Observing the metallicity and star formation history of galaxies since the earliest times in the universe is crucial to understanding galaxy formation and evolution. Theory suggests that metallicity changes less rapidly than star formation rate as a function of redshift, but there is no firm observational foundation for the cosmic metallicity history of star-forming galaxies. To address this, Dr. Lisa Kewley (University of Hawaii) will carry out a program to gain a simultaneous understanding of the metallicity and star formation history of galaxies between 0 < z < 3. This research builds upon the foundation laid by Dr. Kewley for diagnosing and interpreting the metallicity and star-formation properties of galaxies. The observations to be carried out in this program will: (1) impact the use of Gamma-Ray Burst (GRB) hosts as tracers of star formation and metallicity to high redshifts by determining the relationship between GRB hosts and the general galaxy population, (2) uncover the relationship between metallicity and large-scale structure using the unprecedented large area and completeness of new intermediate redshift surveys, and (3) provide a solid observational understanding of the cosmic metallicity and star formation history of galaxies. The observed metallicity history will be compared with predictions from semi-analytic models and cosmological hydrodynamic simulations, providing a critical test of our current theoretical understanding of galaxy formation and evolution.
This research will be incorporated into the University of Hawaii Active (inquiry-based) Learning Astronomy 110 class being developed by Dr. Kewley to engender an understanding of Hawaii's past and present role in astronomy. The research program will also be integrated into the University Hawaii Student/Teacher Astronomy Research (HI STAR) program, which targets years 9-12 native Hawaiian or other minority students from low socioeconomic backgrounds. Dr. Kewley will develop for the HI STAR program a spectroscopy lab and galaxy evolution project and, with her research group, will mentor HI STAR students for Science Fair projects using spectra obtained as part of the research program. By promoting a solid understanding of spectroscopy and sharing the excitement of astronomical discovery, this program aims to strengthen the physics and astronomy background of underprivileged students in Hawaii, and motivate them to pursue a career in science.
In the very early universe, gas clouds clumped and condensed to form the first stars. These gas clouds collided, forming larger and larger galaxies across cosmic time. During each collision, new generations of stars were born, providing a glowing signpost for galaxy evolution, and creating almost all of the elements heavier than Helium, the building blocks of life. The elements transform the way new stars are born and evolve, the way planets are formed around young stars, the way stars explode and die, and the way stars assemble into new galaxies. Therefore, simultaneously tracing the star formation and chemical elements back to the earliest times in the universe provides our most powerful method of unveiling the birth and growth of galaxies. We tracked the chemical history of galaxies like our Milky Way from just 4 billion years after the Big Bang to the present day. We combined optical and infrared observations using new instrumentation on the Keck and Subaru telescopes on Mauna Kea. We showed that galaxies became enriched with the elements during their first few billion years and that they have been only slowly accumulating elements ever since. We compared our results with state-of-the-art theoretical models of galaxy formation and evolution that include the evolution of the elements and hydrodynamics. We showed that the most massive galaxies have less elements than predicted by the models. We used a novel technique called gravitational lensing to probe the most distant galaxies observable with modern spectrographs. Einstein predicted that the gravity from massive structures in the universe would be so strong that it would bend light, creating a telescope as large as galaxies, or clusters of galaxies. These galaxy clusters act as giant lenses, magnifying and stretching the light from background distant galaxies, allowing us to observe galaxies within a 1/10th the age of the universe. Using gravitational lensing, we measured the spread of oxygen within the first known spiral galaxy, just 4 billion years after the Big Bang. Our oxygen measurements suggest that galaxies form "inside-out", first assembling halos around compact dense cores, with the outer regions being built up over the subsequent 10 billion years through galaxy mergers or infall of gas from the surrounding medium. We investigated the use of galaxies that host gamma-ray bursts as possible probes of star formation in the very early universe. Gamma-ray bursts are some of the most poweful explosions known to man. They are incredibly luminous, providing a bright landmark for the presence of distant galaxies. We showed that gamma-ray bursts occur in galaxies that are more pristine than normal galaxies, but that they may probe normal star-forming galaxies in the very distant universe.
