Seeking the Lost Interstellar Medium of Red-Sequence Galaxies

Cooksey Kathy L, Santa Cruz CA

Investigators

Abstract

Dr. Kathy Cooksey is awarded an NSF Astronomy and Astrophysics Postdoctoral Fellowship to carry out a program of research and education at the Massachusetts Institute of Technology Kavli Institute for Astrophysics and Space Research (MKI). In a typical galaxy color-magnitude diagram, there are two clear populations: a distinct red sequence and a diffuse blue cloud. The red-sequence galaxies (RSGs) generally have elliptical or spheroidal morphologies, have little or no neutral interstellar medium (ISM), and are not actively forming stars. RSGs tend to be more massive than the star-forming spiral galaxies that constitute the blue cloud. A crucial step to making massive, "red and dead" elliptical galaxies is to halt star formation, which allows the galaxies to evolve onto the red sequence. One of the likely mechanisms that would shut down star formation is the expulsion of the gas entirely from the galaxy through galactic feedback processes. To understand how RSGs lose their ISM, Dr. Cooksey will conduct a two-pronged attack: (1) probe the halos of a variety of red-sequence galaxies with quasar absorption-line spectroscopy in search of T~10,000 K gas--the expelled ISM; and (2) characterize the ages, stellar abundances, environment, and nuclear activity of the galaxies that do and do not have gaseous halos. A diverse sample of 50 RSG-quasar pairs at redshifts 0.25<z<0.5 will be surveyed with the Inamori-Magellan Areal Camera & Spectrograph and the Magellan Echellette Spectrograph, two complementary instruments that allow for an efficient survey of the galaxies and quasars, respectively. Analysis will include correlating galaxy and halo-gas properties and applying the results to distinguish between different feedback mechanisms. Dr. Cooksey will also design and teach an inquiry-based astronomy course for students traditionally under-represented in the sciences. The MKI Education and Outreach Group will assist in the recruitment of under-served middle- and high-school students for this course, which will be run through the High School Studies Program of the MIT Educational Studies Program. The students will also be taught about current issues of diversity and equity in the sciences (e.g., stereotype threat) and about strategies to overcome them (e.g., malleable mind-set).