Heating and Ionization of HI Regions

Dalgarno, A.; McCray, Richard

doi:10.1146/annurev.aa.10.090172.002111

Cited by 798 publications

(658 citation statements)

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“…A subsequent observation with the COS G140L grating shows unambiguous emission lines from both C iv and the He ii (Sparks et al 2012), indicating the presence of 10 5 K gas in these structures. At lower temperatures, Werner et al (2013) used the PACS instrument on Herschel to detect [C ii] λ158µm emission from M87 which seems to trace the filamentary structure as well; this is typically the dominant cooling line when Hydrogen is neutral (Dalgarno & McCray 1972) and is most effective at temperatures around 10 2 K.…”

Section: M87 Filamentmentioning

confidence: 99%

Searching for FUV line emission from 10⁷ K gas in massive elliptical galaxies and galaxy clusters as a tracer of turbulent velocities

Anderson

Sunyaev

2016

Mon. Not. R. Astron. Soc.

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Non-thermal pressure from turbulence and bulk flows is a fundamental ingredient in hot gaseous halos, and in the intracluster medium it will be measured through emission line kinematics with calorimeters on future X-ray spacecraft. In this paper we present a complementary method for measuring these effects, using forbidden FUV emission lines of highly ionized Iron which trace 10 7 K gas. The brightest of these is [Fe xxi] λ1354.1. We search for these lines in archival HST-COS spectra from the well-known elliptical galaxies M87 and NGC4696, which harbor large reservoirs of 10 7 K gas. We report a 2.2σ feature which we attribute to [Fe xxi] from a filament in M87, and positive residuals in the nuclei of M87 and NGC4696, for which the 90% upper limits on the line flux are close to the predicted fluxes based on X-ray observations. In a newer reduction of the data from the Hubble Spectroscopic Legacy Archive, these limits become tighter and the [Fe xxi] feature reaches a formal significance of 5.3σ, neglecting uncertainty in fitting the continuum. Using our constraints, we perform emission measure analysis, constraining the characteristic path length and column density of the ∼ 10 7 K gas. We also examine several sightlines towards filaments or cooling flows in other galaxy clusters, for which the fraction of gas at 10 7 K is unknown, and place upper limits on its emission measure in each case. A mediumresolution HST-COS observation of the M87 filament for ∼10 orbits would confirm our detection of [Fe xxi] and measure its width.

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Section: M87 Filamentmentioning

confidence: 99%

Searching for FUV line emission from 10⁷ K gas in massive elliptical galaxies and galaxy clusters as a tracer of turbulent velocities

Anderson

Sunyaev

2016

Mon. Not. R. Astron. Soc.

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“…The present model introduces substantial improvements to that of Avillez (2000), namely: (i) inclusion of background heating due to starlight varying with z (Wolfire et al 1995) and kept constant in the directions parallel to the Galactic plane (z = 0) where it is chosen to initially balance radiative cooling at 9000 K. With the inclusion of background heating the gas at T < 10 4 K becomes thermally bistable; (ii) use of a tabulated cooling function taken from Dalgarno & McCray (1972) with an ionization fraction of 0.1 at temperatures below 10 4 K and a temperature cutoff at 10 K; (iii) inclusion of SNe type Ia with a scale height of 325 pc (Freeman 1987); (iv) OB stars form in regions with a density and temperature thresholds of 10 cm −3 and 100 K, respectively, and their number, masses and main sequence life times τ MS are determined from the initial mass function. Roughly sixty percent of the OB stars explode within the cluster, while the remaining (composed of the lowest mass stars whose location is determined kinematically by attributing to each star a random direction and a velocity) explode in the field with a scale height of 90 pc.…”

Section: Setup Of Basic Processesmentioning

confidence: 99%

Volume filling factors of the ISM phases in star forming galaxies

Avillez¹,

Breitschwerdt²

2004

A&A

182

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Abstract. The role of matter circulation between the disk and halo in establishing the volume filling factors of the different ISM phases in the Galactic disk (|z| ≤ 250 pc) is investigated, using a modified version of the three-dimensional supernovadriven ISM model of Avillez (2000). We carried out adaptive mesh refinement simulations of the ISM with five supernova rates (in units of the Galactic value), σ/σ Gal = 1, 2, 4, 8 and 16 (corresponding to starburst conditions) using three finer level resolutions of 2.5, 1.25 and 0.625 pc, allowing us to understand how resolution would affect the volumes of gas phases in pressure equilibrium. We find that the volume filling factors of the different ISM phases depend sensitively on the existence of a duty cycle between the disk and halo acting as a pressure release valve for the hot (T > 10 5.5 K) phase in the disk. The amount of cold gas (defined as the gas with T < 10 3 K) picked up in the simulations varies from a value of 19% for σ/σ Gal = 1 to ∼5% for σ/σ Gal = 4 and ≤1% for higher SN rates. Background heating prevents the cold gas from immediate collapse and thus ensures the stability of the cold gas phase. The mean occupation fraction of the hot phase varies from about 17% for the Galactic SN rate to ∼28%, for σ/σ Gal = 4, and to 44% for σ/σ Gal = 16. Overall the filling factor of the hot gas does not increase much as we move towards higher SN rates, following a power law of f v, hot ∝ (σ/σ Gal ) 0.363 . Such a modest dependence on the SN rate is a consequence of the evacuation of the hot phase into the halo through the duty cycle. This leads to volume filling factors of the hot phase considerably smaller than those predicted in the three-phase model of McKee & Ostriker (1977) even in the absence of magnetic fields.

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“…The gas is cooled by thermal excitation and subsequent re-radiation of energy by CI, CII, OI, FeII, and SII via line emission at infrared wavelengths as discussed by Dalgarno & McCray (1972). Quadrupole radiation produced by the J = 2 → 0 H 2 rotational transition is also considered as a cooling process, as are various vibrational-rotational transitions considered by Hartquist, Oppenheimer, & Dalgarno (1980).…”

Section: Uv(t)mentioning

confidence: 99%

Molecular photodissociation in the neutral envelopes of planetary nebulae

Gussie¹,

Taylor²,

Dewdney³

et al. 1995

Monthly Notices of the Royal Astronomical Society

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The dissociation and subsequent ionisation of molecular material in a detached, spherically symmetric stellar wind is modelled as a star evolves from the post-asymptotic giant branch phase to a planetary nebula (i.e. from a stellar effective temperature of T eff = 6000 K to T eff = 33000 K). The model is compared to the observed mass and distribution of ionised and atomic hydrogen in the planetary nebula IC 418. It is found that the mass of circumnebular atomic hydrogen observed in IC 418. can easily be produced by the dissociation of originally molecular material by the ultraviolet radiation of the central star. However, the observed spatial distribution of the gas is not accurately recreated by the current model.

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Heating and Ionization of HI Regions

Cited by 798 publications

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Searching for FUV line emission from 10⁷ K gas in massive elliptical galaxies and galaxy clusters as a tracer of turbulent velocities

Searching for FUV line emission from 10⁷ K gas in massive elliptical galaxies and galaxy clusters as a tracer of turbulent velocities

Volume filling factors of the ISM phases in star forming galaxies

Molecular photodissociation in the neutral envelopes of planetary nebulae

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Heating and Ionization of HI Regions

Cited by 798 publications

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Searching for FUV line emission from 107 K gas in massive elliptical galaxies and galaxy clusters as a tracer of turbulent velocities

Searching for FUV line emission from 107 K gas in massive elliptical galaxies and galaxy clusters as a tracer of turbulent velocities

Volume filling factors of the ISM phases in star forming galaxies

Molecular photodissociation in the neutral envelopes of planetary nebulae

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Searching for FUV line emission from 10⁷ K gas in massive elliptical galaxies and galaxy clusters as a tracer of turbulent velocities

Searching for FUV line emission from 10⁷ K gas in massive elliptical galaxies and galaxy clusters as a tracer of turbulent velocities