长期演化和最后7 Gyr中不演化的黑洞与星系质量比
Secular evolution and a non-evolving black hole to galaxy mass ratio in the last 7 Gyr
摘要：
本文对XMM-COSMOS巡天的32个1型活动星系核（AGNs）样本（M_BH/M_sun~10^（7.2--8.7））的黑洞（BH）质量与星系恒星总质量之比在0.3<z<0.9处提出了新的限制。基于H_β的维里M_BH估计可从COSMOS Magellan/IMACS巡天获得。我们利用高分辨率的哈勃空间望远镜（HST）图像对各第1类活动星系核和宿主星系的光进行分解，并采用特制的质光比来估算恒星质量（M *）。对于星系核球的质量，M_BH/M_* 比相对于局域关系为零，并且我们也发现质量比M_BH/M_*=（1+z）^{0.02+-0.34}在z~0.9范围内没有演化。有趣的是，在高M_BH端，z=0的关系有一个正的偏移，这可以完全由宇宙散射为0.3的质量函数偏差来解释，重申了内在分布与零演化是一致的。从我们的结果中，我们得出结论，由于z~0.9，不需要大量增加恒星质量：恒星形成率的下降和z<1时的合并活动支持这种情况。然而，考虑到这些星系中有相当一部分显示出盘状成分，它们的凸起确实质量不足。这直接表明，对于最后7 Gyr，这些星系遵守z=0关系所需的唯一基本机制是恒星质量重新分配到凸起，可能是由长期过程驱动的，即，内部不稳定和轻微合并。
英文摘要：
We present new constraints on the ratio of black hole (BH) mass to total galaxy stellar mass at 0.3<z<0.9 for a sample of 32 type-1 active galactic nuclei (AGNs) from the XMM-COSMOS survey covering the range M_BH/M_sun~10^(7.2--8.7). Virial M_BH estimates based on H_beta are available from the COSMOS Magellan/IMACS survey. We use high-resolution Hubble Space Telescope (HST) imaging to decompose the light of each type-1 AGN and host galaxy, and employ a specially-built mass-to-light ratio to estimate the stellar masses (M_*). The M_BH-M_* ratio shows a zero offset with respect to the local relation for galactic bulge masses, and we also find no evolution in the mass ratio M_BH/M_*=(1+z)^{0.02+-0.34} up to z~0.9. Interestingly, at the high-M_BH end there is a positive offset from the z=0 relation, which can be fully explained by a mass function bias with a cosmic scatter of 0.3, reaffirming that the intrinsic distribution is consistent with zero evolution. From our results we conclude that since z~0.9 no substantial addition of stellar mass is required: the decline in star formation rates and merger activity at z<1 support this scenario. Nevertheless, given that a significant fraction of these galaxies show a disk component, their bulges are indeed undermassive. This is a direct indication that for the last 7 Gyr the only essential mechanism required in order that these galaxies obey the z=0 relation is a redistribution of stellar mass to the bulge, likely driven by secular processes, i.e., internal instabilities and minor merging.
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