Height-dependent thermal properties of extreme-ultraviolet campfires in the quiet Sun

Small-scale impulsive energy-release events are widely considered a key ingredient of quiet-Sun coronal heating. We quantify the thermal energies and height dependence of EUV campfires from a single observing sequence on 30 May 2020 with Solar Orbiter/EUI HRI EUV at 174 Angstrom. Temperatures and emission measures are adopted from SDO/AIA diagnostics. We explore geometric uncertainties using multiple volume models and characterise the distributions using cumulative distribution functions and maximum-likelihood methods, with Solar Orbiter/STIX microflares and SDO/AIA nanoflare-like events as comparisons. Short-duration campfires occur at all heights, whereas longer-lived brightenings are preferentially associated with chromospheric layers. Emitting volumes and thermal energies show no comparable height dependence. Background-subtracted thermal energies span approximately 10 20-10 24 erg, with rare events reaching about 5 x 10 24 erg. The statistically robust power-law regime extends over approximately 10 22-10 24 erg. Estimates without background subtraction are systematically higher by about one order of magnitude. Directly detected campfires contribute a sub-percent fraction of the canonical quiet-Sun heating requirement. Approximately accounting for the detection threshold and DEM completeness, a more complete census could raise this to a few percent, but this remains a single-epoch, order-of-magnitude estimate. EUV campfires extend the flare energy distribution toward lower energies and provide height-resolved constraints on impulsive heating. The excess of long-lived events in the lower chromosphere, combined with broadly invariant energy and volume distributions, indicates that atmospheric stratification primarily modulates cooling and dissipation timescales rather than the characteristic energy scale of the heating process.