Probing the Gas that Fuels Star Formation in Typical High Redshift Galaxies

Regina Jorgenson博士被授予NSF天文学和天体物理学博士后奖学金，在夏威夷大学天文研究所(IFA)开展一项研究和教育计划。大型望远镜、灵敏仪器和深度探测的发展使天文学家能够在大爆炸(Z~8)后的数亿年后探测到高度恒星形成的星系。这些令人兴奋的发现隐含地集中在最极端类型的恒星爆发星系上，这些星系的光线可以在如此遥远的距离内被探测到。为了发展对星系形成的完整理解，这些研究必须以对典型星系的坚实理解为补充，即那些包含宇宙中大部分重子物质的星系。然而，研究这些典型的星系是困难的，因为它们通常太暗，无法在发射中直接检测到。相反，这些被称为阻尼莱曼阿尔法星系(DLA)的星系已经被探测到了对更遥远的背景类星体的吸收。虽然DLA已知包含宇宙中z=0-5之间的大部分中性气体，但它们在星系形成中的确切作用被它们的探测性质所掩盖--每个星系只有一条铅笔光束视线--因此，关于DLA的大小、质量、形态和运动学的了解并不多，留下了几个重要的问题：(1)由于大多数恒星形成燃料的高红移宿主，它们与恒星形成和恒星形成星系有什么联系？(2)它们在星系形成和演化场景中扮演什么角色？(3)虽然吸收线运动学与Z~2处的大质量螺旋星系是一致的，但这个模型对星系形成的分级理论提出了挑战，该理论预测在Z~2的大多数天体的圆速度远低于典型的大质量螺旋星系。为了理解DLA及其与恒星形成星系的联系，本提议旨在(1)利用OSIRIS，Keck望远镜上具有激光导星自适应光学(LGSAO)的灵敏的新的积分场单位(IFU)，有效地减去背景类星体光并直接成像H-α(和[N II])，[O III])已知具有较高恒星形成率的DLA样本的发射；以及(2)利用斯巴鲁望远镜的超高分辨率光谱仪来解析和探测被认为是DLA星系内恒星形成的前驱地点的非常冷和密集的速度分量的物理性质。观测和模拟表明，大约50%的DLA，那些具有高金属含量和高吸收率的DLA与明亮、致密的恒星形成结有关，其发射可以通过LGSAO OSIRIS IFU观测来探测到。奥西里斯将能够追踪速度剖面，并寻找旋转、流入或流出的证据。将电离气体中氧丰度的可靠指标[N II]/H-α比以及恒星形成的其他诊断方法与吸收线数据的诊断结果进行比较，将有助于更好地理解整个吸收线系统中的金属丰度梯度、运动学和恒星形成，并为星系形成的模拟提供重要的约束。对超高分辨率光谱的分析将补充这项研究，详细了解冷密云中的金属丰度和分子分布，这些云可能受到引力的限制，代表着DLAS中恒星形成的前驱地点。乔根森还将为初中生/高中生设计一门以探究为基础的天文学课程，并通过IFA久负盛名的HI STAR计划教授这门课程。该项目招募夏威夷原住民、少数族裔和社会经济背景较低的学生参加为期一周的天文学课程。拟议的课程将强调莫纳基亚山对天文研究的重要性，以及维持通往莫纳基亚山的和谐通道并可能在这座圣山上进一步发展所需的重要外联活动。此外，作为NSF本科生研究体验计划的一部分，至少将有三名本科生接受指导，特别关注鼓励女性和代表不足的少数族裔参与天文学。

Dr. Regina Jorgenson is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at the University of Hawaii Institute for Astronomy (IfA). The development of large telescopes, sensitive instruments and deep surveys has allowed astronomers to detect highly star-forming galaxies back to a few hundred million years after the Big Bang (z~8). These exciting discoveries are implicitly focused on the most extreme types of star-bursting galaxies, whose light can be detected over such great distances. To develop a complete understanding of galaxy formation, these studies must be augmented by a solid understanding of typical galaxies, i.e. those galaxies that contain the majority of the baryonic matter in the universe. However, studying these typical galaxies is difficult because they are generally too faint to be directly detected in emission. Instead, these galaxies, known as the Damped Lyman alpha Systems (DLAs), have been probed in absorption against more distant background quasars.While the DLAs are known to contain the majority of the neutral gas in the universe between z = 0-5, their precise role in galaxy formation is obscured by the nature of their detection--with only a pencil beam line of sight through each galaxy--and as a result not much is known about DLA sizes, masses, morphologies, and kinematics, leaving open several important questions: (1) As the high redshift hosts of the majority of the fuel for star formation, what is their connection with star formation and the star forming galaxies? (2) What is their role in galaxy formation and evolution scenarios? and (3) While the absorption line kinematics are consistent with massive spiral galaxies at z~2, this model poses a challenge to hierarchical theories of galaxy formation, which predict most objects at z2 to have circular velocities much less than those of typical massive spirals.To understand DLAs and their connection to the star forming galaxies, this proposal aims to (1) take advantage of OSIRIS, the sensitive, new Integral Field Unit (IFU) with laser guide star adaptive optics (LGSAO) on the Keck telescope, to effectively subtract the background quasar light and directly image the H-alpha (and [N II], [O III]) emission of a sample of DLAs known to have relatively high star formation rates; and (2) utilize the ultra-high resolution spectrograph of the Subaru telescope to resolve and probe the physics of the very cold and dense velocity components that are proposed to be progenitor sites of star formation within DLA galaxies.Observations and simulations suggest that ~50% of DLAs, those with high metallicities and star formation rates as measured by their absorption profiles, are associated with bright, compact knots of star formation, whose emission can be detected with the help of LGSAO OSIRIS IFU observations. OSIRIS will be able to trace the velocity profiles and look for evidence of rotation, inflow, or outflow. Comparing [N II]/H-alpha ratio, a reliable indicator of the oxygen abundance in the ionized gas, as well as other diagnostics of star formation with those of the absorption line data will lead to a greater understanding of metallicity gradients, kinematics and star formation in the entire population of absorption line systems and provide vital constraints on simulations of galaxy formation. Analysis of ultra-high resolution spectra will complement this study with detailed understanding of the metallicity and molecule distribution in cold, dense clouds that may be gravitationally confined and represent precursor sites of star formation in DLAs.Dr. Jorgenson will also design an inquiry-based astronomy course for middle/high school students and teach the course via IfA's well-established HI STAR program. This program recruits native Hawaiians, underrepresented minorities, and students from low socioeconomic backgrounds to participate in week-long astronomy courses. The proposed course will emphasize the importance of Mauna Kea to astronomical research, vital outreach needed to maintain harmonious access to and possible further growth on the sacred mountain of Mauna Kea. In addition, at least three undergraduate students will be mentored as part of the NSF Research Experiences for Undergraduates program with particular attention paid to encouraging the participation of women and under-represented minorities in astronomy.