Nia Imara, Ph.D.
Title "The Origin of Stellar Nurseries"
Abstract: All stars are observed to form in giant molecular clouds (GMCs), thousands of which exist in the Milky Way and other galaxies. Given that molecular cloud and stellar evolution are closely interconnected, we would like to better understand how GMCs form and evolve.
In this presentation, I will discuss observations of GMCs showing that these star-forming structures sometimes have systematic linear velocity gradients. To address the question of the origin of the gradients – and to touch on the question of GMC evolution – I will present a detailed analysis comparing the velocity fields of molecular clouds and the atomic hydrogen (HI) surrounding them. I used CO and 21-cm observations to make first-moment velocity maps of the molecular clouds and associated HI. For GMCs in the Galaxy and M33, my key finding is that the gradient position angles of HI and the associated GMCs are generally not aligned. Thus, if the linear velocity gradients in GMCs are caused by rotation, their angular momentum is much less than that predicted by formation scenarios in which GMCs collapse from the surrounding interstellar medium. Time permitting, I will also present an extinction map showing the distribution of molecular gas in the Large Magellanic Cloud. The advantage of using extinction mapping – an alternative method for inferring the distribution of molecular gas – is that no assumptions need to be made regarding the virialization or the shapes of molecular clouds. Furthermore, extinction mapping is capable of detecting H2 in regions where CO is undetectable, either because CO does not exist or because CO observations are not sensitive enough.
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