Measuring Interstellar Temperature and Ionization Variations Using Observations of Faint Diffuse [OII] Emission

PI Edwin Mierkiewicz

The interstellar medium (ISM) plays a vital role in the ongoing cycle of stellar birth and death as well as galactic evolution. However the role of interstellar matter, from how its properties are influenced by stars to how, in turn, its properties influence star formation is poorly understood.

Within the past decade substantial strides have been made towards unraveling the mysteries of a major ISM component, the widespread warm ionized medium (WIM). The advances were enabled by innovative spectroscopic techniques to detect and study extremely faint interstellar emission lines in the visible spectral region. With such observations it is possible to explore the connection between the Galactic disk and halo as energy and gas are transferred away from massive star-forming regions to large distances from the midplane. An especially exciting development in this area is the evidence for temperature variations and the existence of a previously unrecognized source of heating within the WIM. The emission line of ionized oxygen in the near ultraviolet spectral region (372.7 nm) is key to exploring variations in temperature and ionization state within the gas, and for investigating the role of this additional heating. Our [OII] observations will (1) provide the only opportunity to separate unambiguously variations in temperature from variations in ionization conditions in the warm ionized medium of our Galaxy and (2) confirm whether H-alpha, [NII], and [SII] data can provide reliable temperature information about diffuse ionized gas in our own and other galaxies.

Research Dates

01/01/2015 to 12/31/2025


  • Edwin Mierkiewicz
    Physical Sciences Department
    Ph.D., University of Wisconsin-Madison