The Extreme Galaxy Reference Sample: Low Metallicity Galaxies Across Cosmic Time

微弱、低质量的星系在宇宙学上具有重要意义：数量众多，红移较大，它们最有可能是重新电离宇宙的光子的来源。对这类星系的描述仍然是天体物理学的关键问题之一。该项目将创建一个可公开获得的高度电离星系的参考样本，即极端星系参考样本(EGRS)。EGRS将被用来量化低金属丰度星系及其周围气体、局部宇宙和恒星形成高峰期性质的多样性。关于星系中可能重新电离宇宙的物理条件，最广泛的知识并不是直接研究再电离时代的源，而是对低红移和中等红移的看似相似的天体进行了详细的研究。该项目包括一个多层次的战略，与许多受众分享科学，从普通公众到本科生，包括课程开发、推广和对未被充分代表的人群的学生的指导。突出的问题包括使电离辐射逃逸的因素，最极端和高度电离的星系的内在电离光谱，以及反馈在塑造环星系介质(CGM)属性和使电离光子逃逸方面的作用。EGRS有两部分：1)局部宇宙极端普查(EXCLU)，这是一项使用四个波长相邻的窄带滤光片覆盖26,470平方度的极宽区域的成像调查，将发现局部宇宙中数万个最稀有和最极端的星系，并能够研究它们的晕质量、演化状态、恒星群、本征电离光谱和反馈相关性质；以及2)对红移约2的较小的、精心选择的星系样本进行综合研究，以Lyman-α发射绘制CGM图，并用深度静止帧紫外线成像量化反馈，辅之以更高的信噪比、更高的信号噪声比和更高的紫外成像。引力透镜星系的更高分辨率研究。EGRS将为社区提供跨宇宙时间研究低质量、低金属丰度星系的基线。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Faint, low-mass galaxies are a population of cosmological importance: numerous at high redshifts, they are the most likely source of the photons that re-ionized the universe. Characterization of such galaxies remains one of the key problems in astrophysics. This project will create a publicly-available reference sample of the most highly ionized galaxies, the Extreme Galaxy Reference Sample (EGRS). The EGRS will be used to quantify the diversity in the properties of low-metallicity galaxies and their surrounding gas, in the local universe and at the peak epoch of star formation. The most extensive knowledge of the physical conditions in the galaxies that likely re-ionized the universe comes not from studying reionization-era sources directly, but from detailed examination of plausibly similar objects at low and moderate redshifts. The project includes a multi-layered strategy of sharing science with many audiences, from the general public to undergraduate students, and including curriculum development, outreach, and mentoring of students from under-represented populations.Outstanding questions include the factors that enable the escape of ionizing radiation, the intrinsic ionizing spectra of the most extreme and highly ionized galaxies, and the role of feedback in shaping the properties of the circumgalactic medium (CGM) and enabling ionizing photon escape. The EGRS has two pieces: 1) the Extreme Census of the Local Universe (ExCLU), an imaging survey using four wavelength-adjacent narrowband filters to cover an extraordinarily wide area of 26,470 square degrees that will find tens of thousands of the rarest and most extreme galaxies in the local universe, and enabling studies of their halo masses, evolutionary states, stellar populations, intrinsic ionizing spectra and feedback-related properties, and 2) comprehensive studies of a smaller, carefully selected sample of galaxies at redshift about two, to map the CGM with Lyman-alpha emission and quantify feedback with deep rest-frame ultraviolet imaging, supplemented by higher signal-to-noise, higher resolution studies of gravitationally lensed galaxies. EGRS will provide the community with a baseline for the study of low-mass, low-metallicity galaxies across cosmic time.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.