Line integrals of N[SUB]E[/SUB] and (n[SUB]E)-squared[/SUB] at high Galactic latitude

Reynolds, R. J.

doi:10.1086/186013

Cited by 138 publications

(130 citation statements)

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“…The warm gas detected in Hα emission at the disk-halo interface is referred to as the Reynolds or warm ionized medium (WIM) layer (Haffner et al, 2003;Reynolds, 1993). This is a layer of warm gas extending ∼ 2 kpc above the disk with a volume averaged density of 0.01 − 0.1 cm −3 and a filling factor of > 30% at 1-1.5 kpc (Reynolds, 1991;Gaensler et al, 2008;Haffner et al, 2009). As illustrated in Figure 5, at lower z-heights more of the volume is filled in with HI and at higher z-heights the hot gas fills more of the volume Gaensler et al, 2008).…”

Section: The Disk-halo Interfacementioning

confidence: 99%

Gaseous Galaxy Halos

Putman

Peek

Joung

2012

Annu. Rev. Astron. Astrophys.

464

479

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Galactic halo gas traces inflowing star formation fuel and feedback from a galaxy's disk and is therefore crucial to our understanding of galaxy evolution. In this review, we summarize the multi-wavelength observational properties and origin models of Galactic and low redshift spiral galaxy halo gas. Galactic halos contain multiphase gas flows that are dominated in mass by the ionized component and extend to large radii. The densest, coldest halo gas observed in neutral hydrogen (HI) is generally closest to the disk (< 20 kpc), and absorption line results indicate warm and warm-hot diffuse halo gas is present throughout a galaxy's halo. The hot halo gas detected is not a significant fraction of a galaxy's baryons. The disk-halo interface is where the multiphase flows are integrated into the star forming disk, and there is evidence for both feedback and fueling at this interface from the temperature and kinematic gradient of the gas and HI structures. The origin and fate of halo gas is considered in the context of cosmological and idealized local simulations. Accretion along cosmic filaments occurs in both a hot (> 10 5.5 K) and cold mode in simulations, with the compressed material close to the disk the coldest and densest, in agreement with observations. There is evidence in halo gas observations for radiative and mechanical feedback mechanisms, including escaping photons from the disk, supernova-driven winds, and a galactic fountain. Satellite accretion also leaves behind abundant halo gas. This satellite gas interacts with the existing halo medium, and much of this gas will become part of the diffuse halo before it can reach the disk. The accretion rate from cold and warm halo gas is generally below a galaxy disk's star formation rate, but gas at the disk-halo interface and stellar feedback may be important additional fuel sources.

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Section: The Disk-halo Interfacementioning

confidence: 99%

Gaseous Galaxy Halos

Putman

Peek

Joung

2012

Annu. Rev. Astron. Astrophys.

464

479

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“…n 0 , DM 0 , H n , H n 2 , H N and H f ) will be unchanged. For the sake of completeness and for comparison with previous studies, we also compute the vertical 'occupation length', L c ≡ (DM 0 ) 2 /EM 0 , and 'characteristic density', N c ≡ EM 0 /DM 0 , of the WIM (Reynolds 1991a;Hill et al 2008). For DM 0 ≈ 26.0 pc cm −3 and EM 0 ≈ 1.9 pc cm −6 as derived above, we find L c ≈ 350 pc and N c ≈ 0.07 cm −3 .…”

Section: The Filling Factor Of Ionised Gasmentioning

confidence: 99%

The Vertical Structure of Warm Ionised Gas in the Milky Way

Gaensler

Madsen

Chatterjee

et al. 2008

Publ. – Astron. Soc. Aust

312

400

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We present a new joint analysis of pulsar dispersion measures and diffuse Hα emission in the Milky Way, which we use to derive the density, pressure and filling factor of the thick disk component of the warm ionised medium (WIM) as a function of height above the Galactic disk. By excluding sightlines at low Galactic latitude that are contaminated by Hii regions and spiral arms, we find that the exponential scale-height of free electrons in the diffuse WIM is 1830 +120 −250 pc, a factor of two larger than has been derived in previous studies. The corresponding inconsistent scale heights for dispersion measure and emission measure imply that the vertical profiles of mass and pressure in the WIM are decoupled, and that the filling factor of WIM clouds is a geometric response to the competing environmental influences of thermal and non-thermal processes. Extrapolating the properties of the thick-disk WIM to mid-plane, we infer a volume-averaged electron density 0.014 ± 0.001 cm −3 , produced by clouds of typical electron density 0.34 ± 0.06 cm −3 with a volume filling factor 0.04 ± 0.01. As one moves off the plane, the filling factor increases to a maximum of ∼30% at a height of ≈1-1.5 kpc, before then declining to accommodate the increasing presence of hot, coronal gas. Since models for the WIM with a ≈1 kpc scale-height have been widely used to estimate distances to radio pulsars, our revised parameters suggest that the distances to many high-latitude pulsars have been substantially underestimated.

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“…. 0.2 in the disk (Reynolds 1991), models assuming clumping on a scale below the grid-resolution are still unsatisfactory with regard to exploring the supply of ionizing photons to the DIG. This is because this sort of "microclumping" -where the clumps are assumed to be so small that they remain optically thin -will primarily enhance the recombination rate and thus yield geometrically smaller Strömgren spheres for a given mean density (although of course the ionization balance of the metals will be analogously affected, leading to possibly different emission line strength ratios).…”

Section: Synthetic Spectramentioning

confidence: 99%

Numerical models for the diffuse ionized gas in galaxies

Hoffmann¹,

Lieb²,

Pauldrach³

et al. 2012

A&A

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Aims. The aim of this work is to verify whether turbulent magnetic reconnection can provide the additional energy input required to explain the up to now only poorly understood ionization mechanism of the diffuse ionized gas (DIG) in galaxies and its observed emission line spectra. Methods. We use a detailed non-LTE radiative transfer code that does not make use of the usual restrictive gaseous nebula approximations to compute synthetic spectra for gas at low densities. Excitation of the gas is via an additional heating term in the energy balance as well as by photoionization. Numerical values for this heating term are derived from three-dimensional resistive magnetohydrodynamic two-fluid plasma-neutral-gas simulations to compute energy dissipation rates for the DIG under typical conditions. Results. Our simulations show that magnetic reconnection can liberate enough energy to by itself fully or partially ionize the gas. However, synthetic spectra from purely thermally excited gas are incompatible with the observed spectra; a photoionization source must additionally be present to establish the correct (observed) ionization balance in the gas.

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Line integrals of N[SUB]E[/SUB] and (n[SUB]E)-squared[/SUB] at high Galactic latitude

Cited by 138 publications

References 0 publications

Gaseous Galaxy Halos

Gaseous Galaxy Halos

The Vertical Structure of Warm Ionised Gas in the Milky Way

Numerical models for the diffuse ionized gas in galaxies

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