Dr Martin Cohen (University of California, Berkley, USA)

Multiwavelength studies in the Galactic Plane with MSX and Spitzer - Dr Martin Cohen Colloquium

ATNF Marsfield Lecture Theatre

Abstract

The power of multiwavelength combinations of radio and optical data with infrared imagery from space can be applied to analyses of several different aspects of the interstellar medium along the Galactic Plane. The intimate association of photodissociation regions with HII regions implies the existence of a quantitative relationship between integrated fluxes of ionized domains in the mid-infrared and radio continuum. The ratio of 8.3-micron MSX flux to Molonglo 843-MHz continuum flux is a valuable tool that discriminates between thermal and nonthermal emission processes. These correlations are explored in a new study of HII regions using both MSX and the Spitzer GLIMPSE Legacy survey. Direct comparison of Spitzer 8.0-micron fluxes with MSX 8.3-micron fluxes for HII regions clearly reveals a problem with the diffuse calibration of IRAC. HII regions provide independent quantitative evidence for the discrepancy at 8.0 microns. However, IRAC imagery provides a unique perspective on the structure of HII regions and enables a search to be made for weakly ionized haloes of compact regions, akin to those suggested at radio wavelengths.

The Macquarie/AAO/Strasbourg H-alpha Planetary Nebula Catalogue (MASH)
contains 912 new planetary nebulae. An ongoing project comparing optical, radio, and mid-infrared attributes of all MASH nebulae has uncovered a unique object that represents a previously unobserved phase of stellar evolution. The 64 MASH nebulae that were observed in the GLIMPSE survey are being analyzed with the same broad wavelength philosophy.

NASA's mid-sized Explorer satellite, the Widefield Infrared Space
Experiment, is planned to launch in 2009. It will survey the whole sky with 500,000 times the sensitivity of COBE/DIRBE (at 3.3 and 4.7 microns) and 500 times that of IRAS (at 12 and 23 microns), and 80 times the areal resolution of MSX, offering an opportunity to study the entire plane in depth.