Forced accretion in stochastically fed AGN and quasars
Forced accretion in stochastically fed AGN and quasars
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随机供给活动星系核和类星体中的强迫吸积
DOI：
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发表时间：
2007
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通讯作者：
A. King
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作者：
S. Nayakshin;A. King
已知大于~ 0.01-0.1 pc的稳态吸积盘对于解释超大质量黑洞（SMBH）活动所需的吸积速率来说是引力不稳定的。我们提出SMBH是由一系列具有随机定向角动量的质量沉积事件馈送的。由于角动量的不完全抵消，一个扭曲的吸积盘在几秒差距内形成。磁盘的方向执行随机游动。新物质的沉积促进SMBH的吸积速度比粘性物质快得多。这张照片的观测意义包括：(i)较轻的吸积盘可以为AGN和类星体提供燃料，但避免了R >> 0.1 pc的恒星形成；（ii）盘内恒星的形成不仅仅是质量吸积率的函数。它可以在高或低的吸积速率下发生，例如，当到达内部区域的云太少时。我们银河系的中心秒差距就是一个例子。（iii）圆盘可以按照AGN统一模型的要求形成~秒差距大小的康普顿厚度的模糊结构；（iv）早期宇宙中由于盘和黑洞旋转错位导致的黑洞生长速度加快；(v)星系凸起中SMBH能量和动量反馈的各向同性沉积。这可能有助于解释它在宇宙中运作的高效率。超大质量黑洞的活动与银河系凸起中存在千秒差距尺度条或气体盘之间没有相关性；合并星系的气体组分之间的物理碰撞促进了气体流的产生，这些气体流供给合并星系的中心。因此，合并应该成为中小企业企业增长的催化剂。相反，经历较少合并的星系更有可能形成大质量的核星团，而不是为它们的SMBHs提供能量。
Steady state accretion discs larger than ~ 0.01-0.1 pc are known to be gravitationally unstable for the accretion rates needed to explain super-massive black hole (SMBH) activity. We propose that SMBH are fed by a succession of mass deposition events with randomly directed angular momenta. Because of incomplete angular momentum cancellation a warped accretion disc forms in the inner few parsec. The orientation of the disc performs a random walk. Deposition of new material promotes SMBH accretion at rates much faster than viscous. Observational implications of this picture include: (i) lighter accretion discs that can fuel AGN and quasars and yet avoid star formation at R >> 0.1 pc; (ii) star formation inside the disc is not a function of mass accretion rate only. It can take place at high or low accretion rates, e.g., when too few clouds arrive in the inner region. An example of this might be the central parsec of our Galaxy. (iii) The discs can form Compton-thick obscuring structures of ~ parsec size as required in AGN unification models; (iv) faster black hole growth resulting from misalignment of the disc and the black hole spin in the early Universe; (v) Isotropic deposition of SMBH energy and momentum feedback in the galaxy bulge. This may help explain the high efficiency with which it seems to be operating in the Universe. (vi) No correlation between SMBH activity and the presence of kiloparsec scale bars or gaseous discs in galactic bulges; (vii) Bodily collisions between gaseous components of merging galaxies facilitate production of gas streams feeding the centre of the combined galaxy. Mergers should thus be catalysts of SMBH growth. (viii) Conversely, galaxies experiencing fewer mergers are more likely to form massive nuclear star clusters than feed their SMBHs.