Dissecting galaxies with bright stars and HII regions

这个项目解决了两个长期存在的关于星系距离和化学丰度的问题：首先，需要一个距离指示器，它对星际尘埃和星系内化学丰度的变化都不敏感；其次，需要一种更好的方法来从恒星形成区域的光谱中推断星系的化学成分。PI和co-PI将发展通量加权重力-光度关系（FGLR）技术，通过该技术，光谱B类和A类超巨星可以作为距离测量的“标准蜡烛”。该技术利用光谱学来获得这些恒星的单个表面重力、金属丰度、温度以及光度。他们将通过对麦哲伦星云、M31和IC1316的观测来校准这种方法。通过对目标星系额外样本中的超巨星和HII区域的后续光谱分析，他们将通过精确的恒星和星云丰度来约束恒星形成星系的演化状态，研究螺旋星系的径向丰度梯度，并表征金属丰度对河外距离尺度中使用的其他重要技术的影响。光谱工作建立在一个详细的恒星大气模型库上，他们将对其进行改进，并将其公之于众。这项工作将为未来几代大型望远镜提供合适的策略。博士后研究员将在此资助下得到支持和指导。

This project addresses two long-standing issues concerning the distances and chemical abundances of galaxies: first, the need for a distance indicator that is insensitive to both patchy interstellar dust and to variations in chemical abundances within a galaxy; and second, the need for a better method to infer the chemical compositions of galaxies from the spectra of star forming regions. The PI and co-PI will develop the flux-weighted gravity-luminosity relation (FGLR) technique, through which spectral class B and A supergiant stars can be used as "standard candles" in distance measurements. The techniques employs optical spectroscopy to obtain individual surface gravities, metallicities, temperatures, and thereby luminosities of these stars. They will calibrate this method with observations of the Magellanic Clouds, M31, and IC1316 . With subsequent spectroscopy of supergiant stars and HII regions in an additional sample of target galaxies, they will constrain the evolutionary states of star-forming galaxies from accurate stellar and nebular abundances, study radial abundance gradients in spiral galaxies, and characterize the effect of metallicity on other important techniques used in the extragalactic distance scale. The spectroscopic work rests on a library of detailed model stellar atmospheres, which they will improve and make publicly available. The work will inform strategies appropriate for upcoming generations of large telescopes. A postdoctoral researcher will be supported and mentored under this grant.