Shaping a high-mass star-forming cluster through stellar feedback^⋆,⋆⋆

The case of the NGC 7538 IRS 1−3 complex

¹ Instituto de Ciencia de Materiales de Madrid (CSIC), Sor Juana Inés de la Cruz 3, 28049 Madrid, Spain
e-mail: pfrau@icmm.csic.es
² Observatorio Astronómico Nacional, Alfonso XII 3, 28014 Madrid, Spain
e-mail: p.frau@oan.es
³ Institut de Ciències de l’Espai, CSIC-IEEC, Campus UAB, Facultat de Ciències, Torre C5p 2, 08193 Bellaterra, Catalonia, Spain
e-mail: girart@ice.cat
⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
e-mail: qzhang@cfa.harvard.edu
⁵ Institute of Astronomy and Astrophysics, Academia Sinica, 645 N. Aohoku Place, Hilo, HI 96720, USA
e-mail: rrao@sma.hawaii.edu

Received: 31 March 2014
Accepted: 25 May 2014

Abstract

Context. NGC 7538 IRS 1−3 is a high-mass star-forming cluster with several detected dust cores, infrared sources, (ultra)compact H II regions, molecular outflows, and masers. In such a complex environment, interactions and feedback among the embedded objects are expected to play a major role in the evolution of the region.

Aims. We study the dust, kinematic, and polarimetric properties of the NGC 7538 IRS 1−3 region to investigate the role of the different forces in the formation and evolution of high-mass star-forming clusters.

Methods. We performed SMA high angular resolution observations at 880 μm with the compact configuration. We developed the RATPACKS code to generate synthetic velocity cubes from models of choice to be compared to the observational data. To quantify the stability against gravitational collapse we developed the “mass balance” analysis that accounts for all the energetics on core scales.

Results. We detect 14 dust cores from 3.5 M_⊙ to 37 M_⊙ arranged in two larger scale structures: a central bar and a filamentary spiral arm. The spiral arm presents large-scale velocity gradients in H¹³CO⁺ 4−3 and C¹⁷O 3−2, and magnetic field segments aligned well to the dust main axis. The velocity gradient is reproduced well by a spiral arm expanding at 9 km s^-1 with respect to the central core MM1, which is known to power a large precessing outflow. The energy of the outflow is comparable to the spiral-arm kinetic energy, which dominates gravitational and magnetic energies. In addition, the dynamical ages of the outflow and spiral arm are comparable. On core scales, those embedded in the central bar seem to be unstable against gravitational collapse and prone to forming high-mass stars, while those in the spiral arm have lower masses that seem to be supported by non-thermal motions and magnetic fields.

Conclusions. The NGC 7538 IRS 1−3 cluster seems to be dominated by protostellar feedback. The dusty spiral arm appears to be formed in a snowplow fashion owing to the outflow from the MM1 core. We speculate that the external pressure from the redshifted lobe of the outflow could trigger star formation in the spiral arm cores. This scenario would form a small cluster with a few central high-mass stars, surrounded by a number of low-mass stars formed through protostellar feedback.