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

Outline• What is the relationship betweenMIR/radio?

• Radio - ionized gas; MIR - PAHs in PDRs

• Matched-resolution (MOST) 843MHz & (MSX) 8.3m Galactic Plane images Cohen & Green ratio: F(8.3m)/S(843MHz)

• Thermal radio emission: median: 25±5

• AT20G sources have at least three classes of MIR counterpart

Cohen & Green 2001, MNRAS, 325, 531Cohen et al. 2007, MNRAS, 374, 979

Extragalactic MIR countperparts

8m absent or faint; 24 m well

detected

and planetary nebulae

GLIMPSE Benjamin et al. 2003 PASP, 115, 953

1983

1996

2004

45"

19" 1.7"b±1.1

Resolution & sensitivity changes: MSXSpitzer IRAC for HII regions

MSX 8.3m

IRAC 8.0m19GHz; 15” beam

How are MIR and radio related?

Radio

Mid-IR: MSX 8.3m Radio (black) ionized gas; IR (white) hydrocarbon molecules in the PDR

Radio: MOST 843MHz

Far-IR emission from dust heated by the star

MIR morphology of HII regions 4.5 5.8 8.0m 234

Ultra-compact Cometary Compact

HIICompact CompactCompact

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

An IRAC color-color plane

HdH

P

Emphasizes PNe & HII regions

F(8.3m)/S(843MHz)Diffuse HII:median: 25PNe median: 5 UC HII median: 42 HII compact: median: 140 (very small set)

Radio-MIR comparisons of groups (1) 1235-6302

1555-5243

Radio-MIR comparisons of groups (2)

1547-5448

1609-5154

H2?

Hyper & Ultra compact MIR countperparts

G301 H G309 H G323 H

G332 UG302 U G307 U G328 U

G330 H

Optical extinction along lines of sight• Use deep silicate absorptions at 10,18 m