Raising the bar for black hole mass measurements in lower mass galaxies

现在我们知道，超大质量黑洞存在于所有星系的中心。在过去的十年里，科学家们发现，这些巨型黑洞的质量在很大程度上取决于它们所在星系的性质。超大质量黑洞是宇宙中最有趣的物体之一，它在母星系的演化过程中也发挥着革命性的作用。虽然超大质量黑洞非常巨大（质量是太阳的100万到100亿倍），但它们只占它们所在星系总质量的千分之一。关于这些黑洞是如何形成的，以及它们是如何如此戏剧性地影响星系演化的，我们仍然知之甚少。要了解黑洞是如何成长的，首先有必要测量它们的质量，无论是在附近的星系还是在遥远的星系。测量邻近星系黑洞质量的“黄金标准”方法是利用靠近黑洞轨道的恒星的运动。在邻近的宇宙中，大多数仍在生长的黑洞（所谓的活动星系核）生活在像我们银河系这样的盘状星系中。盘状星系中的黑洞质量较小，因此更难研究，因为它们对周围恒星运动的影响较小。该团队将开发培训工具，以便其他科学家使用他们的新建模软件。几名本科生将参与这项研究，以增加他们的科学和技术训练，并为他们未来的追求提供更好的装备。在低红移和高红移的情况下，对星系中超大质量黑洞质量的精确测定，几乎是理解星系演化的所有努力的基础。利用星系核中恒星的动力学来测量黑洞质量是目前的“黄金标准”。人们发现，黑洞的质量在很大范围内（从太阳质量的1亿倍到100亿倍）与其宿主星系的性质密切相关。在主要存在于盘状星系的较低质量黑洞中，这种相关性较弱。像我们的银河系这样的螺旋星系，包含一个恒星条（一个快速旋转的雪茄状中心特征），显示出最分散。研究小组最近发现，在棒状星系中，当棒状星系被忽略时，黑洞质量的测量值可能会被高估，尤其是当星系被更正面地观察时。由于65%的盘状星系都有恒星条，这种偏差主要影响质量函数低端星系的黑洞质量。它还影响黑洞质量尺度关系——宿主星系属性和黑洞质量之间的相关性。这个项目产生的新的黑洞质量测量将更好地限制黑洞质量范围低端的统计不确定性，这是最不确定的。它们还将有助于确定“混响映射”质量尺度，这一关系对未来测量高红移黑洞质量至关重要。该模型将生成宿主星系核中恒星轨道的详细三维分布。在这个项目期间将开发的开源软件将具有广泛的适用性，超出黑洞质量测定。该团队还将提供使用该软件进行星系建模的教程，并让几名本科生参与研究，使他们能够将最先进的星系动力学建模工具应用于实际数据。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

It is now known that supermassive black holes live at the centers of all galaxies. Over the past decade scientists have found that the masses of these monster black holes depend strongly on the properties of their host galaxies. Supermassive black holes, some of the most intriguing objects in the universe, also play a transformative role in how their parent galaxies evolve. While they are gigantic (between a million and a ten billion times the mass of the sun), supermassive black holes are only a fraction of a percent of the total mass of the galaxy they live in. Much is still not understood about how these black holes grew or how they were able to so dramatically influence galaxy evolution. To understand how black holes grow, it is first necessary to measure their masses, both in nearby galaxies and in distant galaxies. The ‘gold standard’ method for measuring black hole masses in nearby galaxies uses the motions of stars that orbit close to the black hole. In the nearby Universe most of the black holes that are still growing today (the so-called Active Galactic Nuclei) live in disk galaxies like our own Milky Way. The black holes in disk galaxies are less massive, and therefore are harder to study since they have weaker effects on the motion of stars around them. The team will develop training tools to allow other scientists to use their new modeling software. Several undergraduate research students will participate in this research adding to their scientific and technical training and better equipping them for future pursuits.The accurate determination of supermassive black hole masses in galaxies, both at low and high redshifts, underpins almost all efforts to understand galaxy evolution. Black hole mass measurements that use the dynamics of stars in galactic nuclei are the current ‘gold standard’. Black hole masses are found to be tightly correlated with the properties of their host galaxies over a very wide range of black hole masses (from 100 million to 10 billion times the mass of the sun). At lower black holes masses, found in predominantly disk-like galaxies, the correlations are weaker. Spiral galaxies like our Milky Way, that contain a stellar bar (a rapidly rotating cigar-like central feature) show the most scatter. The team recently found that black hole mass measurements in barred galaxies can be overestimated when the bar is ignored, especially as the galaxy is viewed more face-on. Since 65% of disk galaxies have stellar bars, this bias primarily affects black hole masses in galaxies at the low-end of the mass function. It also impacts the black hole mass scaling relations - the correlations between the host galaxy properties and black hole masses. The new black hole mass measurements resulting from this project will better constrain the statistical uncertainties on the black hole masses at the low end of the black hole mass range, where it is most uncertain. They will also aid in determining the “reverberation mapping” mass scale a relationship that is crucial for future measurements of black hole masses at high redshift. The modeling will yield detailed three-dimensional distributions of the orbits of stars in the host galactic nuclei. The open source software that will be developed during this project will have broad applicability beyond black hole mass determination. The team will also make available tutorials for using the software for modeling galaxies and involve several undergraduates in the research allowing them to apply state-of- the-art galactic dynamics modeling tools to real data.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.