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Compact HII regions toward Methanol Maser traced sources of Massive Star Formation

Compact HII regions toward Methanol Maser traced sources of Massive Star Formation. Adam Avison (UK ARC, JBCA) Gary Fuller + MMB Collaboration. Overview. HII Regions in sites of MSF The MMB Survey MMB Continuum sources characterisitcs Size differences as evolutionary indication Conclusion.

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Compact HII regions toward Methanol Maser traced sources of Massive Star Formation

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  1. Compact HII regions toward Methanol Maser traced sources of Massive Star Formation Adam Avison (UK ARC, JBCA) Gary Fuller + MMB Collaboration

  2. Overview • HII Regions in sites of MSF • The MMB Survey • MMB Continuum sources characterisitcs • Size differences as evolutionary indication • Conclusion YERAC 18/07/2011

  3. HII Regions in sites of MSF • Only massive stars are capable of creating embedded HII region making them unique tracers of massive star formation. • Ultra Compact HII regions are created as a forming massive star begins ionising the hydrogen in its surrounding natal cloud. • Hyper Compact HII regions form prior to UCHII and are studied as a separate class of object potentially created as either outflow cavities or the accretion disks are photoionized. Values from Kurtz 2002. YERAC 18/07/2011

  4. The Methanol MultiBeam Survey • The MMB survey was an Anglo-Australian collaboration which surveyed the galactic plane for class II methanol masers at 6.67GHz. • The survey region was:l = -174° < l < 60° |b| < 2° and was conducted using the Parkes radio telescope. • The class II CH3OH maser is uniquely associated with sites of massive star formation (Minier et al 2003). • ~350 new maser sources were detected during the survey. YERAC 18/07/2011

  5. High Resolution MMB Observations • Using ATCA all newly detected masers were observed to give high resolution positions. • Correlator setup to simultaneously observe at ~6GHz and 8GHz • The 8GHz observations were used to look for HII regions in the same field as CH3OH maser sources. • Of the 414 maser sources in the MMB-ATCA data 105 sources were found at 8GHz. YERAC 18/07/2011

  6. Associated Objects? The obvious question to initially ask about these sources is are the Masers and HII regions associated? Naively: “Some but not all” 1’’ @ 5kpc = 0.02pc 1000” @ 5kpc = 24pc YERAC 18/07/2011

  7. Characterizing Sources • The sources were fit as 2D Gaussians with MIRIAD task IMFIT and the integrated flux densities calculated. • 83 HII regions were well fitted, with the remainder were show extended morphologies. • From these fits or averaged radial sizes we calculated source diameters. YERAC 18/07/2011

  8. Characterizing Sources : The Devil is in the Distance Sources with <10” separations from masers distance used are from (Green & McClure-Griffiths 2011 in prep). Remaining sources used the near/far kinematic distances (Green 2008). Distance ambiguity! We used a couple of techniques to try and overcome this. YERAC 18/07/2011

  9. Characterizing Sources:Basic Emission Measures A simplistic emission measure was calculated for each source: Which was then used to further characterize sources. YERAC 18/07/2011

  10. MMB HII region types • Ever so slightly subject to change. • See A.Avison et al. 2011 in prep. YERAC 18/07/2011

  11. Evolutionary Traits From the Evolutionary time lines of e.g. Breen et al. 2010 one would expect HII regions associated with masers to be smaller in size than those with greater maser/continuum separation. This effect has been seen by e.g. Walsh et al. 1998 & Ellingsen et al. 2005. Breen et al. 2010 YERAC 18/07/2011

  12. K-S Testing for size differences Distance dependent Distance independent Compared integrated-to-peak flux ratio for same split: p-value: 0.4158 • Comparison of diameters for objects with separations of ≤2” and >2” at both distances. • p-values:0.5314(near) / 0.6022(far) RandomDistances • Using a galactic HII region distribution derived from 354 sources (Caswell & Haynes 1987; Kolpak et al. 2003; Fish et al. 2003; Sewilo et al. 2004; Thompson et al. 2006) each HII region was randomly assigned a distance and the distance dependent test repeated. • 10,000 iterations were conducted and only 1.5% of them show any difference between the ≤2” and >2” groups. YERAC 18/07/2011

  13. Conclusions • 105 8GHz continuum sources in the MMB-ATCA data • We categorize them as 12 HCHII, 14 UCHII and 48 HII with 31 still confused. • No size differences seen between associated and large separation sources. Not entirely surprising. Things I haven’t said… • GLIMPSE characteristics of these sources have been derived. • Interesting velocity information has been seen in the MMB masers themselves. YERAC 18/07/2011

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