Wednesday 20 Feb 2019[Seminar] Statistical Shape Analysis and Classification of Galactic HII Regions

Justyn Campbell-White - University of Kent

4th Floor, Physics Building 14:00-15:00

We present here our shape analysis method for a sample of 76 Galactic HII regions from MAGPIS 1.4 GHz radio data, and a selection of synthetic observations of HII regions, complementary to the observed sample. The main goal is to determine whether physical properties and initial conditions of massive star cluster formation are linked to the shape of the regions. We outline a systematic procedure for extracting region shapes and perform hierarchical clustering on the shape data, in order to identify such physical and morphological associations.
For the MAGPIS data, we identified six groups that categorise HII regions by common morphologies. We confirmed the validity of these groupings by bootstrap re-sampling and the ordinance technique multidimensional scaling. We then investigated associations between physical parameters and the assigned groups. Location is mostly independent of group, with a small preference for regions of similar longitudes to share common morphologies. The shapes are homogeneously distributed across Galactocentric distance and latitude. One group contains regions that are all younger than 0.5 Myr and ionised by low- to intermediate-mass sources. Those in another group are all driven by intermediate- to high-mass sources. One group was distinctly separated from the other five and contained regions at the surface brightness detection limit for the survey.
For the synthetic data, we have so far considered one set of initial conditions and find that the simulations produce well representative observations that are indistinguishable from the observed sample by our shape analysis method. The method readily groups regions of differing evolutionary stages. We find that the assigned shape groupings are more susceptible to different noise profiles than different projections. Future applications of this shape analysis procedure include incorporating different wavelength observations of HII regions and considering other diffuse astronomical objects such as supernova remnants.

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