there are several blended components and the useful mass range (about a factor of 2) is not very large. The Velocity structure in all ionization stages up to +3, apart from the neutral heavy elements, is sufficiently Complex that it is difficult to separate out the corresponding Velocity components for different ionization levels and determine their column densities.
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a cold component and the Complex Velocity structure of dla1331 170
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Robert F. Carswell, Regina A. Jorgenson, Arthur M. Wolfe, Michael T. MurphyAbstract:[ABRIDGED] We examine the Velocity structure in the gas associated with \ion{H}{1} in the damped Ly$\alpha$ absorption system at redshift $z=1.7764$ towards the QSO $1331+170$ using 21cm data, optical and STIS spectra. We find at least two, and possibly three, components showing \ion{C}{1} lines. One of these has Doppler parameter $b=0.55${\kms}, corresponding to a kinetic temperature of 220K if the broadening is thermal. We re-examine the H$_2$ analysis undertaken by \citet{Cui05} using the neutral carbon Velocity structure, and find a model which is, consistent with a mixture of collisional and background radiation excitation of the observed H$_2$ rotational levels. For singly ionized heavy elements we find eight components covering a Velocity range of $\sim 110$ {\kms}. The \ion{H}{1} structure is expected to follow some combination of the singly ionized and neutral gas, but the 21cm absorption profile is considerably different. This may be because of the different extent and brightness distributions of the radio and optical background sources, and so the spin temperature derived by comparing the Ly$\alpha$ and 21cm line strengths has little physical meaning. The neutral and singly ionized heavy element line profiles also show significant differences, and so the dominant components in each appear to be physically distinct. Attempts to use the range of atomic masses to separate thermal and turbulent components of their Doppler widths were not generally successful. The Velocity structure in all ionization stages up to $+3$, apart from the neutral heavy elements, is sufficiently Complex that it is difficult to separate out the corresponding Velocity components for different ionization levels and determine their column densities.
Arthur M. Wolfe - One of the best experts on this subject based on the ideXlab platform.
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a cold component and the Complex Velocity structure of dla1331 170
Monthly Notices of the Royal Astronomical Society, 2011Co-Authors: Robert F. Carswell, Regina A. Jorgenson, Arthur M. Wolfe, Michael T. MurphyAbstract:We examine the Velocity structure in the gas associated with H I in the damped Lyα absorption system at redshift z = 1.7764 towards the QSO 1331 + 170 using Arecibo H i 21-cm data, optical spectra from the Keck High Resolution Echelle Spectrograph (HIRES) and European Southern Observatory (ESO) Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES), and a previously published Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) ultraviolet spectrum. From the optical data we find at least two, and possibly three, components showing C I lines. One of these has very narrow lines with Doppler parameter b = 0.55 km s ―1 , corresponding to a kinetic temperature of 220 K if the broadening is thermal and with a 2σ upper limit of 480 K. We re-examine the H 2 analysis undertaken by Cui et al. using the neutral carbon Velocity structure, and find a model which is, unlike theirs, consistent with a mixture of collisional and background radiation excitation of the observed H 2 rotational levels. Using Voigt profile fits to absorption lines from a range of singly ionized heavy elements we find eight components covering a Velocity range of ∼110 km s ―1 , with a further outlier over 120 km s ―1 away from the nearest in the main group. The H I structure is expected to follow some combination of the singly ionized and neutral gas, but the 21-cm absorption profile is considerably different. We suggest, as have others, that this may be because the different extent and brightness distributions of the radio and optical background sources mean that the sightlines are not the same, and so the spin temperature derived by comparing the Lyα and 21-cm line strengths has little physical meaning. The neutral and singly ionized heavy element line profiles also show significant differences, and so the dominant components in each appear to be physically distinct. Attempts to use the range of atomic masses to separate thermal and turbulent components of their Doppler widths were not generally successful, since there are several blended components and the useful mass range (about a factor of 2) is not very large. The Velocity structure in all ionization stages up to +3, apart from the neutral heavy elements, is sufficiently Complex that it is difficult to separate out the corresponding Velocity components for different ionization levels and determine their column densities.
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A cold component and the Complex Velocity structure of DLA1331 + 170
Monthly Notices of the Royal Astronomical Society, 2010Co-Authors: Robert F. Carswell, Regina A. Jorgenson, Arthur M. Wolfe, Michael T. MurphyAbstract:We examine the Velocity structure in the gas associated with H I in the damped Lyα absorption system at redshift z = 1.7764 towards the QSO 1331 + 170 using Arecibo H i 21-cm data, optical spectra from the Keck High Resolution Echelle Spectrograph (HIRES) and European Southern Observatory (ESO) Very Large Telescope (VLT) Ultraviolet and Visual Echelle Spectrograph (UVES), and a previously published Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) ultraviolet spectrum. From the optical data we find at least two, and possibly three, components showing C I lines. One of these has very narrow lines with Doppler parameter b = 0.55 km s ―1 , corresponding to a kinetic temperature of 220 K if the broadening is thermal and with a 2σ upper limit of 480 K. We re-examine the H 2 analysis undertaken by Cui et al. using the neutral carbon Velocity structure, and find a model which is, unlike theirs, consistent with a mixture of collisional and background radiation excitation of the observed H 2 rotational levels. Using Voigt profile fits to absorption lines from a range of singly ionized heavy elements we find eight components covering a Velocity range of ∼110 km s ―1 , with a further outlier over 120 km s ―1 away from the nearest in the main group. The H I structure is expected to follow some combination of the singly ionized and neutral gas, but the 21-cm absorption profile is considerably different. We suggest, as have others, that this may be because the different extent and brightness distributions of the radio and optical background sources mean that the sightlines are not the same, and so the spin temperature derived by comparing the Lyα and 21-cm line strengths has little physical meaning. The neutral and singly ionized heavy element line profiles also show significant differences, and so the dominant components in each appear to be physically distinct. Attempts to use the range of atomic masses to separate thermal and turbulent components of their Doppler widths were not generally successful, since there are several blended components and the useful mass range (about a factor of 2) is not very large. The Velocity structure in all ionization stages up to +3, apart from the neutral heavy elements, is sufficiently Complex that it is difficult to separate out the corresponding Velocity components for different ionization levels and determine their column densities.
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a cold component and the Complex Velocity structure of dla1331 170
arXiv: Cosmology and Nongalactic Astrophysics, 2010Co-Authors: Robert F. Carswell, Regina A. Jorgenson, Arthur M. Wolfe, Michael T. MurphyAbstract:[ABRIDGED] We examine the Velocity structure in the gas associated with \ion{H}{1} in the damped Ly$\alpha$ absorption system at redshift $z=1.7764$ towards the QSO $1331+170$ using 21cm data, optical and STIS spectra. We find at least two, and possibly three, components showing \ion{C}{1} lines. One of these has Doppler parameter $b=0.55${\kms}, corresponding to a kinetic temperature of 220K if the broadening is thermal. We re-examine the H$_2$ analysis undertaken by \citet{Cui05} using the neutral carbon Velocity structure, and find a model which is, consistent with a mixture of collisional and background radiation excitation of the observed H$_2$ rotational levels. For singly ionized heavy elements we find eight components covering a Velocity range of $\sim 110$ {\kms}. The \ion{H}{1} structure is expected to follow some combination of the singly ionized and neutral gas, but the 21cm absorption profile is considerably different. This may be because of the different extent and brightness distributions of the radio and optical background sources, and so the spin temperature derived by comparing the Ly$\alpha$ and 21cm line strengths has little physical meaning. The neutral and singly ionized heavy element line profiles also show significant differences, and so the dominant components in each appear to be physically distinct. Attempts to use the range of atomic masses to separate thermal and turbulent components of their Doppler widths were not generally successful. The Velocity structure in all ionization stages up to $+3$, apart from the neutral heavy elements, is sufficiently Complex that it is difficult to separate out the corresponding Velocity components for different ionization levels and determine their column densities.