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arXiv 1003.3030astro-ph.GAastro-ph.SR
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麦哲伦星云中超新星遗迹的大小分布

On the size distribution of supernova remnants in the Magellanic Clouds

Carles Badenes, Dan Maoz, Bruce Draine

摘要:

超新星遗迹(SNRs)的物理尺寸在一些附近的星系遵循近似线性的累积分布,与预期的减速激波锋面。这归因于选择效应,或归因于大多数SNR以恒定速度在“自由膨胀”中传播到稀薄的环境介质中。我们编制了一份麦哲伦星云(MC)中77个已知SNRs的列表,并认为它们是过去20 kyr内发生爆炸的SNe的相当完整的记录,其中大多数现在处于绝热阶段,Sedov阶段。大致线性的累积尺寸分布(在差分分布中均匀)可以由以下因素的组合产生:在该阶段期间的减速、在取决于局部气体密度的半径处向辐射损失主导的阶段的过渡、以及大致随ρ ^{-1}变化的环境密度的分布。这一解释得到了三个独立密度示踪物的幂律分布的支持:HI柱密度、H α表面亮度和来自分辨的恒星星族的恒星形成率。在这张图中,观测到的信噪比大小分布在r~30 pc处的截止值是由于超新星(SNe)爆炸区域的平均环境气体密度最小。我们发现,M33的SNR大小分布相似的MC,这表明这些功能,他们的解释,可能是普遍的。在一篇配套论文(Maoz & Badenes 2010)中,我们使用我们的SNR样本作为有效的“SN调查”来计算MC中的SN率和延迟时间分布。假设大多数SNR是在自由膨胀,而不是在Sedov阶段的演变,将导致SN率是在强烈的冲突与独立的测量,并与基本的恒星演化理论。

英文摘要:

The physical sizes of supernova remnants (SNRs) in a number of nearby galaxies follow an approximately linear cumulative distribution, contrary to what is expected for decelerating shock fronts. This has been attributed to selection effects, or to a majority of SNRs propagating in "free expansion", at constant velocity, into a tenuous ambient medium. We compile a list of 77 known SNRs in the Magellanic Clouds (MCs), and argue that they are a fairly complete record of the SNe that have exploded over the last ~20kyr, with most now in the adiabatic, Sedov phase of their expansions. The roughly linear cumulative size distribution (uniform in a differential distribution) can result from the combination of a deceleration during this phase, a transition to a radiation-loss-dominated phase at a radius that depends on the local gas density, and a distribution of ambient densities varying roughly as rho^{-1}. This explanation is supported by the observed -1 power-law distributions of three independent tracers of density: HI column density, Halpha surface brightness, and star formation rate from resolved stellar populations. In this picture, the observed cutoff at r~30 pc in the SNR size distribution is due to a minimum in the mean ambient gas density in the regions where supernovae (SNe) explode. We show that M33 has a SNR size distribution similar to that of the MCs, suggesting these features, and their explanation, may be universal. In a companion paper (Maoz & Badenes 2010), we use our sample of SNRs as an effective "SN survey" to calculate the SN rate and delay time distribution in the MCs. The hypothesis that most SNRs are in free expansion, rather than in the Sedov phase of their evolution, would result in SN rates that are in strong conflict with independent measurements, and with basic stellar evolution theory.

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