Title: A Population of Bona Fide Intermediate Mass Black Holes Identified as Low Luminosity Active Galactic Nuclei Show Chinese title

Title: 一个真实中等质量黑洞种群被识别为低光度活动星系核

Abstract: Nearly every massive galaxy harbors a supermassive black hole (SMBH) in its nucleus. SMBH masses are millions to billions $M_{\odot}$, and they correlate with properties of spheroids of their host galaxies. While the SMBH growth channels, mergers and gas accretion, are well established, their origin remains uncertain: they could have either emerged from massive "seeds" ($10^5-10^6 M_{\odot}$) formed by direct collapse of gas clouds in the early Universe or from smaller ($100 M_{\odot}$) black holes, end-products of first stars. The latter channel would leave behind numerous intermediate mass black holes (IMBHs, $10^2-10^5 M_{\odot}$). Although many IMBH candidates have been identified, none is accepted as definitive, thus their very existence is still debated. Using data mining in wide-field sky surveys and applying dedicated analysis to archival and follow-up optical spectra, we identified a sample of 305 IMBH candidates having masses $3\times10^4<M_{\mathrm{BH}}<2\times10^5 M_{\odot}$, which reside in galaxy centers and are accreting gas that creates characteristic signatures of a type-I active galactic nucleus (AGN). We confirmed the AGN nature of ten sources (including five previously known objects which validate our method) by detecting the X-ray emission from their accretion discs, thus defining the first bona fide sample of IMBHs in galactic nuclei. All IMBH host galaxies possess small bulges and sit on the low-mass extension of the $M_{\mathrm{BH}}-M_{\mathrm{bulge}}$ scaling relation suggesting that they must have experienced very few if any major mergers over their lifetime. The very existence of nuclear IMBHs supports the stellar mass seed scenario of the massive black hole formation. Show Chinese abstract

Abstract: 几乎每个大质量星系的核部都拥有一个超大质量黑洞（SMBH）。SMBH的质量是数百万到数十亿$M_{\odot}$，并且它们与宿主星系的球状结构特性相关。虽然SMBH的增长渠道，即合并和气体吸积，已被广泛确立，但它们的起源仍然不确定：它们可能源自早期宇宙中由气体云直接坍缩形成的巨大“种子”（$10^5-10^6 M_{\odot}$），也可能源自较小的（$100 M_{\odot}$）黑洞，这些是第一代恒星的最终产物。后一种渠道会留下大量中等质量黑洞（IMBHs，$10^2-10^5 M_{\odot}$）。尽管已经发现了许多IMBH候选体，但没有一个是被确认的，因此它们的存在仍然存在争议。通过在大视场天空调查中进行数据挖掘，并对存档和后续光学光谱进行专门分析，我们识别出一个包含305个IMBH候选体的样本，其质量为$3\times10^4<M_{\mathrm{BH}}<2\times10^5 M_{\odot}$，这些候选体位于星系中心，并正在吸积气体，从而产生类型I活动星系核（AGN）的特征特征。通过检测其吸积盘的X射线辐射，我们证实了十个源的AGN性质，其中包括五个之前已知的物体，这验证了我们的方法，从而定义了银河核中第一个真正的IMBH样本。所有IMBH宿主星系都具有小的隆起，并位于$M_{\mathrm{BH}}-M_{\mathrm{bulge}}$的尺度关系的低质量延伸上，这表明它们在其生命周期中很可能经历了很少甚至没有主要的合并。核IMBH的存在支持了大质量黑洞形成中的恒星级种子情景。