Unravelling obese black holes in the first galaxies
Unravelling obese black holes in the first galaxies
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解开第一个星系中的肥胖黑洞
DOI：
10.1093/mnras/stt696
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发表时间：
2013
影响因子：
4.8
通讯作者：
Agarwal B
中科院分区：
文献类型：
--
作者：
Agarwal B
我们预测在宇宙最初十亿年早期聚集的一类新天体的存在和观测特征：肥胖黑洞星系（OBG）。 OBG 是中心黑洞 (BH) 质量最初超过主星系恒星成分质量的天体，并且 BH 吸积产生的光度在星光中占主导地位。传统观点认为，第一批星系是随着第一批恒星的形成而发光的。我们在这里表明，事实上，可能存在一群天体物理物体，但情况并非如此。通过宇宙学模拟，我们证明了由于莱曼-沃纳辐射对氢分子的光解离效应，在某些位置恒星形成最初受到抑制，并且直接塌缩黑洞（DCBH）形成。我们证明 OBG 的形成是不可避免的，因为在早期宇宙中，在有利于 DCBH 形成的光环中找到所需的河外环境和正确的物理条件的概率相当高。我们估计 OBG 数密度为 0.009 Mpc−3atz∼ 8 和 0.03 Mpc−3atz∼ 6。从我们的模拟体积推断，我们推断检测到 atz≥ 6 的最亮类星体可能经历了早期的 OBG 阶段。追踪 DCBH 及其宿主星系在不断演化的暗物质晕中的生长历史表明，这些原始星系始于超大质量的 BH，并通过随后的合并和原位恒星形成获得恒星成分。在此过程中，它们不可避免地会经历一个 OBG 阶段，该阶段由不断增长的黑洞释放的爱丁顿速率或以下的吸积光度主导。 OBG 相的特征在于紫外 (UV) 光谱 fλ∝ λβ，斜率为 β ~ -2.3 并且不存在巴尔默断裂。 OBG 在空间上也应该是未解析的，并且预计比大多数已知的高红移星系更亮。它们还可以显示出广泛的高激发发射线，正如 I 型活动星系核所预期的那样，尽管 Nvand Civwill 等谱线的强度显然取决于宿主星系的化学富集。 OBG 可能会通过哈勃太空望远镜对 UltraVISTA 等广域地面巡天提供的较亮莱曼断裂星系样本进行后续成像来揭示，并且应该可以使用詹姆斯·韦伯太空望远镜上的仪器轻松发现和研究。 OBG 的发现和表征将为了解第一个黑洞的形成及其对早期星系形成的影响提供重要的见解。
We predict the existence and observational signatures of a new class of objects that assembled early, during the first billion years of cosmic time: obese black hole galaxies (OBGs). OBGs are objects in which the mass of the central black hole (BH) initially exceeds that of the stellar component of the host galaxy, and the luminosity from BH accretion dominates the starlight. Conventional wisdom dictates that the first galaxies light up with the formation of the first stars; we show here that, in fact, there could exist a population of astrophysical objects in which this is not the case. From a cosmological simulation, we demonstrate that there are sites where star formation is initially inhibited and direct-collapse black holes (DCBHs) form due to the photodissociating effect of Lyman–Werner radiation on molecular hydrogen. We show that the formation of OBGs is inevitable, because the probability of finding the required extragalactic environment and the right physical conditions in a halo conducive to DCBH formation is quite high in the early Universe. We estimate an OBG number density of 0.009 Mpc−3atz∼ 8 and 0.03 Mpc−3atz∼ 6. Extrapolating from our simulation volume, we infer that the most luminous quasars detected atz≥ 6 likely transited through an earlier OBG phase. Following the growth history of DCBHs and their host galaxies in an evolving dark matter halo shows that these primordial galaxies start off with an overmassive BH and acquire their stellar component from subsequent merging as well as in situ star formation. In doing so, they inevitably go through an OBG phase dominated by the accretion luminosity at the Eddington rate or below, released from the growing BH. The OBG phase is characterized by an ultraviolet (UV) spectrumfλ∝ λβwith a slope of β ∼ −2.3 and the absence of a Balmer break. OBGs should also be spatially unresolved, and are expected to be brighter than the majority of known high-redshift galaxies. They could also display broad high-excitation emission lines, as expected from type I active galactic nuclei, although the strength of lines such as Nvand Civwill obviously depend on the chemical enrichment of the host galaxy. OBGs could potentially be revealed viaHubble Space Telescopefollow-up imaging of samples of brighter Lyman-break galaxies provided by wide-area ground-based surveys such as UltraVISTA, and should be easily uncovered and studied with instruments aboard theJames Webb Space Telescope. The discovery and characterization of OBGs would provide important insights into the formation of the first BH, and their influence on early galaxy formation.
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发表时间：
2011-04
期刊：
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影响因子：
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