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.

arXiv comment12 pages, 4 figures, 2 tables, accepted for publication in the Astrophysical Journal

References in corpus (42)

• Gaia Data Release 2. Summary of the contents and survey properties
• On the variation of the Initial Mass Function
• Embedded Clusters in Molecular Clouds
• Gaia Data Release 2: The astrometric solution
• Grids of stellar models with rotation - I. Models from 0.8 to 120 Msun at solar metallicity (Z = 0.014)
• Young massive star clusters
• The mass distribution and gravitational potential of the Milky Way
• A Gaia DR2 view of the Open Cluster population in the Milky Way
• On the Formation of Massive Stars
• New Grids of ATLAS9 Model Atmospheres
• RVSAO 2.0: Digital Redshifts and Radial Velocities
• The Formation of a Bound Star Cluster: From the Orion Nebula Cluster to the Pleiades
• Kinematics in Young Star Clusters and Associations with Gaia DR2
• Evidence for a systematic offset of -80 micro-arcseconds in the Gaia DR2 parallaxes
• Dynamical mass segregation on a very short timescale
• NBODY6++GPU: Ready for the gravitational million-body problem
• A dynamical origin for early mass segregation in young star clusters
• Confirmation of the $Gaia$ DR2 parallax zero-point offset using asteroseismology and spectroscopy in the $Kepler$ field
• The early dynamical evolution of cool, clumpy star clusters
• Clustered and Triggered Star Formation in W5: Observations with Spitzer
• The properties of dynamically ejected runaway and hyper-runaway stars
• Dynamical ejections of massive stars from young star clusters under diverse initial conditions
• Mass segregation in very young open clusters -- A case study of NGC 2244 and NGC 6530
• Runaway massive stars from R136: VFTS 682 is very likely a "slow runaway"
• Star Cluster Formation in a Turbulent Molecular Cloud Self-Regulated by Photo-Ionisation Feedback
• Kinematical fingerprints of star cluster early dynamical evolution
• A Catalog of OB Associations in the spiral galaxy NGC 300
• Dynamical evolution of star forming regions - II. Basic kinematics
• The Initial Mass Function and the Surface Density Profile of NGC 6231
• The Young Stellar Population of IC1613. I. A New Catalogue of OB Associations
• Stellar Proper Motions in the Orion Nebula Cluster
• Runaway Young Stars in the Orion Nebula
• An HST study of OB associations and star clusters in M101
• Dynamical evolution of star-forming regions: III. Unbound stars and predictions for Gaia
• An Optical and Infrared Photometric Study of the Young Open Cluster IC 1805 in the Giant H II Region W4
• A Gaia view of the two OB associations Cygnus OB2 and Carina OB1: The signature of their formation process
• Kinematic evidence for feedback-driven star formation in NGC 1893
• Sejong Open Cluster Survey (SOS). III. The Young Open Cluster NGC 1893 in the H II Region W8
• The Evolution of Circumstellar Disks Surrounding Intermediate Mass Stars: IC 1805
• 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

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