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1 Model fitting AT20G ultra/hyper compact HII region visibilities and the nature of the 3mm excess Ron Ekers CSIRO Sydney, Sep 8, 2010
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Sep 2010Ron Ekers2 Galactic n Sample selection – AT20G (20GHz) –AT20G Galactic plane region (|b| < 1.5 o ) –Blind survey –S 20 GHz > 200 mJy –263 sources n 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 n Murphy et al. 2010, MNRAS, 405, 1560
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3 Survey Source Density v Galactic Latitude 0.8 o
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4 Ultra Compact HII Regions n 46 galactic sources with rising spectra and S 20 >0.2JY –6 extragalactic, 2 planetary nebula, 38 UC HII, 3-5 HC HII G301 1235-6302 GLIMPSE 3-colour image GLIMPSE 8µm image 20GHz contours
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April 2010Ron Ekers5 Hyper Compact HII region G330-00 n Ne 1.6x10 5 n Size 0.05pc n EM 1.3 10 9 n Te 10 4 K n Low freq excess n 3mm excess
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April 2010Ron Ekers6 Compact galactic sources free-free emission models Name Te SizeEM Ne 95/45 Class (K) (pc)(pc cm -6 ) GHz G301.1366 − 00.224811600 0.02 3.0E+09 6.8E+05... H G302.0321 − 00.0606 8000 0.14 3.0E+07 1.5E+04 1.6 U G307.5604 − 00.5875 7100 0.30 5.0E+06 4.1E+03... U G309.9217 + 00.4788 6700 0.03 8.0E+08 2.3E+05 2.0 H G323.4594 − 00.0788 8100 0.05 1.9E+08 6.4E+04 2.9 H G328.8076 + 00.6330 6400 0.25 6.0E+07 1.6E+04 2.5 U G330.9536 − 00.182010400 0.05 1.3E+09 1.6E+05 3.5 H G332.8254 − 00.5499 6500 0.06 4.0E+08 8.0E+04 1.8 U
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Sep 2010Ron Ekers7 G330 – UC/HC HII
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Sep 2010Ron Ekers8 G330 – ATCA Visibility G330 – 19GHz 2.9” 5Jy Visibility amplitude (Jy) Spacing (kλ )
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Sep 2010Ron Ekers9 SED model fitting n Simple constant density free-free emission model n Flux densities at 0.8, 19, 32, 44, 95 GHz n Visibilities (angular sizes) at 19, (32, 44, 95) GHz n Assume Te from recomb line n 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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8 Sep 2010Ron Ekers10 G330: 1x free-free n Fit EM at 19 GHz
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8 Sep 2010Ron Ekers11 G330: 2x free-free n Fit 0.8GHz
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8 Sep 2010Ron Ekers12 G330: free-free + dust n Add dust n Has to be very hot
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8 Sep 2010Ron Ekers13 G330: ν +1 spectrum ? n ν +1 ?
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8 Sep 2010Ron Ekers14 G309 – ATCA Size v Frequency n 20GHz 0.9” n 40GHz 1.0” n 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 n Note that the 0.8 GHz point can’t be fit in the same model
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April 2010Ron Ekers15 UC and HC HII regions from AT20G survey
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