New Temperatures of Diffuse Interstellar Gas: Thermally Unstable Gas

Heiles, Carl

doi:10.1086/319844

Cited by 82 publications

(77 citation statements)

References 19 publications

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“…Accurate Arecibo 21 cm measurements of H i spin temperatures in the ISM reveal strong evidence for CNM gas with T ¼ 25 50 K but no evidence for WNM gas with T > 7000 K. Rather, a significant fraction of the warm gas lies in the thermally unstable regime with T ¼ 500 5000 K (Heiles 2001). While these measurements do not rule out multiphase models for the ISM, they bring to mind alternative scenarios.…”

Section: No 1 2003mentioning

confidence: 81%

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Cii* Absorption in Damped Lyα Systems. I. Star Formation Rates in a Two‐Phase Medium

Wolfe

Prochaska

Gawiser

2003

ApJ

160

261

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We describe a technique that for the first time measures star formation rates (SFRs) in damped Ly systems (DLAs) directly. We assume that massive stars form in DLAs and that the far-ultraviolet (FUV) radiation they emit heats the gas by the grain photoelectric mechanism. We infer the heating rate by equating it to the cooling rate measured by the strength of C ii* 1335.7 absorption. Since the heating rate is proportional to the product of the dust-to-gas ratio, the grain photoelectric heating efficiency, and the SFR per unit area, _ Ã Ã , we can deduce _ Ã Ã for DLAs in which the cooling rate and dust-to-gas ratio have been measured. We consider models in which the dust consists of carbonaceous grains and silicate grains. We present twophase models in which the cold neutral medium (CNM) and warm neutral medium (WNM) are in pressure equilibrium. In the CNM model the line of sight passes through CNM and WNM gas, while in the WNM model the line of sight passes only through WNM gas. Since the grain photoelectric heating efficiency is at least an order of magnitude higher in the CNM than in the WNM, most of the C ii* absorption arises in the CNM in the CNM model. We use the measured C ii* absorption lines to derive _ Ã Ã for a sample of %30 DLAs in which has been inferred from element depletion patterns. We show that the inferred _ Ã Ã corresponds to an average over the star-forming volume of the DLA rather than to local star formation along the line of sight. We obtain the average _ Ã Ã and show that _ Ã Ã ¼ 10 À2:2 M yr À1 kpc À2 for the CNM solution and _ Ã Ã ¼ 10 À1:3 M yr À1 kpc À2 for the WNM solution. Interestingly, the SFR per unit area in the CNM solution is similar to that measured in the Milky Way interstellar medium.

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Section: No 1 2003mentioning

confidence: 81%

“…The nonthermal component consists of extragalactic power-law radiation. These X-rays penetrate the outsides of CNM clouds, heating the gas to form the WNM (e.g., Heiles 2001). W95 assume that the incident X-rays are attenuated by a WNM layer of gas with H i column density log 10 N w ¼ 19 cm À2 .…”

Section: Heatingmentioning

confidence: 99%

Cii* Absorption in Damped Lyα Systems. I. Star Formation Rates in a Two‐Phase Medium

Wolfe

Prochaska

Gawiser

2003

ApJ

160

261

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“…The figure is centered on the galactic center, with longitude increasing toward the left. The polarization data are from the sources listed in Section 3 and Heiles (2001). (A color version of this figure is available in the online journal.)…”

Section: Polarization Data Used In the Studymentioning

confidence: 99%

The Interstellar Magnetic Field Close to the Sun. Ii.

Frisch

Andersson

Berdyugin

et al. 2012

ApJ

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The magnetic field in the local interstellar medium (ISM) provides a key indicator of the galactic environment of the Sun and influences the shape of the heliosphere. We have studied the interstellar magnetic field (ISMF) in the solar vicinity using polarized starlight for stars within 40 pc of the Sun and 90 • of the heliosphere nose. In Frisch et al. (Paper I), we developed a method for determining the local ISMF direction by finding the best match to a group of interstellar polarization position angles obtained toward nearby stars, based on the assumption that the polarization is parallel to the ISMF. In this paper, we extend the analysis by utilizing weighted fits to the position angles and by including new observations acquired for this study. We find that the local ISMF is pointed toward the • 25 pc −1 . This conclusion is conditioned on the small sample of stars available for defining this rotation. Variations from the ordered component suggest a turbulent component of ∼23 • . The ordered component and standard relations between polarization, color excess, and H o column density predict a reasonable increase of N(H) with distance in the local ISM. The similarity of the ISMF directions traced by the polarizations, the IBEX Ribbon, and pulsars inside the Local Bubble in the third galactic quadrant suggest that the ISMF is relatively uniform over spatial scales of 8-200 pc and is more similar to interarm than spiral-arm magnetic fields. The ISMF direction from the polarization data is also consistent with small-scale spatial asymmetries detected in GeV-TeV cosmic rays with a galactic origin. The peculiar geometrical relation found earlier between the cosmic microwave background dipole moment, the heliosphere nose, and the ISMF direction is supported by this study. The interstellar radiation field at ∼975 Å does not appear to play a role in grain alignment for the low-density ISM studied here.

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“…One technique for measuring the spin temperature of H I is to fit 21 cm emission and absorption data with a collection of independent isothermal Gaussian components. With this technique, H I spin temperatures have been measured in the range of ∼10-3000 K (e.g., Dickey et al 1978Dickey et al , 2003Crovisier et al 1980;Mebold et al 1982;Kalberla et al 1985;Heiles 2001;Heiles & Troland 2003;Begum et al 2010;Roy et al 2013). Although Galactic H I surveys have constrained the cold end of the ISM spin temperature distribution with hundreds of detected CNMtemperature components, few components have been detected with temperatures consistent with the WNM.…”

Section: Introduction: 21 CM Gaussian Fitsmentioning

confidence: 99%

Autonomous Gaussian Decomposition

Lindner¹,

Vera-Ciro²,

Murray³

et al. 2015

Self Cite

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We present a new algorithm, named Autonomous Gaussian Decomposition (AGD), for automatically decomposing spectra into Gaussian components. AGD uses derivative spectroscopy and machine learning to provide optimized guesses for the number of Gaussian components in the data, and also their locations, widths, and amplitudes. We test AGD and find that it produces results comparable to human-derived solutions on 21 cm absorption spectra from the 21 cm SPectral line Observations of Neutral Gas with the EVLA (21-SPONGE) survey. We use AGD with Monte Carlo methods to derive the H I line completeness as a function of peak optical depth and velocity width for the 21-SPONGE data, and also show that the results of AGD are stable against varying observational noise intensity. The autonomy and computational efficiency of the method over traditional manual Gaussian fits allow for truly unbiased comparisons between observations and simulations, and for the ability to scale up and interpret the very large data volumes from the upcoming Square Kilometer Array and pathfinder telescopes.

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New Temperatures of Diffuse Interstellar Gas: Thermally Unstable Gas

Cited by 82 publications

References 19 publications

Cii* Absorption in Damped Lyα Systems. I. Star Formation Rates in a Two‐Phase Medium

Cii* Absorption in Damped Lyα Systems. I. Star Formation Rates in a Two‐Phase Medium

The Interstellar Magnetic Field Close to the Sun. Ii.

Autonomous Gaussian Decomposition

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