HERA: Unveiling the Cosmic Dawn

人类对理解宇宙和我们在宇宙中的位置的追求导致了我们这个时代的一些标志性的科学和技术成就。 这些包括宇宙微波背景的发现，宇宙加速膨胀的发现，以及使用各种观测技术来描述宇宙学的特征。 科学家们已经测量了六个关键的宇宙学参数，这些参数非常精确地控制着宇宙的几何形状，但是他们还没有把这些点联系起来，以了解大爆炸早期结构的种子是如何演变成今天在本地宇宙中看到的恒星、星系和黑洞的。 特别是，很少有被称为“宇宙黎明”的时期的观测，当时宇宙大约有100到10亿年的历史。 在宇宙黎明期间，第一批恒星和星系由大爆炸期间合成的原始氢气形成。 当恒星在超新星中发光、燃烧和爆炸时，它们释放的能量开始加热并吸收尚未被困在星系中的氢。 今天，天文学家观察到星系之间几乎所有的氢都被重新电离成等离子体状态。 发生这种情况的时间被称为再电离时代。 该项目将使用氢再电离时代阵列（HERA），一个专门建造的望远镜，测量和表征宇宙从宇宙黎明到再电离时代的宇宙，以填补这一关键空白。 天文学在整个社会中具有广泛的兴趣，并为年轻人提供了一个很好的科学和技术介绍。 为了给服务不足的学生带来这种影响，HERA制定了一个名为CHAMP的本科生外展计划，该计划是HERA合作机构中代表性不足的少数民族的重要暑期实习计划。HERA是一个与美国，英国，加拿大，意大利和南非合作的国际项目。 该望远镜正在南非北开普省卡鲁地区的南非射电天体物理观测站卡鲁天文保护区进行建设。 从2019年开始，HERA将包括350个彼此靠近的14米天线，工作频率为50-250 MHz。 卡鲁地区已被确定为一个特殊的“无线电静默”区，这意味着我们正在努力将人类通过我们的技术产生的无线电频率辐射的影响降到最低。 目前，HERA正在测量由于氢气的红移超精细跃迁而产生的发射，其静止频率为1420 MHz。 宇宙的膨胀使这些频率红移到50-250 MHz，这是宇宙黎明和再电离时代所预期的宇宙年龄。 考虑到气体在这些红移上的预期结构，信号预计将在光谱上与更明亮的前景区分开来，前景主要是来自我们银河系同步辐射的光谱平滑发射。 鉴于其灵敏度和特殊用途的设计，HERA预计将准确地测量这一时期的再电离分数。 这项测量将使我们能够了解宇宙的宇宙学和天体物理学在其历史的这一过渡部分。这一奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

Humanity's quest to understand the Universe and our place in it has led to some of the hallmark scientific and technical achievements of our time. These include the discovery of the Cosmic Microwave Background, the discovery of the accelerating expansion of the Universe, and the use of a variety of observational techniques to characterize the cosmology of the Universe. Scientists have measured the six key cosmological parameters that govern the geometry of the Universe with great precision, but they have not yet connected the dots to understand how the seeds of early structure from the Big Bang evolved into the stars, galaxies, and black holes seen today in the local Universe. In particular, there are very few observations of a period known as the "Cosmic Dawn" when the Universe was approximately 100 to 1000 million years old. During the Cosmic Dawn, the first stars and galaxies formed out of a pristine hydrogen gas that was synthesized during the Big Bang. As stars lit up, burned, and exploded in supernovae, the energy they released started to heat and then ionize the hydrogen that was not yet trapped in galaxies. Today, astronomers observe that nearly all hydrogen between galaxies has been re-ionized into a plasma state. The time when this happened is called the Epoch of Reionization. This project will use the Hydrogen Epoch of Reionization Array (HERA), a purpose-built telescope, to measure and characterize the Universe from the Cosmic Dawn to the Epoch of Reionization, to fill in this critical gap. Astronomy has broad interest throughout society and serves as an excellent introduction to science and technology for young people. In order to bring this impact to under-served students HERA has instituted an undergraduate outreach program called CHAMP, which serves as a significant summer internship program for underrepresented minorities at HERA partner institutions.HERA is an international project with Partners in the US, UK, Canada, Italy and South Africa. The telescope is well under construction in the Karoo region of Northern Cape South Africa at the South African Radio Astrophysical Observatory's Karoo Astronomy Reserve. Starting in 2019, HERA will comprise 350 14-m antennas in close proximity to one another and operate from 50-250 MHz. The Karoo location has been established as a special "radio-quiet" zone, meaning that efforts are undertaken to minimize the impact of the radio frequency emission that humans generate through our technology. Currently operational, HERA is measuring the emission due to the red-shifted hyperfine transition of hydrogen gas, which has a rest frequency of 1420 MHz. The expansion of the Universe redshifts these frequencies down to 50-250 MHz at the age of the Universe expected for the Cosmic Dawn and Epoch of Reionization. Given the expected structure of the gas over these redshifts, the signal is expected to be spectroscopically distinguishable from the much brighter foreground, which is predominantly spectrally smooth emission from our Galaxy's synchrotron radiation. Given its sensitivity and special-purpose design, HERA is expected to accurately measure the reionization fraction over this span of epochs. This measurement will allow us to understand the cosmology and astrophysics of the Universe over this transitional portion of its history.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.