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We study the kinematics of the giant H II regions NGC 5455 and NGC 5471located in the galaxy M101, using integral field observations that include theHbeta and [O III] 5007 emission lines, obtained with the Keck Cosmic WebImager. We analyse the line profiles using both single and multiple Gaussiancurves, gathering evidence for the presence of several expanding shells andmoving filaments. The line decomposition shows that a broad (sigma = 30-50km/s) underlying component is ubiquitous, extending across hundreds of pc,while a large fraction of the narrow components have subsonic line widths. Thesupersonic turbulence inferred from the global line profiles is consistent withthe velocity dispersion of the individual narrow components, i.e. the globalprofiles likely arise from the combined contribution of discrete gas clouds. Weconfirm the presence of very extended (400 - 1200 km/s) low-intensity linecomponents in three bright star-forming cores in NGC 5471, possiblyrepresenting kinematic signatures of supernova remnants. For one of these, theknown supernova remnant host NGC 5471 B, we find a significantly reduced [OIII]/Hbeta line ratio relative to the surrounding photoionized gas, due to thepresence of a radiative shock at low metallicity. We explore the systematicwidth discrepancy between H I and [O III] lines, present in both global andindividual spaxel spectra. We argue that the resolution of this long-standingproblem lies in the physics of the line-emitting gas rather than in thesmearing effects induced by the different thermal widths.

Internal kinematics of giant H II regions in M101 with the Keck Cosmic Web Imager