z~4.8处的黑洞质量和增长率：一个伴随短占空比活动的快速增长的短插曲
Black-Hole Mass and Growth Rate at z~4.8: A Short Episode of Fast Growth Followed by Short Duty Cycle Activity
摘要：
本文对Sloan数字巡天中的40个z~4.8活动星系核进行了新的Gemini-North/NIRI和VLT/SINFONI H波段光谱分析。这个样本可能包含了在这个红移下质量最大的活动黑洞（BH），并且辐射热光度范围很广，2.7x10^46< L_bol < 2.4x10^47 erg/sec。高质量的观测和对MgII（2800 A）谱线的精确拟合，使我们能够系统地研究BH质量（M_BH）和z~4.8的归一化吸积率（L/L_Edd）的分布。我们发现10^8 < M_BH < 6.6x10^9 M_sun，中值约为8.4x10^8 M_sun。我们还发现，0.2 < L/L_Edd < 3.9，中值约为0.6。这些源中的大多数都有足够的时间从z=20增长到z~4.8的观测质量，假设种子BH质量的范围，其中约40%的小到足以成为恒星残余。与先前在z~2.4和3.3处研究的样品相比，z~4.8 BH的质量通常低~0.5 dex。并且它们的L/L_Edd高出相似的因子。新的z~4.8样本可以被认为是z~2.4和3.3处最大质量BH的祖先种群。这样的演化解释要求BH从z~4.8到z~3.3和z~2.4的增长以短占空比进行，约10- 20%，这取决于特定的增长场景。
英文摘要：
We present new Gemini-North/NIRI and VLT/SINFONI H-band spectroscopy for a flux limited sample of 40 z~4.8 active galactic nuclei, selected from the Sloan Digital Sky Survey. The sample probably contains the most massive active black holes (BHs) at this redshift and spans a broad range in bolometric luminosity, 2.7x10^46< L_bol < 2.4x10^47 erg/sec. The high-quality observations and the accurate fitting of the MgII(2800A) line, enable us to study, systematically, the distribution of BH mass (M_BH) and normalized accretion rate (L/L_Edd) at z~4.8. We find that 10^8 < M_BH < 6.6x10^9 M_sun, with a median of ~8.4x10^8 M_sun. We also find that 0.2 < L/L_Edd < 3.9 with a median of ~0.6. Most of these sources had enough time to grow to their observed mass at z~4.8 from z=20, assuming a range of seed BH masses, with ~40% that are small enough to be stellar remnants. Compared to previously studied samples at z~2.4 and 3.3, the masses of the z~4.8 BHs are typically lower by ~0.5 dex. and their L/L_Edd is higher by a similar factor. The new z~4.8 sample can be considered as the progenitor population of the most massive BHs at z~2.4 and 3.3. Such an evolutionary interpretation requires that the growth of the BHs from z~4.8 to z~3.3 and z~2.4 proceeds with short duty cycles, of about 10-20%, depending on the particular growth scenario.
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