Study of warm/diffiused ionized gas using SALT

Project Description:

The Wisconsin Hα Mapper (WHAM) mapped the Milky Way in Hα wavelengths, uncovering areas of star formation as well as warm, diffuse ionized gas (DIG), referred to as the Reynolds Layer. The DIG is distributed in a much thicker layer compared to the star-forming disc. Such distribution is found to be typical, as seen in several edge-on late type galaxies. DIG regions have emission-line flux ratios that are distinct from star forming regions as well as AGN. While the gas itself likely comes from a confluence of star-formation-region fountains (outflows) from disc midplanes, in-situ mass-loss from evolved stars in thick discs, and infall from high-velocity clouds, the ionization mechanisms are debated. Leakage of ionizing photons from mid-plane star-formation is one possibility, while in situ photo-ionization from hot evolved stars (metal-poor blue horizontal-branch or pAGB stars) is another. Shocks may be another ionization source. One way to probe these ionization sources is by targeting DIG regions at (i) varying distances from star-forming regions and at (ii) varying heights about the mid-plane with known gradients in evolved stellar populations. These lines of sight will be carefully chosen to be outside the solar circle where velocity information yields unique velocity-to-distance transformation. By examining the trends in ionization conditions in the DIG with HII region distance and mid-plane height, including line diagnostics sensitive to shock heating, we will be able to determine uniquely the contributions from different sources of DIG ionization. The first version of the Slit Mask Integral Field Unit (SMI-200) has recently gone through a successful engineering commissioning run on the Southern African Large Telescope. The SMI-200 is a front end module for the visible arm or Robert Stobie Spectrograph (RSS) on board SALT. The module reformats an 18”x23” sky patch sampled at 0.9” onto the spectrograph slit input using optical fibers. The elongated hexagonal shape of SMI is ideal for observing galaxies over a range of inclination angles, and can be used to map more extended objects from Galactic HII regions. Using the proprietary SALT data for SMI-200, we aim to probe the source of ionization of DIG regions from emission line identifiers.

Research Area:

Astronomy

Project Level:

Masters

This Project Is Offered At The Following Node(s):

(UCT)(NWU)