高质量黑洞致密星系的起源
The origin of compact galaxies with anomalously high black hole masses
摘要：
对局部星系中存在质量相对于恒星质量非常高的超大质量黑洞（BH）的观测结果似乎与星系与其中心黑洞共同演化的简单模型不一致。我们研究的起源，这样的离群值在一个Lambda冷暗物质的背景下使用EAGLE宇宙学，流体动力学模拟。我们发现了15个“M_BH（M_star）-outlier”星系，它们被定义为M_BH比模拟中的M_BH（M_star）关系高出1.5 dex。所有M_BH（M_star）-异常星系都是卫星星系，典型的M_star ~ 10^10 M_sun和M_BH ~ 10^8 M_sun。它们都成为异常值，因为它们的外层恒星成分的潮汐剥离作用超过了几个Gyr和早期形成时间，导致高红移时BH的快速增长，前一种机制对67%的异常值最为重要。同样的机制也导致M_BH（M_star）-离群卫星星系在模拟中是最紧凑的星系之一，使它们成为超紧凑矮星系祖先的理想候选者。在z=0处发现的10个最极端的中心星系（log_{10}（M_BH/ M_{BH,med}）在[1.2，1.5]中）在M_BH中迅速增长，在早期（z > 2）远远高于现在的M_BH-M_star关系，并且要么继续平行于z=0关系演化，要么直到今天保持不变，使它们成为高红移宇宙的“遗迹”。这种高z的形成机制可能有助于解释观测到的M_BH（M_star）异常值的起源，这些异常值具有扩展的暗物质晕和未受干扰的形态。
英文摘要：
Observations of local galaxies harbouring supermassive black holes (BHs) of anomalously high mass, M_BH, relative to their stellar mass, M_star, appear to be at odds with simple models of the co-evolution between galaxies and their central BHs. We study the origin of such outliers in a Lambda cold dark matter context using the EAGLE cosmological, hydrodynamical simulation. We find 15 'M_BH(M_star)-outlier' galaxies, defined as having M_BH more than 1.5 dex above the median M_BH(M_star) relation in the simulation, M_{BH,med}. All M_BH(M_star)-outliers are satellite galaxies, typically with M_star ~ 10^10 M_sun and M_BH ~ 10^8 M_sun. They have all become outliers due to a combination of tidal stripping of their outer stellar component acting over several Gyr and early formation times leading to rapid BH growth at high redshift, with the former mechanism being most important for 67 per cent of these outliers. The same mechanisms also cause the M_BH(M_star)-outlier satellites to be amongst the most compact galaxies in the simulation, making them ideal candidates for ultracompact dwarf galaxy progenitors. The 10 most extreme central galaxies found at z=0 (with log_{10}(M_BH/M_{BH,med}) in [1.2, 1.5]) grow rapidly in M_BH to lie well above the present-day M_BH-M_star relation at early times (z > 2), and either continue to evolve parallel to the z=0 relation or remain unchanged until the present day, making them 'relics' of the high-redshift universe. This high-z formation mechanism may help to explain the origin of observed M_BH(M_star)-outliers with extended dark matter haloes and undisturbed morphologies.
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