A Systematic Search for Stars in Almost-Dark Galaxies

Indiana University, Bloomington IN

Investigators

Abstract

Galaxies are collections of stars, gas, dust, and dark matter, all held together by gravity. It is nearly 100 years since American Astronomer Edwin Hubble first showed that galaxies are island universes, containing of billions of stars. The investigators seek to understand how galaxies form and change over time. Their goal is identifying the star formation processes that produced the wide variety of galaxies observed. The investigators have selected for special study a set of nearby, gas-rich, galaxies. These galaxies were found with the Arecibo radio telescope. These galaxies contain large amounts of neutral hydrogen (HI) gas, the raw ingredient of new generations of stars. Furthermore, graduate and undergraduate students who work on the project will receive professional development and training in scientific research, technical and mathematical methods, image processing and analysis, and computer programming. The ALFALFA survey is a HI survey aimed at constructing a statistically-complete census of neutral hydrogen gas in the local universe. ALFALFA covers 7000 square degrees of sky and has cataloged 30,000 objects. This project aims to measure the optical properties of two specific types of ALFALFA sources: Ultra-Compact High Velocity Clouds (UCHVCs), which are neutral hydrogen gas clouds with properties that make them good candidates for nearby low-mass galaxies, and "Almost-Dark" galaxies, which are HI sources with a wider range of possible distances and masses. Both classes of objects have no clear optical counterpart in existing catalogs, so the objective is to detect and characterize the optical emission from these objects in order to better understand their properties and evolutionary state. To accomplish this objective, the investigator and her students will obtain and analyze deep, wide-field, optical imaging with the WIYN 3.5-meter telescope and One Degree Imager (ODI) of a well-defined sample of UCHVCs and Almost-Dark galaxies chosen from ALFALFA. The observations will be used to investigate the properties of the UCHVC and Almost-Dark samples and address important questions about how galaxies with neutral gas form and evolve. These questions include: What implications do the UCHVCs have for the ``missing satellites problem''? What fraction of the UCHVCs have detectable stellar populations? Are there correlations between the galaxies' environments and locations within the Local Volume and their properties (e.g., the presence or absence of ongoing star formation, their evolutionary phase)? What is the nature of the Almost-Dark galaxies, and how do their properties differ from ``normal'' galaxies in optical catalogs? What do the Almost-Dark objects reveal about how star formation takes place in galaxies at the extreme end of the HI mass to optical luminosity regime? The objects in the UCHVCs sample can also be used to help characterize the Baryonic Tully-Fisher Relation down to very low galaxy masses (less than ten million solar masses) and to probe the chemical evolution of the Universe. The investigator has made major commitments to the support and mentoring of graduate and undergraduate students, and to the training of students in research. The investigator will also work with consultants at the Indiana University Center for Innovative Teaching and Learning to revise a large introductory astronomy course for non-majors. The investigator will use the data taken with optical and radio telescopes in a course to pique student's interest, help illustrate the concepts being taught, and show concrete examples of how modern research is done in astronomy. Finally, the investigator will work on advancing science outreach and education through her membership on the Board of Directors of the Maria Mitchell Association, a non-profit research, education, and outreach organization that promotes the legacy of America's first female professional astronomer.