EPoS Contribution
EPoS Contribution
On the gravitational content of molecular clouds and their cores

Javier Ballesteros-Paredes
Centro de Radioastronomia y Astrofisica, UNAM, Morelia, Mexico
Although the gravitational term entering in the Virial theorem is usually assumed to be equal to the gravitational energy by neglecting the contribution from mass distribution outside the volume of integration, such approximation may not be valid in the presence of an important external gravitational field. In the present work I analyze the effect of an external gravitational field over a density structure. The cases under analysis are (a) an idealized giant molecular cloud (GMC) embedded within a galactic gravitational potential, and (b) an idealized molecular cloud core embedded within the gravitational potential of its (also idealized) parental molecular cloud. The results show that, for filamentary GMCs elongated on the plane of the galaxy, the shear can be a dominant source for support against gravity. This may explain the presence of some GMCs with no signs of massive star formation, as is the case of the Maddalena's cloud. For less filamentary GMCs, however, the tidal tearing in the x-y plane is compensated by a tidal compression in the z direction. Such clouds, then, have a smaller influence of the external gravitational potential on their total gravitational budget (up to ~ 15-25%). However, in the case of the dense core embedded in its parental molecular cloud, Wext becomes equal or even more important than the gravitational energy Eg, specially at the wells of the gravitational potential of the cloud. We also find that the strong contribution from Wext work in the same direction than the gravitational energy Eg, i.e., that whenever Wext is important, it favors the collapse of the structure. We speculate on the implications of these results for star formation models.