Spatially Dependent Photometric Activity of M dwarfs in the Solar Cylinder

TL;DR

This study investigates how the magnetic activity of M dwarf stars varies with their position in the Galaxy, revealing a decline in flaring activity with age and height above the Galactic plane, with implications for stellar evolution.

Contribution

It provides the first large-scale analysis of spatial dependence of M dwarf activity using 3.6 million stars, identifying a clear relationship between Galactic location and flare activity.

Findings

Flaring fraction decreases with stellar age and height above the Galactic plane.

No significant radial gradient in flare activity within 500 pc of the Sun.

Activity saturation observed in stars within 50 pc, regardless of spectral type.

Abstract

We study the relationship between Galactic location ($R, Z$) and photometric activity for 3.6 million M dwarf stars within 1 kpc of the Sun. For this purpose, we identify 906 unique flare events as a proxy for magnetic activity from the SkyMapper Southern Survey DR3. We adopt vertical distance $|Z|$ from the Galactic disc as a proxy for age and confirm a strong trend of flaring fraction decreasing with growing stellar age. Among M dwarfs within 50 pc of the Sun, we find a flaring fraction of 1-in-1,500, independent of spectral type from M2 to M7, suggesting that these stars are all in a flare-saturated young evolutionary stage. We find a hint of a kink in the slope of the overall flare fraction near 100 pc from the plane, where a steep decline begins; this slope change is visible for mid-type M dwarfs (M3--M5), suggesting it is not an artefact of mixing spectral type. Together with SDSS H$\alpha$ emission, this trend is additional evidence that the activity fraction of M dwarfs depends on Galactic height and activity lifetime. While there is a hint of flattening of the overall activity fraction above $|Z|\approx$ 500 pc, our data do not constrain this further. Within $\sim$500 pc distance from the Sun, we find no sign of radial disk gradients in flare activity, which may only be revealed by samples covering a larger radial range.