WISDOM Project -- XXI. Giant molecular clouds in the central region of the barred spiral galaxy NGC 613: a steep size -- linewidth relation

NGC~613 is a nearby barred spiral galaxy with a nuclear ring. Exploiting high spatial resolution (20 pc) Atacama Large Millimeter/sub-millimeter Array ^12CO (2-1) observations, we study the giant molecular clouds (GMCs) in the nuclear ring and its vicinity, identifying 158 spatially- and spectrally-resolved GMCs. The GMC sizes (R₂) are comparable to those of the clouds in the Milky Way (MW) disc, but their gas masses, observed linewidths (₎₁ₒ, ₋₎ₒ) and gas mass surface densities are larger. The GMC size -- linewidth relation (₎₁ₒ, ₋₎ₒ R₂^0. 77) is steeper than that of the clouds of the MW disc and centre, and the GMCs are on average only marginally gravitationally bound (with a mean virial parameter ₎₁ₒ, ₕ₈ₑ1. 7). We discuss the possible origins of the steep size -- linewidth relation and enhanced observed linewidths of the clouds and suggest that a combination of mechanisms such as stellar feedback, gas accretion and cloud-cloud collisions, as well as the gas inflows driven by the large-scale bar, may play a role.