The Great PV Ceph Outflow: A Case Study in Outflow-Cloud Interaction

We present a set of detailed molecular line maps of the region associated with the giant Herbig-Haro flow HH 315, from the young star PV Cephei, aimed at studying the outflow-cloud interaction. Our study clearly shows that the HH 315 flow is effecting the kinematics of its surrounding medium, and has been able to redistribute considerable amounts of the surrounding medium-density (∼ 10 cm) gas in its star-forming core as well at parsec-scale distances from the source. The single-dish observations include a map of the outflow in the CO(2–1) line, with a beam size of 27, and more extended maps of the outflow region in the CO(1–0) and CO(1–0) lines, with 45 and 47 beam sizes, respectively. A companion paper to this one presents higher-resolution (IRAM 30-m) observations, and discusses their implications (Arce & Goodman 2002). The giant molecular outflow HH 315 is a highly asymmetric bipolar flow with a projected linear extent of about 2 pc. Our results indicate that the two outflow lobes are each interacting with the ambient medium in different ways. The southern (redshifted) lobe, with a mass of 1.8 M⊙, interacts with a dense ambient medium, very close to the young stellar outflow source, and its kinetic energy is comparable to both the turbulent and gravitational binding energy of its host cloud (of order 10 erg). In addition, we find evidence that the southern lobe is responsible for the creation of a cavity in the CO emission. In contrast, the northern (mainly blueshifted) outflow lobe, with a total mass of 4.8 M⊙, extends farther from PV Ceph and interacts with ambient gas much less dense than the southern lobe. There is very little CO emission north of the outflow source, and the only prominent CO emission is a shell-like structure coincident with the outer edge of the northern lobe, about 1.2 pc northwest of PV Ceph. It appears that the northern lobe of the HH 315 outflow has been able to “push” aside a substantial fraction of the gas in the area, piling it in a dense shell-like structure at its edges. In addition, we find that about 50% of the gas in the region of the northern lobe has been put in motion by the outflow, and that the northern outflow lobe is responsible for a velocity gradient in the ambient gas.