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arXiv 1303.2664astro-ph.GAastro-ph.CO
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盘星系的超级气泡爆发和星系风

Superbubble breakout and galactic winds from disk galaxies

Arpita Roy, Biman B. Nath, Prateek Sharma, Yuri Shchekinov

摘要:

我们研究了盘状星系产生超级气泡的条件,这些超级气泡可以从盘状星系中爆发出来并产生星系风。我们认为,阈值表面密度的超新星速率播种风取决于超气泡能量的能力,以补偿辐射冷却。我们首先适应Kompaneets形式主义膨胀气泡在分层介质中的连续能量注入的情况下,包括辐射冷却的影响,在壳。借助流体动力学模拟,我们研究了具有典型圆盘参数的分层圆盘中超气泡的演化。我们确定了两个关键的能量注入率,其影响不同,相应的突破范围从温和到有力的。(a)以2-3量级的马赫数从盘中爆发出来的超气泡对应于10^{-4} erg cm^{-2} s^{-1}量级的能量注入率,这与在平面外区域具有同步加速器发射气体的盘星系有关。(b)一个更大的能量注入阈值,数量级为10^{-3} erg cm^{-2} s^{-1},或者等价地,恒星形成表面密度为\sim 0.1太阳质量yr^{-1} kpc^{-2},对应于马赫数为\sim 5-10的超级气泡。虽然温和的超级气泡可以由大的OB协会产生,但后一种需要超级星团。这些推导出的条件比较以及与观测的盘星系风和多相晕气体的存在。此外,我们发现,一般认为,通过瑞利-泰勒(RT)的不稳定性,当他们达到一个垂直高度的规模高度的顺序,超级气泡的碎片相反,首先受到典型的磁盘参数的热不稳定性和RT不稳定接管时,外壳达到的距离约两倍的规模高度。

英文摘要:

We study the conditions for disk galaxies to produce superbubbles that can break out of the disk and produce a galactic wind. We argue that the threshold surface density of supernovae rate for seeding a wind depends on the ability of superbubble energetics to compensate for radiative cooling. We first adapt Kompaneets formalism for expanding bubbles in a stratified medium to the case of continuous energy injection and include the effects of radiative cooling in the shell. With the help of hydrodynamic simulations, we then study the evolution of superbubbles evolving in stratified disks with typical disk parameters. We identify two crucial energy injection rates that differ in their effects, the corresponding breakout ranging from being gentle to a vigorous one. (a) Superbubbles that break out of the disk with a Mach number of order 2-3 correspond to an energy injection rate of order 10^{-4} erg cm^{-2} s^{-1}, which is relevant for disk galaxies with synchrotron emitting gas in the extra-planar regions. (b) A larger energy injection threshold, of order 10^{-3} erg cm^{-2} s^{-1}, or equivalently, a star formation surface density of \sim 0.1 solar mass yr^{-1} kpc^{-2}, corresponds to superbubbles with a Mach number \sim 5-10. While the milder superbubbles can be produced by large OB associations, the latter kind requires super-starclusters. These derived conditions compare well with observations of disk galaxies with winds and the existence of multiphase halo gas. Furthermore, we find that contrary to the general belief that superbubbles fragment through Rayleigh-Taylor (RT) instability when they reach a vertical height of order the scale height, the superbubbles are first affected by thermal instability for typical disk parameters and that RT instability takes over when the shells reach a distance of approximately twice the scale height.

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