Investigating galactic fountains in M101

Insights from UV emission, ionised gas, and neutral gas

¹ Observatoire de Paris, LUX, CNRS, PSL University, Sorbonne University, 75014 Paris, France
² Collège de France, 11 place Marcelin Berthelot, 75231 Paris, France

^⋆ Corresponding author: aashiya.shaji@obspm.fr

Received: 10 July 2025
Accepted: 30 September 2025

Abstract

Spiral galaxy disks are thought to exist in a quasi-stationary state, between fresh gas accretion from cosmic filaments and disk star formation, self-regulated through massive-star feedback. Our goal here is to quantify these feedback processes and probe their efficiency. While star formation can be traced at 10 Myr time-scales through Hα emission, the signature of OB stars, and at 100 Myr scale with UV emission, the gas surface density is traced by H I emission for the atomic phase. We chose to investigate feedback processes using fountain effects in M101, a nearby well-observed face-on galaxy. Face-on studies are complementary to the more frequent edge-on observations of these fountains in the literature. We use high-resolution data from THINGS for the H I emission, GALEX for UV, and SITELLE-SIGNALS for the Hα tracer. We identified 20 new H I holes, in addition to the 52 holes found in 1993. We study in more detail the nine holes satisfying strong criteria to be true fountain effects, compute their physical properties, and derive their energy balance. Only one small H I hole still contains Hα and young stars inside, while the largest hole of 2.4 kpc and the oldest age (94 Myr) is deprived of Hα and UV. For face-on disks, the possibility to study simultaneously the H I shell morphology, the stellar association, and kinematic evidence is of primordial importance. In M101, we quantified how stellar feedback is responsible for carving the observed cavities in the atomic gas disk, and how it can expel neutral gas above the disk, which is then unavailable for star formation during up to 100 Myr.