[ITAL]Far Ultraviolet Spectroscopic Explorer[/ITAL] Observations of O [CSC]vi[/CSC] Absorption in the Galactic Halo

Savage, Blair D.; Sembach, Kenneth R.; Jenkins, Edward B.; Shull, J. M.; York, Donald G.; Sonneborn, G.; Moos, H. W.; Friedman, S. D.; Green, J. C.; Oegerle, W. R.; Blair, William P.; Kruk, J. W.; Murphy, E. M.

doi:10.1086/312792

Cited by 82 publications

(59 citation statements)

References 33 publications

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“…However at present there is still no strong evidence to support any outflow of hot, ionized gas through a galactic fountain effect, and instead, halo observations of the C IV ion favor formation toward mostly negative velocities (Savage et al 1997). Interestingly, the small value of N(C IV):N(O VI) found recently for low z objects by Savage et al (2000) is best explained by a conductive heating model in which the high ions are produced mainly in isolated low halo SNRs with hot gas properties similar to those of the ten million year old Local Bubble (LB) interstellar cavity. These conclusions have been supported by the recent observations of O VI (λ1032, 1038 Å) diffuse emission recorded in the high latitude sight-line towards (l = 113…”

Section: Introductionmentioning

confidence: 83%

“…Clearly further FUSE observations are required to resolve this point, and to determine if a possible sight-line selection bias currently exists for these six observations. Absorption measurements of O VI towards high latitude sight-lines show a relatively large variation (of about an order of magnitude) in the measured O VI column density values (Savage et al 2000), such that the majority of O VI absorption probably originates in a (highly) variable contribution from the hot halo gas. However, in contrast, the relative low levels of variability in the presently determined FUSE O VI emission intensities would argue for a more local origin in which there is little contribution from halo O VI ions.…”

Section: Line-of-sight Emissionmentioning

confidence: 98%

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Far Ultraviolet Spectroscopic Explorer ($\it FUSE$) observations of emitting and absorbing gas in the Local Interstellar Chimney

Welsh

Sallmen

Sfeir

et al. 2002

A&A

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Abstract. We present Far Ultraviolet Spectroscopic Explorer (FUSE) satellite measurements of the absorption and emission characteristics of interstellar gas associated with the Local Interstellar Chimney, which is an extension of the rarefied Local Bubble cavity that extends outward from the galactic disk towards the lower galactic halo. Far ultraviolet (FUV) diffuse background emission has been detected in the high ionization line of O VI (λ1032 Å) for two lines-of-sight (l = 162.7• , b = +57.0 • ) and (l = 156.3• , b = +57.8• ) at emission levels of 2500 ± 700 photons cm −2 s −1 sr −1 (LU) and 3300 ± 1100 LU respectively. These levels of O VI emission are very similar to those found for four other lines-of-sight sampled thus far by the FUSE satellite, implying a fairly constant level of average O VI surface brightness emission at high galactic latitudes of about 2700 LU with a standard deviation of 450 LU. These emission-line data are supplemented by FUV interstellar absorption line measurements taken towards the hot DA white dwarf star, REJ 1032+532 (l = 157.5• , b = +53.2 • ), whose distance of 116 pc places it within the Local Bubble region. No high ionization interstellar O VI λ1032 Å absorption has been detected (N(O VI) < 13.0 cm −2 ), which is consistent with the non-detections of interstellar C IV and Si IV absorption reported towards this star by Holberg et al. (1999a). Taken together, our FUV absorption and emission data may be explained by a scenario in which the O VI emission and absorption lines are both formed at the conductive interface of the neutral boundary to the Local Bubble. For the presently sampled sight-lines we have found no correlation between the OVI emission line intensity and the associated 0.25 keV soft X-ray background flux as measured in the R1 and R2 bands by the ROSAT satellite. The OVI line intensities also show no correlation with the soft X-ray background flux attributable to emission from the million degree K gas of the Local Hot Bubble as modeled by Kuntz & Snowden (2000). Any (new) model of the Local Bubble must now be able to explain (i) the low levels of variability in both the O VI emission-line intensity and the associated soft X-ray background flux for galactic sight-lines >|40|• , (ii) the observed pressure of P/k ∼ 10 000 cm −3 K for the local hot interstellar gas, and (iii) the paucity of high ionization absorption lines observed within the local ISM and the sudden increase in their measured column density for distances beyond the Local Bubble neutral boundary.

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Section: Introductionmentioning

confidence: 83%

Section: Line-of-sight Emissionmentioning

confidence: 98%

Far Ultraviolet Spectroscopic Explorer ($\it FUSE$) observations of emitting and absorbing gas in the Local Interstellar Chimney

Welsh

Sallmen

Sfeir

et al. 2002

A&A

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“…Observations of the z = 0 UV O VI absorption lines are presented by several authors (e.g. Savage et al 2000;Wakker et al 2003;Indebetouw & Shull 2004;Oegerle et al 2005;Collins, Shull & Giroux 2005;Ganguly et al 2005;Savage & Lehner 2006;Bowen et al 2008;Welsh & Lallement 2008;Barstow et al 2010;Lehner et al 2011;Howk & Consiglio 2012). These probe the Galactic thin disk, thick disk, halo and the high velocity clouds, with UV O VI column densities at z = 0 ranging from ≈ 3 × 10 12 to column density observed in z = 0 systems is too small to make a detectable X-ray line, and the observed data are consistent with this expectation.…”

Section: O II Kβ "Line 12" Strength From Kαmentioning

confidence: 99%

The O vi Mystery: Mismatch between X-Ray and UV Column Densities

Mathur

Nicastro

Gupta

et al. 2017

ApJL

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The UV spectra of Galactic and extragalactic sightlines often show O VI absorption lines at a range of redshifts, and from a variety of sources from the Galactic circumgalactic medium to AGN outflows. Inner shell O VI absorption is also observed in X-ray spectra (at λ = 22.03Å), but the column density inferred from the X-ray line was consistently larger than that from the UV line. Here we present a solution to this discrepancy for the z = 0 systems. The O II Kβ line 4 S 0 → ( 3 D)3p 4 P at 562.40 eV (≡22.04Å) is blended with the O VI Kα line in X-ray spectra. We estimate the strength of this O II line in two different ways and show that in most cases the O II line accounts for the entire blended line. The small amount of O VI equivalent width present in some cases has column density entirely consistent with the UV value. This solution to the O VI discrepancy, however, does not apply to the high column density systems like AGN outflows. We discuss other possible causes to explain their UV/X-ray mismatch. The O VI and O II lines will be resolved by gratings on-board the proposed mission Arcus and the concept mission Lynx and would allow detection of weak O VI lines not just at z = 0 but also at higher redshift.

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“…Recently, FUSE has confirmed many of the overall characteristics of halo 0 VI found by ORFEUS-SPA. FUSE observations of o VI towards 11 AGNs confirm that 0 VI is more concentrated towards the galactic plane than Si IV, C IV, or N V, and that the scale height of high ions decreases with increasing ionization (Savage et al 2000; e.g., see Table 1). N(C IV)/N(O VI) ranges from ~0.15 in the disk to ~0.6 in the halo.…”

Section: Highly Ionized Gasmentioning

confidence: 85%

The interstellar medium of our Galaxy

Frisch

2001

The Century of Space Science

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Over the past century our picture of diffuse material in space has grown from a simple model of isolated clouds in thermal equilibrium with stellar radiation fields to one of a richly varied composite of materials with a wide range of physical properties and morphologies. The Solar System interacts with a dynamical interstellar medium. Optical, radio, and UV astronomy allow us to study the clouds which form the galactic environment of the Sun. The composition and distribution of interstellar clouds in the disk and halo tell us about the history of elemental formation in our galaxy, and the past and future environment of the Solar System.Dark lanes of dusty clouds obscuring portions of the Milky Way are celestial landmarks, but the realization that interstellar gas pervades space is quite recent. The twentieth century opened with the discovery of a "nebulous mass" of interstellar gas in the sightline towards the binary star 8 Orionis (Hartmann 1904). A series of over 40 spectra showed that the Ca II Kline (3933 A) absorption was nearly stationary in wavelength, "extraordinarily weak," and "almost perfectly sharp," in contrast to broader variable stellar absorption features. Sharp stationary Na I Dl and D2 lines (5890, 5896 A) were discovered in 8 Ori and f3Sco by Mary Lea Heger. An explanation offered was that a stationary absorbing cloud of vapor was present in space between these binary systems and the observer. The Ca II and Na I lines constituted the primary tracer for interstellar gas during the first half of the century.Interstellar matter (excluding dark matter) provides about 30-40% of the galactic mass density in the solar neighborhood. Trace elements heavier than He, which form the planets, record the chemical evolution of matter in our Galaxy, and provide detailed information on physical conditions in interstellar clouds, represent a small proportion of the interstellar atoms ( ~0.15%). These same elements trace

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[ITAL]Far Ultraviolet Spectroscopic Explorer[/ITAL] Observations of O [CSC]vi[/CSC] Absorption in the Galactic Halo

Cited by 82 publications

References 33 publications

Far Ultraviolet Spectroscopic Explorer ($\it FUSE$) observations of emitting and absorbing gas in the Local Interstellar Chimney

Far Ultraviolet Spectroscopic Explorer ($\it FUSE$) observations of emitting and absorbing gas in the Local Interstellar Chimney

The O vi Mystery: Mismatch between X-Ray and UV Column Densities

The interstellar medium of our Galaxy

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