Diffuse Ionised Gas in Edge-on Galaxies

Rand, Richard J.

doi:10.1071/as98106

Cited by 18 publications

(13 citation statements)

References 35 publications

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“…Such emission is found in several other spirals as well [142,143,127,128]. In the Galaxy, the Reynolds layer contains a substantial portion of the H + in the ISM.…”

Section: Heating Of Diffuse Ionized Gasmentioning

confidence: 96%

MHD Turbulence: Scaling Laws and Astrophysical Implications

Cho

Lazarían

Vishniac

2003

Turbulence and Magnetic Fields in Astrophysics

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Abstract. Turbulence is the most common state of astrophysical flows. In typical astrophysical fluids, turbulence is accompanied by strong magnetic fields, which has a large impact on the dynamics of the turbulent cascade. Recently, there has been a significant breakthrough on the theory of magnetohydrodynamic (MHD) turbulence. For the first time we have a scaling model that is supported by both observations and numerical simulations. We review recent progress in studies of both incompressible and compressible turbulence. We compare Iroshnikov-Kraichnan and Goldreich-Sridhar models, and discuss scalings of Alfvén, slow, and fast waves. We also discuss the completely new regime of MHD turbulence that happens below the scale at which hydrodynamic turbulent motions are damped by viscosity. In the case of the partially ionized diffuse interstellar gas the viscosity is due to neutrals and truncates the turbulent cascade at ∼parsec scales. We show that below this scale magnetic fluctuations with a shallow spectrum persist and discuss the possibility of a resumption of the MHD cascade after ions and neutrals decouple. We discuss the implications of this new insight into MHD turbulence for cosmic ray transport, grain dynamics, etc., and how to test theoretical predictions against observations.

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“…Such emission is found in several other spirals as well [142,143,127,128]. In the Galaxy, the Reynolds layer contains a substantial portion of the H + in the ISM.…”

Section: Heating Of Diffuse Ionized Gasmentioning

confidence: 96%

MHD Turbulence: Scaling Laws and Astrophysical Implications

Cho

Lazarían

Vishniac

2003

Turbulence and Magnetic Fields in Astrophysics

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“…The DIG has a different emission-line spectrum to starforming regions. The escaped hard radiation field produces strong emission in low-ionization species, such as [O I], [N II], [C II], and [S II], but weak emission in high ionization species such as [O III] (see reviews by Rand 1998;Mathis 2000;Haffner et al 2009). The DIG may contribute between 10-50% of the Hα emission, but may contaminate the [N II], [S II] and other low ionization lines up to 2-3× more (Madsen et al 2006;Oey et al 2007;Blanc et al 2009).…”

Section: Diffuse Ionized Gasmentioning

confidence: 99%

Theoretical ISM Pressure and Electron Density Diagnostics for Local and High-redshift Galaxies

Kewley

Nicholls

Sutherland

et al. 2019

ApJ

114

129

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We derive new self-consistent theoretical UV, optical, and IR diagnostics for the ISM pressure and electron density in the ionized nebulae of star-forming galaxies. Our UV diagnostics utilize the intercombination, forbidden and resonance lines of silicon, carbon, aluminum, neon, and nitrogen. We also calibrate the optical and IR forbidden lines of oxygen, argon, nitrogen and sulfur. We show that line ratios used as ISM pressure diagnostics depend on the gas-phase metallicity with a residual dependence on the ionization parameter of the gas. In addition, the traditional electron density diagnostic [S II] λ6731/[S II] λ6717 is strongly dependent on the gas-phase metallicity. We show how different emission-line ratios are produced in different ionization zones in our theoretical nebulae. The [S II] and [O II] ratios are produced in different zones, and should not be used interchangeably to measure the electron density of the gas unless the electron temperature is known to be constant. We review the temperature and density distributions observed within H II regions and discuss the implications of these distributions on measuring the electron density of the gas. Many H II regions contain radial variations in density. We suggest that the ISM pressure is a more meaningful quantity to measure in H II regions or galaxies. Specific combinations of line ratios can cover the full range of ISM pressures (4 < log(P/k) < 9). As H II regions become resolved at increasingly high redshift through the next generation telescopes, we anticipate that these diagnostics will be important for understanding the conditions around the young, hot stars from the early universe to the present day.

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“…galaxies from Rand (1998) and the correlation with extraplanar diffuse ionized gas, one can see that M101 is not expected to have a very extended '' DIG '' layer. This is not to say that star formation in M101 is in any way '' quiescent ''; the several giant H ii regions are more reminiscent of those in the Magellanic Clouds than the star-forming regions seen in the Milky Way.…”

Section: No 1 2003 Diffuse X-ray Emission From M101mentioning

confidence: 99%

Diffuse X‐Ray Emission from M101

Küntz

Snowden

Pence

et al. 2003

ApJ

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The total 0.45-1.0 keV luminosity of M101 is 3:2 Â 10 39 ergs s À1 , of which 2:3 Â 10 39 ergs s À1 is due to diffuse emission. (Chandra observes only $60% of the diffuse emission observed by ROSAT because of its superior point-source detection.) Of the diffuse emission seen by Chandra, no more than 6% can be due to luminous unresolved point sources, such as X-ray binaries, and $10% is likely due to dwarf stars. The diffuse emission traces the spiral arms and is roughly correlated with the H and far-UV emission. The radial distribution closely follows the optical profile. The bulk of the diffuse emission is characterized by a two-thermal component spectrum with kT ¼ 0:20 and 0.75 keV, and the ratio of the emission measures of the two components is roughly constant as a function of both radius and surface brightness. The softer component has a sufficiently large covering factor that the bulk of the emission is likely extraplanar. We find no evidence of an extended axisymmetric X-ray halo, suggesting that any such halo has a strength much smaller than current predictions.

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Diffuse Ionised Gas in Edge-on Galaxies

Cited by 18 publications

References 35 publications

MHD Turbulence: Scaling Laws and Astrophysical Implications

MHD Turbulence: Scaling Laws and Astrophysical Implications

Theoretical ISM Pressure and Electron Density Diagnostics for Local and High-redshift Galaxies

Diffuse X‐Ray Emission from M101

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