The Bubbling Galactic Disk

AvisualexaminationoftheimagesfromtheGalacticLegacyInfraredMid-PlaneSurveyExtraordinaire(GLIMPSE) has revealed 322 partial and closed rings that we propose represent partially or fully enclosed three-dimensional bubbles. We argue that the bubbles are primarily formed byhot young stars in massive star formation regions. We have found an average of about 1.5 bubbles per square degree. About 25% of the bubbles coincide with known radio H ii regions, and about 13% enclose known star clusters. It appears that B4-B9 stars (too cool to produce detectable radio H ii regions) probably produce about three-quarters of the bubbles in our sample, and the remainder are produced by youngO-B3starsthatproducedetectableradioHiiregions.Someofthebubblesmaybetheouteredgesof Hiiregions wherePAHspectralfeaturesareexcitedandmaynotbedynamicallyformedbystellarwinds.Onlythreeof thebubbles areidentifiedasknownSNRs.NobubblescoincidewithknownplanetarynebulaeorW-RstarsintheGLIMPSEsurvey area. The bubbles are small. The distribution of angular diameters peaks between 10 and 30 with over 98% having angular diameters less than 100 and 88% less than 40. Almost 90% have shell thicknesses between 0.2 and 0.4 of their outer radii.Bubbleshell thicknessincreasesapproximately linearlywithshell radius. Theeccentricitiesare ratherlarge, peaking between 0.6 and 0.7; about 65% have eccentricities between 0.55 and 0.85. Subject headinggs: H ii regions — ISM: bubbles Online material: extended color figure, machine-readable tables