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Böhringer, Hannes

doi:10.30965/9783846749661_015

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“…Calculations of the cooling rates of astrophysical plasma in the collisional ionization equilibrium (CIE) were performed by many authors (House 1964; Cox & Tucker 1969; Raymond, Cox & Smith 1976; Shull & van Steenberg 1982; Gaetz & Salpeter 1983; Böhringer & Hensler 1989; Sutherland & Dopita 1993; Landi & Landini 1999; Benjamin, Benson & Cox 2001; Bryans et al 2006). However, calculations of the time‐dependent ionization of metals and associated radiative cooling showed significant deviations from the CIE states (Kafatos 1973; Shapiro & Moore 1976; Edgar & Chevalier 1986; Schmutzler & Tscharnuter 1993; Sutherland & Dopita 1993; Gnat & Sternberg 2007).…”

Section: Introductionmentioning

confidence: 99%

Non-equilibrium ionization states and cooling rates of photoionized enriched gas

Vasiliev¹

2011

Monthly Notices of the Royal Astronomical Society

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Non-equilibrium (time-dependent) cooling rates and ionization state calculations are presented for low-density gas enriched with heavy elements (metals) and photoionized by external ultraviolet/X-ray radiation. We consider a wide range of gas densities and metallicities and also two types of external radiation field: a power-law and an extragalactic background spectra. We have found that both cooling efficiencies and ionic composition of enriched photoionized gas depend significantly on the gas metallicity and density, the flux amplitude and the shape of ionizing radiation spectrum. The cooling rates and ionic composition of the gas in non-equilibrium photoionization models differ strongly (by a factor of several) from those in photoequilibrium due to overionization of the ionic states in the non-equilibrium case. The difference is maximal at low values of the ionization parameter and similar in magnitude to that between the equilibrium and non-equilibrium cooling rates in the collisionally controlled gas. In general, the non-equilibrium effects are notable at T 10 6 K. In this temperature range, the extent of mismatch between the two ionic states and their ratios between the photoequilibrium and the photo-non-equilibrium models reach a factor of several. The net result is that the time-dependent energy losses due to each chemical element (i.e. the contributions to the total cooling rate) differ significantly from the photoequilibrium ones. We advocate the use of non-equilibrium cooling rates and ionic states for gas with near-solar (and above) metallicity exposed to an arbitrary ionizing radiation flux. We provide a parameter space (in terms of temperature, density, metallicity and ionizing radiation flux), where the non-equilibrium cooling rates are to be used. More quantitatively, the non-equilibrium collisional cooling rates and ionization states are a better choice for the ionization parameter log U −5. The difference between the photoequilibrium and the photo-non-equilibrium decreases with the ionization parameter growth, and the photoequilibrium can be used for ionization parameter as high as log U −2 for Z 10 −2 Z and log U 0 for Z ∼ Z . Thus, the non-equilibrium calculations should be used for the ionization parameter range between the above-mentioned values. In general, where the physical conditions favour collisional ionization, the non-equilibrium (photo)ionization calculations should be conducted.

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Section: Introductionmentioning

confidence: 99%

Non-equilibrium ionization states and cooling rates of photoionized enriched gas

Vasiliev¹

2011

Monthly Notices of the Royal Astronomical Society

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Cited by 1 publication

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Non-equilibrium ionization states and cooling rates of photoionized enriched gas

Non-equilibrium ionization states and cooling rates of photoionized enriched gas

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