The Galaxy Champagne
Nicolas Flagey

Over 400 small (a few 10") rings, disks and shells have been discovered from visual inspection of the Spitzer /MIPSGAL 24 um mosaic images. These MIPSGAL bubbles (MBs) are pervasive through the entire Galactic plane in the mid-infrared. They span a large range of morphologies, sizes and fluxes. The analysis of near- to far-IR broadband images has unveiled that 54 MBs (about 13%) have central sources at 24 um while this number rises to at least 100 in the IRAC or 2MASS images. The extended emission is detected in about two thirds of the MBs at 70um but less than one third at any other IR wavelengths. When we published the catalog, only 15% of the MBs were identified or associated with stars of known spectral types. Most of the known MBs were associated with planetary nebulae while a few were supernova remnants, Wolf-Rayet stars (WR), luminous blue variables (LBV) and other emission line stars. The MBs are thus suspected to be associated with stars in their late stages of evolution, with at least a fraction of them being massive. In this talk, I will address the two main questions arising from this discovery: (1) what are the MBs? and (2) what is the origin of their emission? I will first present the catalog of the MBs and their general properties, in terms of morphologies, sizes, and broadband fluxes. In particular, I will show that mid to far-IR observations from the Spitzer and Herschel Galactic plane surveys provide a direct measurement of the dust mass ejected by the MBs. Then, I will detail some of the many follow-up observations we obtained to identify the origin of the mid-IR emission and the nature of the unknown objects. I will focus on: (1) unique mid to far-IR (Spitzer, Herschel) observations that lead to the discovery of several highly excited, dust poor planetary nebulae, and several dust rich, massive star candidates; and (2) Palomar and VLT near-IR observations of central sources in MB, that reveal a large number of new massive stars. I will discuss other paths we are exploring, from radio to optical. I will summarize the results of these investigations and discuss their relevance for the complete catalog.