Fountain-driven gas accretion feeding star formation over the disc of NGC 2403

TL;DR

This study models the galactic fountain process in NGC 2403, demonstrating that accretion from the hot circumgalactic medium sustains star formation and disc growth, aligning well with observed gas dynamics and mass.

Contribution

It introduces a dynamical model linking galactic fountain activity with hot CGM condensation, explaining neutral gas accretion and star formation in NGC 2403.

Findings

Accretion rate matches star formation rate (~0.8 M_sun/yr)

Model reproduces EPG distribution and kinematics accurately

Fountain-driven condensation supports disc growth and inside-out formation

Abstract

We use a dynamical model of galactic fountain to study the neutral extraplanar gas (EPG) in the nearby spiral galaxy NGC 2403. We have modelled the EPG as a combination of material ejected from the disc by stellar feedback (i.e. galactic fountain) and gas accreting from the inner circumgalactic medium (CGM). This accretion is expected to occur because of cooling/condensation of the hot CGM (corona) triggered by the fountain. Our dynamical model reproduces the distribution and kinematics of the EPG H$\mathrm{\scriptsize{I}}$ emission in NGC 2403 remarkably well and suggests a total EPG mass of $4.7^{+1.2}_{-0.9}\times10^8\mathrm{M}_\odot$, with a typical scale height of around 1 kpc and a vertical gradient of the rotation velocity of $-10.0\pm2.7\,\mathrm{km\,s^{-1}\,kpc^{-1}}$. The best-fitting model requires a characteristic outflow velocity of $50\pm10\,\mathrm{km\,s^{-1}}$. The outflowing gas starts out mostly ionised and only becomes neutral later in the trajectory. The accretion rate from the condensation of the inner hot CGM inferred by the model is 0.8$\,\mathrm{M}_\odot\,\mathrm{yr}^{-1}$, approximately equal to the star formation rate in this galaxy (0.6$\,\mathrm{M}_\odot\,\mathrm{yr}^{-1}$). We show that the accretion profile, which peaks at a radius of about 4.5$\,$kpc, predicts a disc growth rate compatible with the observed value. Our results indicate that fountain-driven corona condensation is a likely mechanism to sustain star formation as well as the disc inside-out growth in local disc galaxies.