High-resolution observations of interstellar Na i and Ca ii towards the southern opening of the ‘Local Interstellar Chimney’: probing the disc—halo connection

Crawford, Ian; Lallement, R.; Price, Richard J.; Sfeir, D.; Wakker, B. P.; Welsh, Barry Y.

doi:10.1046/j.1365-8711.2002.05959.x

Cited by 29 publications

(24 citation statements)

References 54 publications

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“…To study the degree of dust depletion in the absorbers, the N Na i /N Ca ii ratio has often been used as a probe (Welsh et al 1990;Bertin et al 1993;Crawford et al 2002;Kondo et al 2006), because sodium is hardly depleted onto grains while calcium can be strongly depleted (Savage & Sembach 1996).…”

Section: Possible Association With Known Ivc or Hvc Complexesmentioning

confidence: 99%

An absorption-selected survey of neutral gas in the Milky Way halo

Bekhti

Winkel

Richter

et al. 2012

A&A

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Aims. We aim at analysing systematically the distribution and physical properties of neutral and mildly ionised gas in the Milky Way halo, based on a large absorption-selected data set. Methods.Multi-wavelength studies were performed combining optical absorption line data of Ca ii and Na i with follow-up H i 21-cm emission line observations along 408 sight lines towards low-and high-redshift QSOs. We made use of archival optical spectra obtained with UVES/VLT. H i data were extracted from the Effelsberg-Bonn H i survey and the Galactic All-Sky survey.For selected sight lines we obtained deeper follow-up observations using the Effelsberg 100-m telescope.Results. Ca ii (Na i) halo absorbers at intermediate and high radial velocities are present in 40-55% (20-35%) of the sightlines, depending on the column density threshold chosen. Many halo absorbers show multi-component absorption lines, indicating the presence of sub-structure. In 65% of the cases, absorption is associated with H i 21-cm emission. The Ca ii (Na i) column density distribution function follows a power-law with a slope of β ≈ −2.2 (−1.4). Conclusions. Our absorption-selected survey confirms our previous results that the Milky Way halo is filled with a large number of neutral gas structures whose high column density tail represents the population of common H i high-and intermediate-velocity clouds seen in 21-cm observations. We find that Na i/Ca ii column density ratios in the halo absorbers are typically smaller than those in the Milky Way disc, in the gas in the Magellanic Clouds, and in damped Lyman α systems. The small ratios (prominent in particular in high-velocity components) indicate a lower level of Ca depletion onto dust grains in Milky Way halo absorbers compared to gas in discs and inner regions of galaxies.

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Section: Possible Association With Known Ivc or Hvc Complexesmentioning

confidence: 99%

An absorption-selected survey of neutral gas in the Milky Way halo

Bekhti

Winkel

Richter

et al. 2012

A&A

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“…5 clearly shows the significant elongation of the low density LB cavity extending at least to a distance of >250 pc into the lower inner-halo regions of both galactic hemispheres. This interstellar feature has been termed the "Local Chimney" (LC) by Welsh et al (1999) and the physical state of the gas in this low-density sight-line has been the focus of two recent interstellar studies by Crawford et al (2002) and . As yet, no distinct and continuous neutral boundary to the ends of the LC has been found in either galactic hemisphere for distances <400 pc, and Crawford et al (2002) favor a picture of the inner galactic halo (in the southern hemisphere) in which a population of scattered, generally infalling, discrete diffuse clouds lie along the LC sight-line.…”

Section: The Lism Viewed In the Meridian Plane -Figmentioning

confidence: 99%

3D mapping of the dense interstellar gas around the Local Bubble

Lallement

Welsh

Vergely

et al. 2003

A&A

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Abstract. We present intermediate results from a long-term program of mapping the neutral absorption characteristics of the local interstellar medium, motivated by the availability of accurate and consistent parallaxes from the Hipparcos satellite. Equivalent widths of the interstellar NaI D-line doublet at 5890 Å are presented for the lines-of-sight towards some 311 new target stars lying within ∼350 pc of the Sun. Using these data, together with NaI absorption measurements towards a further ∼240 nearby targets published in the literature (for many of them, in the directions of molecular clouds), and the ∼450 linesof-sight already presented by , we show 3D absorption maps of the local distribution of neutral gas towards 1005 sight-lines with Hipparcos distances as viewed from a variety of different galactic projections. The data are synthesized by means of two complementary methods, (i) by mapping of iso-equivalent width contours, and (ii) by density distribution calculation from the inversion of column-densities, a method devised by Vergely et al. (2001). Our present data confirms the view that the local cavity is deficient in cold and neutral interstellar gas. The closest dense and cold gas "wall", in the first quadrant, is at ∼55-60 pc. There are a few isolated clouds at closer distance, if the detected absorption is not produced by circumstellar material. The maps reveal narrow or wide "interstellar tunnels" which connect the Local Bubble to surrounding cavities, as predicted by the model of Cox & Smith (1974). In particular, one of these tunnels, defined by stars at 300 to 600 pc from the Sun showing negligible sodium absorption, connects the well known CMa void , which is part of the Local Bubble, with the supershell GSH 238+00+09 (Heiles 1998). High latitude lines-of-sight with the smallest absorption are found in two "chimneys", whose directions are perpendicular to the Gould belt plane. The maps show that the Local Bubble is "squeezed" by surrounding shells in a complicated pattern and suggest that its pressure is smaller than in those expanding regions. We discuss the locations of several HI and molecular clouds. Using comparisons between NaI and HI or CO velocities, in some cases we are able to improve the constraints on their distances. According to the velocity criteria, MBM 33−37, MBM 16−18, UT 3−7, and MBM 54−55 are closer than ∼100 pc, and MBM 40 is closer than 80 pc. Dense HI clouds are seen at less than 90 pc and 85 pc in the directions of the MBM 12 and MBM 41−43 clouds respectively, but the molecular clouds themselves may be far beyond. The above closest molecular clouds are located at the neutral boundary of the Bubble. Only one translucent cloud, G192−67, is clearly embedded within the LB and well isolated. These maps of the distribution of local neutral interstellar NaI gas are also briefly compared with the distribution of both interstellar dust and neutral HI gas within 300 pc.

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“…It was first noted by Welsh et al (1999) that the angle of the Local Chimney is tilted towards the directions where the SXRB emission is greatest in both galactic hemispheres. The absorption characteristics of gas lying close to the axis of the Chimney have been probed by Crawford et al (2002) and Welsh, Sallmen & Lallement (2004). These observations show that interstellar gas with velocities in the -20 to -60 km/s range appears to be falling down the Chimney towards the galactic disk.…”

Section: Towards An Understanding Of the O Vi-sxrbmentioning

confidence: 99%

O VI in the local interstellar medium

Barstow¹,

Boyce²,

Barstow³

et al. 2008

Space Astronomy

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We report the results of a search for O VI absorption in the spectra of 80 hot DA white dwarfs observed by the FUSE satellite. We have carried out a detailed analysis of the radial velocities of interstellar and (where present) stellar absorption lines for the entire sample of stars. In approximately 35% of cases (where photospheric material is detected), the velocity differences between the interstellar and photospheric components were beneath the resolution of the FUSE spectrographs. Therefore, in 65% of these stars the interstellar and photospheric contributions could be separated and the nature of the O VI component unambiguously determined. Furthermore, in other examples, where the spectra were of a high signal-to-noise, no photospheric material was found and any O VI detected was assumed to be interstellar. Building on the earlier work of Oegerle et al. (2005) and Savage & Lehner (2006), we have increased the number of detections of interstellar O VI and, for the first time, compared their locations with both the soft X-ray background emission and new detailed maps of the distribution of neutral gas within the local interstellar medium. We find no strong evidence to support a spatial correlation between O VI and SXRB emission. In all but a few cases, the interstellar O VI was located at or beyond the boundaries of the local cavity. Hence, any T ~ 300,000K gas responsible for the O VI absorption may reside at the interface between the cavity and surrounding medium or in that medium itself. Consequently, it appears that there is much less O VI-bearing gas than previously stated within the inner rarefied regions of the local interstellar cavity.

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High-resolution observations of interstellar Na i and Ca ii towards the southern opening of the ‘Local Interstellar Chimney’: probing the disc—halo connection

Cited by 29 publications

References 54 publications

An absorption-selected survey of neutral gas in the Milky Way halo

An absorption-selected survey of neutral gas in the Milky Way halo

3D mapping of the dense interstellar gas around the Local Bubble

O VI in the local interstellar medium

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