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

Abstract

NGC~613 is a nearby barred spiral galaxy with a nuclear ring. Exploiting high spatial resolution ($\approx 20$ pc) Atacama Large Millimeter/sub-millimeter Array ${}^{12}$CO(1-0) 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 ($R_{\mathrm{c}}$) are comparable to those of the clouds in the Milky Way (MW) disc, but their gas masses, observed linewidths ($\ddot{I}{ƒ}_{\mathrm{obs},\mathrm{los}}$) and gas mass surface densities are larger. The GMC size -- linewidth relation ($\ddot{I}{ƒ}_{\mathrm{obs},\mathrm{los}}\propto R_{\mathrm{c}}^{0.77}$) 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 $⟨\hat{I}{\pm }_{\mathrm{obs},\mathrm{vir}}⟩\approx 1.7$). 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.

15 pages, 8 figures, accepted for publication in MNRAS. arXiv admin note: text overlap with arXiv:2304.10471