The Four-Star Galaxy Evolution (FourGE) Survey will identify, catalog, and measure the cosmological redshifts of approximately 10,000 galaxies, using the new Four-Star wide-field near-infrared imaging camera on the 6.5-meter Magellan telescope. The Principal Investigator, co-Principal Investigator, and the postdoctoral researcher and graduate student supported by this award will, over the course of 30 observing nights on Magellan, obtain deep imaging of six different sky fields using five custom-built medium-band filters. These filters have been designed to accurately constrain redshifts (z) of galaxies in the range 1.5 < z < 3.5. The depth of the imaging will detect galaxies as small as those likely to be the precursors of present-day galaxies the size of the Milky Way. The redshift precision will be sufficient to trace the underlying large-scale structure marked by galaxies and substantially reduce the uncertainties in star formation rates and the total mass contributed by stars. By targeting this range of redshifts, the survey focuses on the phase of cosmological history when star formation and the growth of galaxies and active galactic nuclei (AGN) were at their peak. By coupling the survey data with archival X-ray data, the team plans to measure the growth of the stellar masses of galaxies in different environments; to constrain the role of AGN in halting star formation; and constrain theories of galaxy formation through comparison with large-scale simulations. In addition to professional training and mentoring of the postdoctoral fellow and graduate student, the project will support a range of broader impacts including release of the survey data to the community through the Virtual Astronomical Observatory, involvement of undergraduate students from under-represented groups, and the use of survey data in undergraduate classes and public presentations, as well as contributing to the early-career development of two women researchers.
Intellectual Merit: The primary outcomes of our FourStar Galaxy Evolution (ZFOURGE) Survey has been to increase the base of knowledge on how galaxies like our own Milky Way acquire their cold gas, convert this gas into stars, and assemble into the rich diversity of structures in the Universe. ZFOURGE targeted the progenitors of present-day galaxies during a critical epoch for galaxy formation, during the time spanned by redshifts 1.5 < z < 3.5. Professors Papovich and Tran at Texas A&M University and their team of international collaborators surveyed deeply three fields on the sky, with new near-Infrared filters with the FourStar instrument on the Magellan 6.5 meter telescope, to measure accurate redshifts of more than 30,000 galaxies, including galaxies with masses of the precursors of Milky-Way-sized galaxies. The rich dataset provided from the ZFOURGE survey will provide a lasting resource for research astrophysicists to study the Universe. The impact will be long term as there are no planned surveys for the next 5-10 years that will surpass the quality of our data. ZFOURGE has provided new results on several topics, covering two main themes. The first theme is to show how galaxies like the Milky Way formed their stars and assembled them into their present configurations. ZFOURGE has shown that galaxies like the Milky Way were smaller by a factor of 10 in mass and size 10 billion years ago. The main period of star-formation in these galaxies occurred in the distant past, and at present, galaxies like the Milky Way are forming stars at a rate lower by a factor of 30 compared to their peak rate about 8 billion years in the past. Our own Sun was formed at a time when galaxies like the Milky Way were finishing its major period of star-formation. ZFOURGE has also shown that the distribution of mass in galaxies has grown steadily over time, and has measured the rate at which galaxies have ceased to form new stars. One result is that a population of low-mass galaxies that cease to form stars increases as the Universe ages, and this appears to be a result of galaxies ceasing to form stars as they become satellites of more-massive galaxies. One of the other results from ZFOURGE is to understand why some galaxies cease to form stars while others continue to be star-forming, even when the galaxies have the same mass. ZFOURGE showed that in the distant Universe (studied at redshifts 1 < z < 3), galaxies that have ceased to form stars have more satellite galaxies, which implies that these primary galaxies have larger amounts of dark-matter. Why this affects the star-forming properties of galaxies remains an open question for further investigation. The second theme from ZFOURGE has been to show that there exists a significant population of galaxies with large amounts of mass, and that an interesting fraction of them had formed most of their stars already within those first two billion years of the Universe. The rapid formation timescales pose challenges to our theoretical understanding of galaxy assembly, and this will lead to further investigations for the next decade. Broader Impacts: The ZFOURGE team has been committed to expand the scientific literacy of the general public, students, and researchers. The team provided materials for use in public science talks, educational resources to use in undergraduate and graduate courses in astronomy and astrophysics. The ZFOURGE team is diverse and has improved the scientific literacy of underrepresented groups in the sciences. As of December 2014, the ZFOURGE survey has generated 7 refereed publications with several more results to be published in 2015. All publications and project details are accessible on the dedicated website zfourge.tamu.edu. The ZFOURGE data products (images and multiwavelength catalogs) will be available to the public in 2015. The data products have already been used, and will continue to be used, to support undergraduate research experiences for undergraduates.
