Dr. Lawrence Haffner and Dr. Ronald Reynolds, at the University of Wisconsin at Madison, along with Dr. Gregory Madsen at the Anglo Australian Observatory will move the Wisconsin H-Alpha Mapper (WHAM) instrument to a southern hemisphere site, and use it to survey the H-alpha emission from the southern sky over the course of 5 years. The end result, when combined with data from WHAM's northern survey, would be an all-sky survey at a resolution of one degree with a spectral resolution of 12 km/s over a 200 km/s window. The primary goal of the project is to advance our understanding of interstellar matter and processes within the disk and halo of the Milky Way. Ongoing WHAM observations also contribute to the fields of aeronomy, solar system astronomy, extragalactic astronomy, and cosmology. The project also provides opportunities for undergraduate and graduate student involvement, and delivers high-quality datasets for use by the entire astronomical community.
The Warm Ionized Medium (WIM) is an important constituent of the interstellar medium (ISM), the gas and dust between stars. Unlike opaque, dense, molecular gas from which stars form near the galactic plane, the WIM is a diffuse, atomic, ionized gas distributed in a thick layer (about 5,000 to 10,000 light-years from top to bottom) about the midplane that pervades most spiral galaxies similar to our own. Emission from this gas is enhanced in regions where star formation is most active, revealing a network of ionized material between the classical bright emission nebulae in the spiral arms of galaxies. The power needed to sustain such a layer is quite large. In the Milky Way, it requires an energy rate that is on the order of the mechanical output by all supernovae. From our vantage point within the Galaxy, the WIM pervades the whole sky. Its presence can be inferred from a variety of astronomical observations, but like classical emission nebulae is best studied through radiation emitted by free electrons and protons recombining briefly to a neutral hydrogen atom. One of the brightest of these "recombination" lines is Balmer-alpha (Hα), emitted at 656.3 nm in the red part of of the electromagnetic spectrum. Unlike nebulae, most WIM emission is produced at low rates in low-density gas that is difficult to detect with traditional instrumentation. To fully map the extent of the WIM, we built a dedicated instrument extremely sensitive to the large-scale, wide-spread Hα emission from the WIM. Sacrificing spatial resolution for the ability to record spectra—the distribution of light intensity versus wavelength—the Wisconsin H-Alpha Mapper (WHAM) has proved to be an exceptional tool. Its unique design is unsurpassed for collecting high-resolution optical emission-line spectra from diffuse sources. With the ability to detect emission nearly a billion times fainter than the Orion Nebula, WHAM can examine the faintest ionized emission regions in the local universe and tackle large-scale mapping projects quickly. After being built and tested in Wisconsin, WHAM spent 11 years (1997-2007) at Kitt Peak National Observatory in Arizona. From there it produced the first spectral Hα map of our Galaxy (the "WHAM Northern Sky Survey"). This publicly-released survey revealed details of the WIM for the first time comparable to other phases of the ISM. Researchers can now explore the global dynamics of the diffuse ionized gas throughout the Galaxy and local motions within nearby diffuse nebulae, bubbles, and superbubbles. On the largest scales, Galactic rotation along many lines of sight Doppler-shifts spatial regions into velocity groups that reveal the three-dimensional structure of the Galaxy. During this award period (2006-2012) we decommissioned WHAM at Kitt Peak; refurbished its aging hardware during a short maintenance visit in Wisconsin; and relocated it to Cerro Tololo in Chile. With observations resuming in 2009, data from the new southern site completes the first all-sky kinematic survey of this gas. The full survey allows a study of the extent and distribution of the WIM throughout the whole Galaxy. Observing then transitioned to an exploration of the physics of the WIM using WHAM to measure diagnostic emission lines from other elements, such as nitrogen, sulfur, and oxygen. By comparing emission from different elements and variations in different environments, we are able to probe the ionization state and temperature of the gas. Measuring these conditions throughout the Galaxy helps us discover the underlying processes that power the WIM. The southern hemisphere also provides us with a different view of unusual and distant clouds that are not co-rotating with the bulk of interstellar material. Using WHAM, we are tracing faint optical emission from these clouds to probe their characteristics as well. Discovering their origin and fate gives us rare insight into long-term evolution of galaxies and the intergalactic environment. In particular, we began several projects to explore the ionized component of the Magellanic Stream and Bridge, gas that has been tidally striped from our two largest Galactic companions. To date, these gas structures have only been mapped through their neutral component. As a mid-sized astronomical installation, WHAM has provided many opportunities to broaden its scientific and educational impact beyond its key science drivers. Although its primary mission is to explore diffuse ionized gas in the Milky Way, ongoing observations contribute significantly to the fields of aeronomy, solar system astronomy, extragalactic astronomy, and cosmology. Furthermore, the project provides rare opportunities for undergraduate and graduate students to regularly and directly interact with a research-grade astronomical observatory; pushes technological advances in remote observing techniques to improve the quality and efficiency of data collection; and delivers high-quality datasets for use by the entire astronomical community. Building on a well-established record, the relocation to the southern hemisphere has broadened the influence of the WHAM program and significantly increased opportunities for collaboration with this unique instrument.
