2024.03.21 - William Henney
Channel: Coloquio IRyA
Date: 2024-03-22

Speaker info: Dr. William Henney, IRyA-UNAM
https://www.irya.unam.mx/gente/w.henney/

Title: Order and disorder in photoionized regions
Abstract:
What drives the dynamics of H II regions? Is it simple expansion, or 
something more complicated? How does it vary between compact single-star regions on sub-parsec scales and giant regions powered by massive star clusters on scales of hundreds of parsecs? I will discuss how studying 
the dependence on plane-of-sky separation of fluctuations in line-of-sight velocity can help us to answer these questions. I present a study of nine H II regions, with a wide variety of sizes and luminosities in the Milky Way and other Local Group galaxies. A uniform methodology of fitting a physically-motivated model structure function allows us to find the amplitude, spatial scale, and power-law slope of the velocity fluctuations in each region. Comparison with numerical experiments on synthetic datasets allows us to partially control for observational inconveniences such as finite resolution, finite map size, and projection effects. I discuss the correlations that we find between the velocity fluctuation parameters and other physical properties of 
the regions such as size and luminosity. The complex interplay between 
ordered and disordered motions can help us understand the causal 
relations between different physical processes, both within the ionized 
gas (stellar winds, photoevaporation, radiation pressure, turbulence) 
and the surrounding neutral/molecular material (gravitational collapse, 
thermal instability, magnetic fields, more turbulence).