Dissecting galaxies with bright stars and HII regions

该项目解决了有关星系距离和化学丰度的两个长期存在的问题：首先，需要一种对斑驳的星际尘埃和星系内化学丰度变化不敏感的距离指示器；其次，需要一种更好的方法从恒星形成区域的光谱推断星系的化学成分。 PI和co-PI将开发通量加权重力光度关系（FGLR）技术，通过该技术，光谱B级和A级超巨星可以用作距离测量中的“标准烛光”。该技术利用光谱学来获取这些恒星的单独表面重力、金属丰度、温度，从而获取这些恒星的光度。他们将通过对麦哲伦星云、M31 和 IC1316 的观测来校准该方法。通过随后对额外目标星系样本中的超巨星和HII区域的光谱分析，他们将从精确的恒星和星云丰度中限制恒星形成星系的演化状态，研究螺旋星系中的径向丰度梯度，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。光谱工作依赖于详细的恒星大气模型库，他们将对其进行改进并公开。这项工作将为适合下一代大型望远镜的策略提供信息。一名博士后研究员将得到这笔资助的支持和指导。

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.