Model fitting AT20G ultra/hyper compact HII region visibilities and the nature of the 3mm excess

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Model fitting AT20G ultra/hyper Model fitting AT20G ultra/hyper compact HII region visibilities and compact HII region visibilities and

the nature of the 3mm excessthe nature of the 3mm excess

Ron EkersCSIRO

Sydney, Sep 8, 2010

Sep 2010 Ron Ekers 2

GalacticGalactic

Sample selection – AT20G (20GHz)– AT20G Galactic plane region (|b| < 1.5o)

– Blind survey

– S 20 GHz > 200 mJy

– 263 sources

Sample selection - MGPS-2 (0.843 GHz)– Compact in AT20G and MPGS-2

– Isolated in AT20G and MGPS-2

– Inverted spectrum (α 0.8-20GHz > 0.1)

– 46 sources

Murphy et al. 2010, MNRAS, 405, 1560

April 2010 Ron Ekers 5

Hyper Compact HII region Hyper Compact HII region G330-00G330-00

Ne 1.6x105

Size 0.05pc EM 1.3 109 Te 104 K

Low freq excess

3mm excess

April 2010 Ron Ekers 6

Compact galactic sourcesCompact galactic sourcesfree-free emission modelsfree-free emission models

Name Te Size EM Ne 95/45 Class

(K) (pc) (pc cm-6) GHz

G301.1366−00.2248 11600 0.02 3.0E+09 6.8E+05 ... H

G302.0321−00.0606 8000 0.14 3.0E+07 1.5E+04 1.6 UG307.5604−00.5875 7100 0.30 5.0E+06 4.1E+03 ... UG309.9217+00.4788 6700 0.03 8.0E+08 2.3E+05 2.0 HG323.4594−00.0788 8100 0.05 1.9E+08 6.4E+04 2.9

HG328.8076+00.6330 6400 0.25 6.0E+07 1.6E+04 2.5 UG330.9536−00.1820 10400 0.05 1.3E+09 1.6E+05 3.5 HG332.8254−00.5499 6500 0.06 4.0E+08 8.0E+04 1.8 U


G330 – UC/HC HII G330 – UC/HC HII


G330 – ATCA Visibility G330 – ATCA Visibility

G330 – 19GHz2.9” 5Jy

Vis

ibili

ty a

mp

litu

de

(Jy)

Spacing (kλ )


SED model fitting SED model fitting

Simple constant density free-free emission model Flux densities at 0.8, 19, 32, 44, 95 GHz Visibilities (angular sizes) at 19, (32, 44, 95) GHz Assume Te from recomb line 19GHz point gives EM and SED

– predicts all other frequencies– 0.8 GHz always high

» needs an optically thin large component

– 19, 32, 44 GHz usually fit– 95 GHz often high

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G330: 1x free-freeG330: 1x free-free

Fit EM at 19 GHz


G330: 2x free-freeG330: 2x free-free

Fit 0.8GHz


G330: free-free + dustG330: free-free + dust

Add dust Has to be

very hot


G330: G330: νν +1 +1 spectrum ?spectrum ?

ν +1 ?


G309 – ATCAG309 – ATCASize v FrequencySize v Frequency

20GHz 0.9” 40GHz 1.0” 95GHz 0.8”

– Getting the high frequency flux from the same size is a problem because it has to be optically thick at lower frequencies

– Easiest way to do this is to make filling factor <<1» Hierarchical model» Shell models

Note that the 0.8 GHz point can’t be fit in the same model

Model fitting AT20G ultra/hyper compact HII region visibilities and the nature of the 3mm excess

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