Colliding clouds and star formation in NGC 1333

Abstract

Extensive mapping of the NGC 1333 molecular cloud in CO and (C-13)O lines is presented. The velocity structure of the cloud is discussed in relation to a proposed model for the initiation of star formation by cloud-cloud collisions. Two velocity components are observed at 6.3 and 8.3 km/s, with strong self-absorption occurring only in the 8.3-km/s component. It is shown that cloud-cloud collision provides heating and compression for the back side of the 8.3-km/s cloud and that the collision causes coalescence of the two velocity components into a single intermediate-velocity component, which is observed at 7.5 km/s. A chain of newly formed stars which illuminate and heat the NGC 1333 nebulosity is found to be associated with the postcollision gas, and the region of the collision is found to be located at the intersection of an expanding neutral-hydrogen shell and a lower-velocity neutral-hydrogen background. It is concluded that ongoing star formation in the molecular cloud is a result of the collision. The kinematics of the Per OB2 association and the H I velocity field are shown to support the model of a colliding molecular cloud.