Stellar Feedback and Resolved Stellar IFU Spectroscopy in the Nearby Spiral Galaxy NGC 300

Abstract

We present MUSE Integral Field Unit (IFU) observations of five individual HII regions in two giant (> 100 pc in radius) star-forming complexes in the low-metallicity (Z ∼ 0.33 Z ) nearby (D ∼ 2 Mpc) dwarf spiral galaxy NGC 300. We combine the IFU data with high spatial resolution Hubble Space Telescope photometry to demonstrate the extraction of stellar spectra and the classification of individual stars from ground-based data at the distance of 2 Mpc. For the two star-forming complexes, in which no O-type stars had previously been identified, we find a total of 13 newly identified O-type stars in the mass range 15−50 M , as well as 4 Wolf-Rayet stars (two already known sources and two Wolf-Rayet star candidates that are now confirmed in this work). We use the derived massive stellar content to analyze the impact of stellar feedback on the HII regions. As already found for HII regions in the Magellanic Clouds, the dynamics of the analyzed NGC 300 HII regions are dominated by a combination of the pressure of the ionized gas and stellar winds. By comparing the derived ionized gas mass loading factors to the total gas mass loading factor across the NGC 300 disk, we find that the latter is an order of magnitude higher, either indicating very early evolutionary stages for these HII regions, or being a direct result of the multi-phase nature of feedback-driven bubbles. Moreover, we analyze the relation between the star formation rate and the pressure of the ionized gas as derived from small (< 100 pc) scales, as both quantities are systematically overestimated when derived on galactic scales. With the wealth of ongoing and upcoming IFU instruments and programs, this study serves as a pathfinder for the systematic investigation of resolved stellar feedback in nearby galaxies, and it delivers the necessary analysis tools to enable massive stellar content and feedback studies sampling an unprecedented range of HII region properties across entire galaxies in the nearby Universe.

Which feedback mechanisms dominate in the high-pressure environment of the central molecular zone?

“…A similar conclusion was recently reached for giant molecular clouds in NGC 300, which have a mean separation length that closely matches the gas disc scale height, suggesting that their inplane spacing is set by feedback bubbles breaking out of the disc (Kruijssen et al 2019b). Interestingly, the H ii region expansion velocities measured across the nearby galaxy population are highly similar to the ones obtained here for the Galactic Centre and have also been attributed to thermal feedback (Kruijssen et al 2019b;Chevance et al 2020c,a;McLeod et al 2020). Together with the present work, these studies provide evidence for feedback-regulated cloud lifecycles, with surprisingly universal characteristics over three orders of magnitude in ambient gas pressure.…”

“…Currently, however, H ii regions within a limited sample of sources have been investigated in a comparable manner (e.g. Lopez et al 2011Lopez et al , 2014McLeod et al 2019McLeod et al , 2020. We make use of the data taken from, Lopez et al (2011) who investigated the pressure components within the massive star-forming region 30 Doradus in the Large Magellanic Cloud, and Lopez et al (2014, data taken from their Table 7) who then expanded this study to 32 H ii regions with ages of ∼ 3 − 10 Myr within both the Small and Large Magellanic Clouds (SMC and LMC, respectively).…”

“…Lopez et al 2011Lopez et al , 2014Chevance et al 2016;McLeod et al 2019), as well as other nearby galaxies (e.g. McLeod et al 2020). These studies have provided important insights into early-stage feedback, but further work is needed to understand how preprocessing varies with environment, particularly to higher density, pressure, and metallicity regimes such as those in galactic nuclei and high-redshift galaxies.…”

The Molecular Cloud Lifecycle

“…Eventually, the energy and momentum input from newly formed star-forming regions begins to dominate and the parent cloud is dispersed by stellar feedback (e.g. Lopez et al 2014;Rahner et al 2017Rahner et al , 2019Grudić et al 2018;Haid et al 2018;Kruijssen et al 2019b;McLeod et al 2020, among many others).…”

An uncertainty principle for star formation – V. The influence of dust extinction on star formation rate tracer lifetimes and the inferred molecular cloud lifecycle

“…The maps are continuum-subtracted using R-band imaging. They also include a uniform correction for contamination by [N II] line emission, based on integral field spectroscopic observations of the same targets, assuming a contamination of 20 per cent for NGC 300 (McLeod et al 2020) and 30 per cent for the other galaxies (Kreckel et al 2019). The maps are not corrected for stellar absorption, but its effect is negligible for the young regions that we consider (Haydon et al 2018).…”