Evolution of Stellar Feedback in H ii Regions

Abstract

Stellar feedback is needed to produce realistic giant molecular clouds and galaxies in simulations, but due to limited numerical resolution, feedback must be implemented using sub-grid models. Observational work is an important means to test and anchor these models, but limited studies have assessed the relative dynamical role of multiple feedback modes, particularly at the earliest stages of expansion when H II regions are still deeply embedded. In this paper, we use multiwavelength (radio, infrared, and X-ray) data to measure the pressures associated with direct radiation (P dir ), dust-processed radiation (P IR ), photoionization heating (P H II ), and shockheating from stellar winds (P X ) in a sample of 106 young, resolved H II regions with radii 0.5 pc to determine how stellar feedback drives their expansion. We find that the P IR dominates in 84% of the regions and that the median P dir and P H II are smaller than the median P IR by factors of ≈6 and ≈9, respectively. Based on the radial dependences of the pressure terms, we show that H II regions transition from P IR -dominated to P H II -dominated at radii of ∼3 pc. We find a median trapping factor of f trap ∼ 8 without any radial dependence for the sample, suggesting this value can be adopted in sub-grid feedback models. Moreover, we show that the total pressure is greater than the gravitational pressure in the majority of our sample, indicating that the feedback is sufficient to expel gas from the regions.

The impact of pre-supernova feedback and its dependence on environment

“…For example, the star formation rate (a relative increase of which over a given period of time would result in overall increased stellar feedback) is observed to be approximately constant in the portion of the galaxy covered by our observations (out to about 0.45𝑅 25 ; Gogarten et al 2010;Williams et al 2013;Casasola et al 2017), and we therefore do not consider it to be a dominant source driving the increase of stellar feedback here. In terms of evolutionary stage, one would expect the radiation pressure to be enhanced in younger, more compact regions when compared to more evolved regions (Olivier et al 2021). With a radius cutoff of about 7 pc as described we are not able to probe compact and ultra-compact H II regions, and an evolutionary dependence as traced by the ages of the stellar populations within the regions will be explored in a forthcoming paper.…”

“…With the picture emerging from the previous section in which lowermetallicity H II regions tend to have harder radiation fields, we now ask the question of whether this has measurable consequences on the impact of stellar feedback in these regions. To assess stellar feedback from the optical IFU data, we proceed as in M20 in computing feedback-related pressure terms (see also Lopez et al 2014 andOlivier et al 2021). Specifically, we focus here on the pressure of the ionised gas, 𝑃 H II , and the direct radiation pressure, 𝑃 dir , but do not quantify the effect of stellar winds.…”

“…While the impact of feedback on the environment is an established area of active research, the impact of the environment on feedback is now starting to be explored from the observational perspective (e.g. Lopez et al 2011Lopez et al , 2014Chevance et al 2016; Barnes et al 2020;Olivier et al 2021). Outstanding questions include: What are the dominant feedback mechanisms from massive stars as a function of their stellar properties (e.g.…”

Comparing the pre-SNe feedback and environmental pressures for 6000 H iiregions across 19 nearby spiral galaxies

“…More recently, many works have focused on observationally quantifying the impact of the various feedback mechanisms on driving the expansion of feedbackdriven bubbles by detailed studies of their feedback mechanisms, ionization structures, morphologies, dynamics and the stellar content across the Milky Way (e.g. Rugel et al 2019;Watkins et al 2019; Barnes et al 2020;Olivier et al 2021), the Small and Large Magellanic Clouds (Oey 1996a,b;Lopez et al 2011Lopez et al , 2014Pelle-grini et al 2010Pelle-grini et al , 2012Chevance et al 2016;McLeod et al 2019), and in nearby galaxies (e.g. McLeod et al 2020McLeod et al , 2021.…”

“…By contrasting the internal and external properties of the H II region, we will investigate different dependencies on initial and current environmental conditions. To do so, we first determine the components of the internal pressure within an H II region (see also Lopez et al 2011Lopez et al , 2014Pellegrini et al 2011;McLeod et al 2019;Barnes et al 2020;Olivier et al 2021).…”