The local distribution of NA I interstellar gas

Welsh, Barry Y.; Craig, N.; Vedder, P. W.; Vallerga, J. V.

doi:10.1086/175028

Cited by 69 publications

(86 citation statements)

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“…There is a 2-sigma upper limit on the intermixed H I column density within the Local Hot Bubble of N (H I) < 6.6 × 10 18 cm −2 (Juda and Bloch 1991). This limit is in agreement with the inferred average H I column density throughout the Local Cavity as derived from Na I observations along sight-lines within 60 pc (Welsh et al 1994). However, as discussed in Sect.…”

Section: 1supporting

confidence: 91%

“…This is a view looking side-on to the galaxy with the Sun at the center of the plot. Note the extension of the Local Cavity into the overlying halo via the low density Local Chimney feature, which is tilted at an angle that points towards the regions of highest soft X-ray background emission Welsh et al 1994). In a recent Na I absorption survey of 1005 sight-lines within 250 pc (Lallement et al 2003), 3-D maps of the density distribution of cold gas have revealed the Local Cavity to be an irregularly shaped rarefied region of 50-80 pc radius in most directions in the Galactic plane.…”

Section: Cool Gas Inside and Outside The Local Hot Bubblementioning

confidence: 99%

“…Other suggested Local Cavity formation scenarios involve an association with the young and massive stars of the Gould Belt (Grenier 2000) or the passage of a high velocity cloud through the galactic disk (Comeron and Torra 1994). The present day morphology of the Local Cavity seems to be defined by the 'void' within the ISM created by the outer shells of nearby overlapping superbubble structures (Welsh et al 1994;Frisch 1995). Recent modeling of the joint evolution of the Loop I and Local Hot Bubble superbubbles involve ∼ 20 SNe occurring in the moving group of OB stars of the Sco-Cen cluster which passed through the present day local cavity .…”

Section: Kinematics Of the Local Cavity Gasmentioning

confidence: 99%

“…A possible new picture of the Local Cavity is one in which it is mostly filled with a very diffuse and photoionized and/or collisionally ionized gas of temperature ∼ 20,000 K that is in rough pressure equilibrium (P /k ∼ 3000 cm −3 ) with the numerous partially ionized and warm (T ∼ 7000 K) small cloudlets that are known to exist within the LISM. The average electron density of the ionized Local Cavity 'filler gas' is assumed to be n e ∼ 0.04 cm −3 (derived from pressure equilibrium with the partially ionized LISM cloudlets) and there is also a very low average neutral gas density of n(H) < 0.01 cm −3 within the Local Cavity (Dupin and Gry 1998;Welsh et al 1994). We note that there may also be a contribution from magnetic pressure such that the total pressure of both the local interstellar cloud and 'filler gas' may be higher than we have assumed.…”

Section: The 'Hot Top Model'mentioning

confidence: 99%

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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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Section: 1supporting

confidence: 91%

Section: Cool Gas Inside and Outside The Local Hot Bubblementioning

confidence: 99%

Section: Kinematics Of the Local Cavity Gasmentioning

confidence: 99%

Section: The 'Hot Top Model'mentioning

confidence: 99%

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The trouble with the Local Bubble

Welsh

Shelton

2009

Astrophys Space Sci

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“…The distribution of the local interstellar medium has been the subject of extensive studies, mostly based on the measurement of the NaID doublet at 5890Å (Welsh et al 1994;Sfeir et al 1999). Our current environment is rather unusual since we appear to be located in a local bubble cavity of very low interstellar gas density.…”

Section: Discussionmentioning

confidence: 99%

Measuring proper motions of isolated neutron stars with Chandra

Motch

Pires

Haberl

et al. 2007

Isolated Neutron Stars: From the Surface to the Interior

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The excellent spatial resolution of the Chandra observatory offers the unprecedented possibility to measure proper motions at X-ray wavelength with relatively high accuracy using as reference the background of extragalactic or remote galactic X-ray sources. We took advantage of this capability to constrain the proper motion of RX J0806.4−4123 and RX J0420.0−5022, two Xray bright and radio quiet isolated neutron stars (INSs) discovered by ROSAT and lacking an optical counterpart. In this paper, we present results from a preliminary analysis from which we derive 2σ upper limits of 76 mas/yr and 138 mas/yr on the proper motions of RX J0806.4−4123 and RX J0420.0−5022 respectively. We use these values together with those of other ROSAT discovered INSs to constrain the origin, distance and evolutionary status of this particular group of objects. We find that the tangential velocities of radio quiet ROSAT neutron stars are probably consistent with those of 'normal' pulsars. Their distribution on the sky and, for those having accurate proper motion vectors, their possible birth places, all point to a local population, probably created in the part of the Gould Belt nearest to the earth.

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White Dwarf Circumstellar Disks: Observations

Farihi¹

2011

White Dwarf Atmospheres and Circumstellar Environments

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The local distribution of NA I interstellar gas

Cited by 69 publications

References 0 publications

The trouble with the Local Bubble

The trouble with the Local Bubble

Measuring proper motions of isolated neutron stars with Chandra

White Dwarf Circumstellar Disks: Observations

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