The origin of a distributed stellar population in the star-forming region W4

Abstract

Stellar kinematics provides the key to understanding the formation process and dynamical evolution of stellar systems. Here, we present a kinematic study of the massive star-forming region W4 in the Cassiopeia OB6 association using the Gaia Data Release 2 and high-resolution optical spectra. This star-forming region is composed of a core cluster (IC 1805) and a stellar population distributed over 20 pc, which is a typical structural feature found in many OB associations. According to a classical model, this structural feature can be understood in the context of the dynamical evolution of a star cluster. The core-extended structure exhibits internally different kinematic properties. Stars in the core have an almost isotropic motion, and they appear to reach virial equilibrium given their velocity dispersion (0.9 +/- 0.3 km/s) comparable to that in a virial state (~0.8 km/s). On the other hand, the distributed population shows a clear pattern of radial expansion. From the N-body simulation for the dynamical evolution of a model cluster in subvirial state, we reproduce the observed structure and kinematics of stars. This model cluster experiences collapse for the first 2 Myr. Some members begin to radially escape from the cluster after the initial collapse, eventually forming a distributed population. The internal structure and kinematics of the model cluster appear similar to those of W4. Our results support the idea that the stellar population distributed over 20 pc in W4 originate from the dynamical evolution of IC 1805.

12 pages, 4 figures, 2 tables, accepted for publication in the Astrophysical Journal

References in corpus (13)

• The mass distribution and gravitational potential of the Milky Way
• New Grids of ATLAS9 Model Atmospheres
• Dynamical mass segregation on a very short timescale
• Clustered and Triggered Star Formation in W5: Observations with Spitzer
• Mass segregation in very young open clusters -- A case study of NGC 2244 and NGC 6530
• Kinematical fingerprints of star cluster early dynamical evolution
• Runaway Young Stars in the Orion Nebula
• Dynamical evolution of star-forming regions: III. Unbound stars and predictions for Gaia
• A Gaia view of the two OB associations Cygnus OB2 and Carina OB1: The signature of their formation process
• Sejong Open Cluster Survey (SOS). III. The Young Open Cluster NGC 1893 in the H II Region W8
• X-ray and optical spectroscopy of the massive young open cluster IC1805
• Understanding formation of young, distributed low-mass stars and clusters in the W4 cloud complex
• HST astrometry in the Orion Nebula Cluster: census of low-mass runaways

Cited by in corpus (10)

• First phase space portrait of a hierarchical stellar structure in the Milky Way
• A kinematic perspective on the formation process of the stellar groups in the Rosette Nebula
• Early dynamical evolution of rotating star clusters in a tidal field
• Ongoing hierarchical massive cluster assembly: the LISCA II structure in the Perseus complex
• Early dynamics and violent relaxation of multi-mass rotating star clusters
• The kinematics of young stellar population in the W5 region of the Cassiopeia OB6 association: implication on the formation process of stellar associations
• Noble gases Neon and argon: a role for the chemical patterns of multiple populations in globular clusters?
• Right round: onset and long-term evolution of rotation in star clusters
• A Gaia view on the star formation in the Monoceros OB1 and R1 associations
• Long-term evolution of multimass rotating star clusters