Highly ionized gas in the local ISM: Some like it hot?

Welsh, Barry Y.; Lallement, R.

doi:10.1051/0004-6361:20042611

Cited by 39 publications

(47 citation statements)

References 56 publications

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“…However, a handful of interstellar N v components with narrower b-values have been found, in sight lines passing through supershells Savage et al 2001) and the Local Interstellar Medium (Welsh & Lallement 2005). Thus N v behaves similarly in high-z DLAs as in the Milky Way, with each case showing a majority of broad components and a minority of narrow components.…”

Section: The N V Detection Rate In Dlasmentioning

confidence: 94%

Metal-enriched plasma in protogalactic halos

Fox¹,

Prochaska

Ledoux³

et al. 2009

A&A

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We continue our recent work of characterizing the plasma content of high-redshift damped and sub-damped Lyman-α systems (DLAs/sub-DLAs), which represent multi-phase gaseous (proto)galactic disks and halos seen toward a background source. We survey N v absorption in a sample of 91 DLAs and 18 sub-DLAs in the redshift range 1.67 < z abs < 4.28 with unblended coverage of the N v doublet. Our dataset includes high-resolution (6−8 km s are required to keep the cloud sizes physically reasonable. The nature of the remaining ≈80% of (broad) N v components is unclear; models of radiatively-cooling collisionally-ionized plasma at log (T /K) = 5.2−5.4 are fairly successful in reproducing the observed integrated high-ion column density ratios and the component line widths, but we cannot rule out photoionization by local sources.Finally, we identify several unusual DLAs with extremely low metallicity (<0.01 solar) but strong high-ion absorption (log N(N v) > 14 or log N(O vi) > 14.2), which present challenges to either galactic inflow or outflow models.

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Section: The N V Detection Rate In Dlasmentioning

confidence: 94%

Metal-enriched plasma in protogalactic halos

Fox¹,

Prochaska

Ledoux³

et al. 2009

A&A

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“…the ScoCen association). This inflow has been traced using both low (Ca II, S II, Fe II) and high ionization (C IV, Si IV, N V) species, all of which possess significant negative velocity motions for sight-lines of distance > 90 pc in the general direction of l = 330 • , b = +18 • (Welsh and Lallement 2005). Secondly, for galactic directions close to the axis of the Local Chimney that extend into the lower halo, interstellar gas clouds with inflow velocities in the −20 to −60 km/s range have been detected along sight-lines spanning both open-ends of the Local Chimney which appear to be falling towards the galactic disk (Welsh et al 2004;Crawford et al 2002).…”

Section: Kinematics Of the Local Cavity 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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“…Lallement et al 1995;Redfield & Linsky 2008;Welsh & Lallement 2005) and the strong NaI and CaII interstellar in the visible (e.g. Genova & Beckman 2003;Snow et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Spatial distribution of interstellar dust in the Sun's vicinity

Vergely¹,

Valette

Lallement

et al. 2010

A&A

Self Cite

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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Highly ionized gas in the local ISM: Some like it hot?

Cited by 39 publications

References 56 publications

Metal-enriched plasma in protogalactic halos

Metal-enriched plasma in protogalactic halos

The trouble with the Local Bubble

Spatial distribution of interstellar dust in the Sun's vicinity

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