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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
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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
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Extragalactic MIR countperparts
8m absent or faint; 24 m well
detected
and planetary nebulae
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GLIMPSE Benjamin et al. 2003 PASP, 115, 953
1983
1996
2004
45"
19" 1.7"b±1.1
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Resolution & sensitivity changes: MSXSpitzer IRAC for HII regions
MSX 8.3m
IRAC 8.0m19GHz; 15” beam
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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
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MIR morphology of HII regions 4.5 5.8 8.0m 234
Ultra-compact Cometary Compact
HIICompact CompactCompact
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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
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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)
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Radio-MIR comparisons of groups (1) 1235-6302
1555-5243
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Radio-MIR comparisons of groups (2)
1547-5448
1609-5154
H2?
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Hyper & Ultra compact MIR countperparts
G301 H G309 H G323 H
G332 UG302 U G307 U G328 U
G330 H
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Optical extinction along lines of sight• Use deep silicate absorptions at 10,18 m