Pressure and Ionization Balances in the Circum-Heliospheric Interstellar Medium and the Local Bubble

Jenkins, Edward B.

doi:10.1007/s11214-008-9352-1

Cited by 22 publications

(15 citation statements)

References 77 publications

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“…Such conditions are very rare among the 2416 C i parcels sampled by Jenkins & Tripp (2011)-less than 1% of these clouds have (f 1, f 2) excitation values corresponding to temperatures less than 30 K and pressures greater than 10,000 cm −3 K. The highly pressurized nature of the LLCC is particularly intriguing given its location deep inside the Local Bubble. As reviewed by Jenkins (2009b) and Welsh & Shelton (2009), the pressure balance of interstellar gas in this environment has long been a contentious issue. Since the discovery of the diffuse soft X-ray background in the 1970s, numerous studies through the 1990s interpreted it in terms of hot gas filling the Local Bubble with a pressure somewhere between 10,000 and 20,000 cm Unlike the Cl i profile where the LLCC absorption stands alone, the Cr ii, Ni ii, Zn ii, S ii, and C ii * profiles all show significant blueward absorption arising from gas beyond the LLCC.…”

Section: The Llcc C I Fine-structure Excitationmentioning

confidence: 99%

The Remarkable High Pressure of the Local Leo Cold Cloud

Meyer

Lauroesch

Peek

et al. 2012

ApJ

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Using the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope, we have obtained high-resolution ultraviolet spectra of the C i absorption toward two stars behind the Local Leo Cold Cloud (LLCC). At a distance (≈20 pc) that places it well inside the Local Bubble, the LLCC is the nearest example of the coldest known (T ≈ 20 K) diffuse interstellar clouds. The STIS measurements of the C i fine-structure excitation toward HD 85259 and HD 83023 indicate that the thermal gas pressure of the LLCC is much greater than that of the warm clouds in the Local Bubble. The mean LLCC pressure measured toward these two stars (60,000 cm −3 K) implies an H i density of ≈3000 cm −3 and a cloud thickness of ≈200 AU at the 20 K cloud temperature. Such a thin, cold, dense structure could arise at the collision interface between converging flows of warm gas. However, the measured LLCC pressure is appreciably higher than that expected in the colliding-cloud interpretation given the velocity and column density constraints on warm clouds in the HD 85259 and HD 83023 sightlines. Additional STIS measurements of the Zn ii, Ni ii, and Cr ii column densities toward HD 85259 indicate that the LLCC has a modest "warm cloud" dust depletion pattern consistent with its low dust-to-gas ratio determined from H i 21 cm and 100 μm observations. In support of the inferred sheet-like geometry for the LLCC, a multi-epoch comparison of the Na i absorption toward a high-proper-motion background star reveals a 40% column density variation indicative of LLCC Na i structure on a scale of ≈50 AU.

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Section: The Llcc C I Fine-structure Excitationmentioning

confidence: 99%

The Remarkable High Pressure of the Local Leo Cold Cloud

Meyer

Lauroesch

Peek

et al. 2012

ApJ

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“…Since one might expect to encounter more than one conductive cloud interface over the > 40 pc sight-lines in which FUSE has detected O VI, then the observations suggest that something may be reducing the effectiveness of thermal conduction in these O VI-producing interfaces. Jenkins (2008) has proposed that local clouds could mutually shield each other from the effects of a hot Local Bubble plasma, such that a conduction front suitable for the formation of O VI only occurs at the very periphery of the cloud grouping. Alternately, others have shown the importance of magnetic fields in their ability to inhibit conduction (Slavin 1989;Cox and Helenius 2003).…”

Section: Transition Temperature Gas: O VImentioning

confidence: 99%

“…However, even with conservative revisions to these data, the spectre of a pressure imbalance still remains. A more thorough discussion of the issues that arise from this apparent pressure imbalance can be found in Jenkins (2008).…”

Section: Thermal Pressure Of the Hot Gasmentioning

confidence: 99%

The trouble with the Local Bubble

Welsh

Shelton

2009

Astrophys Space Sci

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The model of a Local Hot Bubble has been widely accepted as providing a framework that can explain the ubiquitous presence of the soft X-ray background diffuse emission. We summarize the current knowledge on this local interstellar region, paying particular reference to observations that sample emission from the presumed local million degree K hot plasma. However, we have listed numerous observations that are seemingly in conflict with the concept of a hot Local Bubble. In particular, the discovery of solar wind charge exchange that can generate an appreciable soft X-ray background signal within the heliosphere, has led to a reassessment of the generally accepted model that requires a hot local plasma.In order to explain the majority of observations of the local plasma, we forward two new speculative models that describe the physical state of the local interstellar gas. One possible scenario is similar to the present widely accepted model of the Local Hot Bubble, except that it accounts for only 50% of the soft X-ray emission currently detected in the galactic plane, has a lower thermal pressure than previously thought, and its hot plasma is not as hot as previously believed. Although such a model can solve several difficulties with the traditional hot Local Bubble model, a heating mechanism for the dimmer and cooler gas remains to be found. The second possible explanation is that of the 'Hot Top' model, in which the Local Cavity is an old su-B.Y. Welsh ( ) Space Sciences Laboratory, University of California, 7 Gauss Way, Berkeley, CA 94720, USA e-mail: bwelsh@ssl.berkeley.edu R.L. Shelton Department of Physics and Astronomy, University of Georgia, Athens, GA 30602, USA pernova remnant in which no (or very little) million degree local plasma is presently required. Instead, the cavity is now thought to be filled with partially ionized cloudlets of temperature ∼ 7000 K that are surrounded by lower density envelopes of photo-ionized gas of temperature ∼ 20,000 K. Although this new scenario provides a natural explanation for many of the observations that were in conflict with the Local Hot Bubble model, we cannot (as yet) provide a satisfactory explanation or the emission levels observed in the B and Be ultra-soft X-ray bands.

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“…Koutroumpa et al 2009). Decreasing the hot gas pressure significantly would have the positive effect of suppressing the strong difference from the pressure measured within the diffuse clouds and the local cloud (Jenkins 2009). From 3D gas and dust mapping one can expect significant progresses on these topics, the "Local Bubble" wall location and the X-ray emission source regions, some hints about the local bubble formation and the link between the local bubble and surrounding bubbles and more generally a better understanding of the multi-phase structure and the interaction between the different phases of the ISM.…”

Section: Introductionmentioning

confidence: 99%

Spatial distribution of interstellar dust in the Sun's vicinity

Vergely¹,

Valette

Lallement

et al. 2010

A&A

107

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Aims. 3D tomography of the interstellar dust and gas may be useful in many respects, from the physical and chemical evolution of the interstellar medium itself to foreground decontamination of the cosmic microwave background, or various studies of the environments of specific objects. However, while spectral data cubes of the galactic emission become increasingly precise, the information on the distance to the emitting regions has not progressed as well and relies essentially on the galactic rotation curve. Our goal here is to bring more precise information on the distance to nearby interstellar dust and gas clouds within 250 pc. Methods. We apply the best available calibration methods to a carefully screened set of stellar Strömgren photometry data for targets possessing a Hipparcos parallax and spectral type classification. We combine the derived interstellar extinctions and the parallax distances for about 6000 stars to build a 3D tomography of the local dust. We use an inversion method based on a regularized Bayesian approach and a least squares criterion, optimized for this specific data set. We apply the same inversion technique to a totally independent set of neutral sodium absorption data available for about 1700 target stars. Results. We obtain 3D maps of the opacity and the distance to the main dust-bearing clouds within 250 pc and identify in those maps well-known dark clouds and high galactic more diffuse entities. We calculate the integrated extinction between the Sun and the cube boundary and compare this with the total galactic extinction derived from infrared 2D maps. The two quantities reach similar values at high latitudes, as expected if the local dust content is satisfyingly reproduced and the dust is closer than 250 pc. Those maps show a larger high latitude dust opacity in the North compared to the South, reinforcing earlier evidences. Interestingly the gas maps do not show the same asymmetry, suggesting a polar asymmetry of the dust to gas ratio at small distances. We compare the opacity distribution with the 3D distribution of interstellar neutral sodium resulting from the inversion of sodium columns. We discuss the similarities and discrepancies and the influence of data set limitations. Finally we discuss the potential improvements of those 3D maps.

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Pressure and Ionization Balances in the Circum-Heliospheric Interstellar Medium and the Local Bubble

Cited by 22 publications

References 77 publications

The Remarkable High Pressure of the Local Leo Cold Cloud

The Remarkable High Pressure of the Local Leo Cold Cloud

The trouble with the Local Bubble

Spatial distribution of interstellar dust in the Sun's vicinity

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