1. AT20G compact HII region Survey: Spitzer character of the sources in the MIR Martin Cohen, University of California/Berkeley “Hyper Compact HII regions” Workshop 8 September 2010

2. Outline What is the relationship betweenMIR/radio? Radio - ionized gas; MIR - PAHs in PDRs Matched-resolution (MOST) 843MHz & (MSX) 8.3  m Galactic Plane images Cohen & Green ratio: F (8.3  m)/S (843MHz) Thermal radio emission: median: 25±5 AT20G sources have at least three classes of MIR counterpart Cohen & Green 2001, MNRAS, 325, 531 Cohen et al. 2007, MNRAS, 374, 979

3. Extragalactic MIR countperparts 8  m absent or faint; 24  m well detected and planetary nebulae

4. GLIMPSE Benjamin et al. 2003 PASP, 115, 953 1983 1996 2004 45" 19" 1.7"b±1.1

5. Resolution & sensitivity changes: MSX  Spitzer IRAC for HII regions MSX 8.3  m IRAC 8.0  m 19GHz; 15” beam

6. How are MIR and radio related? Radio Mid-IR: MSX 8.3  m Radio (black) ionized gas; IR (white) hydrocarbon molecules in the PDR Radio: MOST 843MHz Far-IR emission from dust heated by the star

7. MIR morphology of HII regions 4.5 5.8 8.0  m 234 Ultra-compactCometary Compact HIICompact

8. Almost no MIR UC regions are found. Mostly small groups or pairs of compact and diffuse HII. IRAC false colours separate UC white (dust) emission from compact and diffuse yellow (PAHs) MIR/Radio = 42 Samples of the AT20G UCHII regions

9. An IRAC color-color plane H dH P Emphasizes PNe & HII regions F (8.3  m)/S (843MHz) Diffuse HII:median: 25 PNe median: 5 UC HII median: 42 HII compact: median: 140 (very small set)

10. Radio-MIR comparisons of groups (1) 1235-6302 1555-5243

11. Radio-MIR comparisons of groups (2) 1547-5448 1609-5154 H2?H2?

12. Hyper & Ultra compact MIR countperparts G301 H G309 H G323 H G332 U G302 U G307 U G328 U G330 H

13. Optical extinction along lines of sight Use deep silicate absorptions at 10,18  m