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

Jorgenson, Regina A

Investigators

Abstract

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 z>2 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.