Secondary ionization and heating by fast electrons
Secondary ionization and heating by fast electrons
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快速电子的二次电离和加热
DOI：
10.1111/j.1365-2966.2010.16401.x
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发表时间：
2009
影响因子：
4.8
通讯作者：
Samuel Johnson Stoever
中科院分区：
文献类型：
--
作者：
S. Furlanetto;Samuel Johnson Stoever
我们研究了在原始组成的热气体中快速电子（能量为ebbb10 eV）的命运。为了跟踪它们与背景气体的相互作用，我们构建了一个蒙特卡罗模型，该模型包括：(1)电子-电子散射（将电子动能转化为热量），(2)氢和氦的碰撞电离（产生二次电子，它们自己在介质中散射）和(3)碰撞激发（产生二次光子，我们也大致跟踪其命运）。对于最后一个过程，我们明确地包括所有向上层n≤4的过渡，以及向更高层次的良好动机外推。在所有情况下，我们使用最近计算的E < 1 keV的横截面和Bethe近似来推断更高的能量。我们计算了在适合于星系间介质的广泛条件下以热、电离（分别跟踪H i和氦种）和激发（分别跟踪H i Lyα）形式沉积的能量的分数。能量沉积分数取决于背景电离分数和电子能量，但几乎与背景密度无关。我们发现与一些，但不是全部，先前的高能计算很一致。我们的结果的电子表格是可用的。
We examine the fate of fast electrons (with energies E > 10 eV) in a thermal gas of primordial composition. To follow their interactions with the background gas, we construct a Monte Carlo model that includes: (1) electron–electron scattering (which transforms the electron kinetic energy into heat), (2) collisional ionization of hydrogen and helium (which produces secondary electrons that themselves scatter through the medium) and (3) collisional excitation (which produces secondary photons, whose fates we also follow approximately). For the last process, we explicitly include all transitions to upper levels n≤ 4, together with a well-motivated extrapolation to higher levels. In all cases, we use recent calculated cross-sections at E < 1 keV and the Bethe approximation to extrapolate to higher energies. We compute the fractions of energy deposited as heat, ionization (tracking H i and the helium species separately) and excitation (tracking H i Lyα separately) under a broad range of conditions appropriate to the intergalactic medium. The energy deposition fractions depend on both the background ionized fraction and the electron energy but are nearly independent of the background density. We find good agreement with some, but not all, previous calculations at high energies. Electronic tables of our results are available.