AMUSE-处女座II。黑洞吸积中的尺度缩减
AMUSE-Virgo II. Down-sizing in black hole accretion
摘要：
我们完成了对100个早期室女座星系的核X射线活动的普查，这些星系是由钱德拉X射线望远镜观测的，作为AMUSE室女座巡天的一部分，在0.5-7 keV范围内，它们的（3sigma）极限光度为3.7E+38 erg/s。目标样本的恒星质量分布，这主要是由正式的“不活跃”的星系，峰值低于1 E +10 M_太阳，一个政权的核超大质量黑洞（SMBHs）的存在是有争议的。在100个物体中，有32个显示了核X射线源，包括6个混合核，它们也拥有一个巨大的核簇，从档案HST图像中可以看到。在仔细考虑了基于X射线光度函数的形状和归一化的核低质量X射线双星的污染后，我们得出结论，在我们的样本中，24-34%的星系拥有X射线活跃的SMBH（在95%C. L）。这就为星系团环境中附近凸起的黑洞占据率设定了一个严格的下限。从表面上看，活动部分-下降到我们的光度极限-被发现与主机恒星质量增加。然而，考虑到选择效应，我们发现平均Eddington标度X射线光度与黑洞质量的标度为M_BH^（-0.62 ^{+0.13}-0.12}），内禀散射为0.46^（{+0.08}-0.06}）dex.这一发现可以解释为观测证据“缩小”的黑洞吸积在当地的早期类型，也就是说，低质量的黑洞发光相对更接近其爱丁顿极限比更高质量的对象。因此，活跃星系（定义为高于固定X射线爱丁顿比的星系）的比例随着黑洞质量的增加而减少。
英文摘要：
(Abridged) We complete the census of nuclear X-ray activity in 100 early type Virgo galaxies observed by the Chandra X-ray Telescope as part of the AMUSE-Virgo survey, down to a (3sigma) limiting luminosity of 3.7E+38 erg/s over 0.5-7 keV. The stellar mass distribution of the targeted sample, which is mostly composed of formally `inactive' galaxies, peaks below 1E+10 M_Sun, a regime where the very existence of nuclear super-massive black holes (SMBHs) is debated. Out of 100 objects, 32 show a nuclear X-ray source, including 6 hybrid nuclei which also host a massive nuclear cluster as visible from archival HST images. After carefully accounting for contamination from nuclear low-mass X-ray binaries based on the shape and normalization of their X-ray luminosity function, we conclude that between 24-34% of the galaxies in our sample host a X-ray active SMBH (at the 95% C.L.). This sets a firm lower limit to the black hole occupation fraction in nearby bulges within a cluster environment. At face value, the active fraction -down to our luminosity limit- is found to increase with host stellar mass. However, taking into account selection effects, we find that the average Eddington-scaled X-ray luminosity scales with black hole mass as M_BH^(-0.62^{+0.13}_{-0.12}), with an intrinsic scatter of 0.46^({+0.08}_{-0.06}) dex. This finding can be interpreted as observational evidence for `down-sizing' of black hole accretion in local early types, that is, low mass black holes shine relatively closer to their Eddington limit than higher mass objects. As a consequence, the fraction of active galaxies, defined as those above a fixed X-ray Eddington ratio, decreases with increasing black hole mass.
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