There are known differences between the physical properties of HII and diffuse ionized gas (DIG). However, most of the studied regions in the literature are relatively bright, with log10 L(H{alpha})[erg/s]>~37. We compiled an extremely faint sample of 390 HII regions with a median H{alpha} luminosity of 34.7 in the flocculent spiral galaxy NGC 300, derived their physical properties in terms of metallicity, density, extinction, and kinematics, and performed a comparative analysis of the properties of the DIG. We used MUSE data of nine fields in NGC 300, covering a galactocentric distance of zero to ~450 arcsec (~4 projected kpc), including spiral arm and inter-arm regions. We binned the data in dendrogram leaves and extracted all strong nebular emission lines. We identified HII and DIG regions and compared their electron densities, metallicity, extinction, and kinematic properties. We also tested the effectiveness of unsupervised machine-learning algorithms in distinguishing between the HII and DIG regions. The gas density in the HII and DIG regions is close to the low-density limit in all fields. The average velocity dispersion in the DIG is higher than in the HII regions, which can be explained by the DIG being 1.8kK hotter than HII gas. The DIG manifests a lower ionization parameter than HII gas, and the DIG fractions vary between 15-77%, with strong evidence of a contribution by hot low-mass evolved stars and shocks to the DIG ionization. Most of the DIG is consistent with no extinction and an oxygen metallicity that is indistinguishable from that of the HII gas. We observe a flat metallicity profile in the central region of NGC 300, without a sign of a gradient. The differences between extremely faint HII and DIG regions follow the same trends and correlations as their much brighter cousins. Both types of objects are so heterogeneous, however, that the differences within each class are larger than the differences between the two classes.

Cone search capability for table J/A+A/668/A74/ngc300 (Extremely faint HII and diffuse ionized gas (DIG) regions from MUSE data of nine fields in NGC 300)