Larson’s relations have been fundamental observational pieces for understanding the dynamics and structure of molecular clouds (MCs). I will make a critical revision of them, in order to understand what is the origin of each one, and what do they tell us in terms of the structure, dynamics and evolution of MCs. Thus, using numerical simulations, I will show the evolution of MCs in the Larson’s planes: the velocity dispersion-size, the virial parameter vs size and vs mass, and the mass-size plane. I will show that clouds tend to lower their sizes, and increase their column density and velocity dispersion in such a way that they tend to virialization, regardless if they started sub- or super-virial. I will discuss also the different exponents of the mass-size relation, showing: (a) why MCs exhibit a tight power-law correlation with slope of 2 when observed in extinction, and (b) why CO surveys tend to report exponents slightly larger, of the order of 2.3, with substantially more scatter. I will discuss what are the implications of these differences in terms of the structure of the Milky Way, rather than the internal structure of MCs. Finally, (c) why when observing internally a single cloud, the exponent found has to be necessarily smaller than 2, and what are the implications in terms of the actual internal structure of MCs.
Enviado por j.ballesteros@irya.unam.mx, 2019 Oct