1. 1 Model fitting AT20G ultra/hyper compact HII region visibilities and the nature of the 3mm excess Ron Ekers CSIRO Sydney, Sep 8, 2010

2. 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

3. 3 Survey Source Density v Galactic Latitude 0.8 o

4. 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

5. 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

6. 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

7. Sep 2010Ron Ekers7 G330 – UC/HC HII

8. Sep 2010Ron Ekers8 G330 – ATCA Visibility G330 – 19GHz 2.9” 5Jy Visibility amplitude (Jy) Spacing (kλ )

9. 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

10. 8 Sep 2010Ron Ekers10 G330: 1x free-free n Fit EM at 19 GHz

11. 8 Sep 2010Ron Ekers11 G330: 2x free-free n Fit 0.8GHz

12. 8 Sep 2010Ron Ekers12 G330: free-free + dust n Add dust n Has to be very hot

13. 8 Sep 2010Ron Ekers13 G330: ν +1 spectrum ? n ν +1 ?

14. 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

15. April 2010Ron Ekers15 UC and HC HII regions from AT20G survey