The role of spiral arms in the star-formation process

When looking at external, grand design galaxies, spiral arms topology and star formation are observed to be closely linked. However, it’s unclear whether the spiral arms are triggering one or more of the star formation stages or simply collecting and organising the star-forming material. The main stages of star formation are represented by the conversion of atomic gas to molecular clouds, molecular clouds with internal dense clumps and the clumps forming cores from which the single stars form.

Eden et al., 2012, MNRAS, 422, 3178; Eden et al., 2013, MNRAS, 431, 1587; Eden et al., 2015, MNRAS, 452, 289; Ragan et al., 2016, MNRAS, 462, 3123; Ragan et al., 2018, MNRAS, 479, 2361

High-mass star formation

High-mass stars are vitally important to the evolution of their host galaxies and the formation of future generations of stars. However, very little is known about the environments in which these massive stars form. There are multiple processes that a high-mass star undergoes in its formation. When a pre-stellar clump begins to collapse, protostars heat the local environment, exciting a methanol maser. As well as this, the protostar is swelling and contracting, a process that is observable through massive young stellar objects. The presence of a high-mass star is also determined through the detection of a Hii region.

Urquhart et al., 2013, MNRAS, 435, 400; Urquhart et al., 2015, MNRAS, 446, 3461; Urquhart et al., 2015, MNRAS, 452, 4029; Eden et al., 2018, MNRAS, 477, 3369

Galactic Plane Surveys

The most effective way to study large numbers of star-forming environments across differing evolutionary stages, Galactic locations, local environments is to get a large sample that becomes statistically significant. The method to do this is to use Milky Way-wide surveys which are now possible due to the improvement and advancement of telescope facilities and instruments. These Galactic Plane surveys include different tracers and different stages of star formation, from molecular clouds, to star-forming clumps in the sub-millimetre, to young stellar objects in the far-infrared.

Urquhart et al., 2013, MNRAS, 435, 400; Urquhart et al., 2015, MNRAS, 452, 4029; Moore et al., 2015, MNRAS, 453, 4264; Rigby et al., 2016, MNRAS, 456, 2885; Molinari et al., 2016, A&A, 591, 149; Eden et al., 2017, MNRAS, 469, 2163; Elia et al., 2107, MNRAS, 471, 100; Urquhart et al, 2018, MNRAS, 473, 1059

Planck Galactic Cold Clumps

In the process of measuring the anisotropy of the cosmic microwave background radiation, Planck mapped the cold dust within the Milky Way as the higher frequency channels cover the peak thermal emission frequencies of dust colder than 14 K. In the Galactic emission, nearly 14,000 sources were identified, covering the whole sky from the Galactic Plane to high-latitude clouds. These sources have low temperatures (6-20 K), small velocity widths and are quiescent, not affected by ongoing star formation. This makes them a prime target for studying the very earliest star formation.

Liu et al., 2018, ApJS, 234, 28; Juvela et al., 2018, A&A, 612, 71; Tang et al., 2018, ApJ, 856, 141; Liu et al., 2018, ApJ, 859, 151; Zhang et al., 2018, ApJS, 236, 49; Yi et al., 2018, ApJS, 236, 51

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