Influence of protostellar jets and HII regions on the formation and evolution of stellar clusters

Abstract

Context. Understanding the conditions in which stars and stellar clusters form is of great importance. In particular, the role that stellar feedback may have is still hampered by large uncertainties. Aims. We aim to investigate the role played by ionising radiation and protostellar outflows during the formation and evolution of a stellar cluster. To self-consistently take into account gas accretion, we start with clumps of tens of parsecs in size. Methods. Using an adaptive mesh refinement code, we ran magneto-hydrodynamical numerical simulations aimed at describing the collapse of massive clumps with either no stellar feedback or taking into account ionising radiation and/or protostellar jets. Results. Stellar feedback substantially modifies the protostellar cluster properties in several ways. We confirm that protostellar outflows reduce the star formation rate by a factor of a few, although the outflows do not stop accretion and, likely enough, do not modify the final cluster mass. On the other hand, once sufficiently massive stars have formed, ionising radiation efficiently expels the remaining gas and reduces the final cluster mass by a factor of several. We found that while HII radiation and jets barely change the distribution of high density gas, the latter increases the dense gas velocity dispersion again by a factor of several in a few places. As we are starting from a relatively large scale, we found that the clusters whose mass and size are, respectively, of the order of a few 1000 M⊙ and a fraction of parsec, present a significant level of rotation. Moreover, we found that the sink particles that mimic the stars themselves tend to have rotation axes aligned with the cluster’s large-scale rotation. Finally, computing the classical Q parameter used to quantify stellar cluster structure, we infer that when jets are included in the calculation, the Q values are typical of observations, while when protostellar jets are not included, the Q values tend to be significantly lower. This is due to the presence of sub-clustering that is considerably reduced by the jets. Conclusions. Both large-scale gas accretion and stellar feedback, namely HII regions and protostellar jets, appear to significantly influence the formation and evolution of stellar clusters.