The Spatial Structure of Young Stellar Clusters. I. Subclusters

Abstract

The clusters of young stars in massive star-forming regions show a wide range of sizes, morphologies, and numbers of stars. Their highly subclustered structures are revealed by the MYStIX project's sample of 31,754 young stars in nearby sites of star formation (regions at distances <3.6 kpc that contain at least one O-type star.) In 17 of the regions surveyed by MYStIX, we identify subclusters of young stars using finite mixture models -- collections of isothermal ellipsoids that model individual subclusters. Maximum likelihood estimation is used to estimate the model parameters, and the Akaike Information Criterion is used to determine the number of subclusters. This procedure often successfully finds famous subclusters, such as the BN/KL complex behind the Orion Nebula Cluster and the KW-object complex in M17. A catalog of 142 subclusters is presented, with 1 to 20 subclusters per region. The subcluster core radius distribution for this sample is peaked at 0.17 pc with a standard deviation of 0.43 dex, and subcluster core radius is negatively correlated with gas/dust absorption of the stars -- a possible age effect. Based on the morphological arrangements of subclusters, we identify four classes of spatial structure: long chains of subclusters, clumpy structures, isolated clusters with a core-halo structure, and isolated clusters well fit by a single isothermal ellipsoid.

Accepted for publication in The Astrophysical Journal; 67 pages, 9 figures, and 4 tables. Supplemental materials from the online-version of this article, including machine-readable tables and source code in R are available at the public MYStIX website (http://astro.psu.edu/mystix/)

References in corpus (75)

• MCMC using Hamiltonian dynamics
• Embedded Clusters in Molecular Clouds
• The Spitzer c2d Legacy Results: Star Formation Rates and Efficiencies; Evolution and Lifetimes
• From filamentary clouds to prestellar cores to the stellar IMF: Initial highlights from the Herschel Gould Belt survey
• GLIMPSE: I. A SIRTF Legacy Project to Map the Inner Galaxy
• Young massive star clusters
• The Formation of a Star Cluster: Predicting the Properties of Stars and Brown Dwarfs
• A Spitzer Survey of Young Stellar Clusters within One Kiloparsec of the Sun: Cluster Core Extraction and Basic Structural Analysis
• Star Formation in a Crossing Time
• Infrared Dark Clouds: precursors to star clusters
• The Spitzer Space Telescope Survey of the Orion A & B Molecular Clouds - Part I: A Census of Dusty Young Stellar Objects and a Study of their Mid-IR Variability
• Stellar, Brown Dwarf, and Multiple Star Properties from Hydrodynamical Simulations of Star Cluster Formation
• Gas expulsion and the destruction of massive young clusters
• Chandra Orion Ultradeep Project: Observations and Source Lists
• The XMM-Newton Extended Survey of the Taurus Molecular Cloud (XEST)
• Cluster-formation in the Rosette molecular cloud at the junctions of filaments
• The statistical Analysis of Star Clusters
• The Spatial Distribution of Star Formation in the Solar Neighbourhood: Do all stars form in clusters?
• X-Ray Spectroscopy of Stars
• Dynamical mass segregation on a very short timescale
• How Many Infrared Dark Clouds can form Massive Stars and Clusters?
• Using the minimum spanning tree to trace mass segregation
• Global X-ray properties of the Orion Nebula region
• Equilibrium Star Cluster Formation
• Inverse dynamical population synthesis: Constraining the initial conditions of young stellar clusters by studying their binary populations
• A dynamical origin for early mass segregation in young star clusters
• Collapse and Fragmentation in Finite Sheets
• Characterizing Precursors to Stellar Clusters with Herschel
• Kinematic Structure of the Orion Nebula Cluster and its Surroundings
• On the evolution of a star cluster and its multiple stellar systems following gas dispersal
• A Pan-Carina YSO Catalog: Intermediate-Mass Young Stellar Objects in the Carina Nebula Identified Via Mid-Infrared Excess Emission
• X-ray emission from early-type stars in the Orion Nebula Cluster
• Overview of the Massive Young Star-Forming Complex Study in Infrared and X-ray (MYStIX) Project
• Universality of young cluster sequences
• Statistics of N-Body Simulations. III. Unequal Masses
• The efficiency of star formation in clustered and distributed regions
• Surface Brightness Profiles and Structural Parameters for 10 Rich Stellar Clusters in the Small Magellanic Cloud
• A Chandra Study of the Rosette Star-Forming Complex. I. The Stellar Population and Structure of the Young Open Cluster NGC 2244
• Fractal Structure in Galactic Star Fields
• A Catalog of Chandra X-ray Sources in the Carina Nebula
• Identifying Young Stars in Massive Star-Forming Regions for the MYStIX Project
• The Massive Star-forming Regions Omnibus X-ray Catalog
• Properties of hierarchically forming star clusters
• New Tests for Disruption Mechanisms of Star Clusters: Methods and Application to the Antennae Galaxies
• Age Gradients in the Stellar Populations of Massive Star Forming Regions Based on a New Stellar Chronometer
• Orion Revisited - I. The massive cluster in front of the Orion Nebula Cluster
• The MYStIX InfraRed-Excess Source Catalog
• X-ray Star Clusters in the Carina Complex
• Characterizing the dynamical state of star clusters from snapshots of their spatial distributions
• The Integrated Diffuse X-ray Emission of the Carina Nebula Compared to Other Massive Star-forming Regions
• Deep 3.8 micron Observations of the Trapezium Cluster
• X-ray emission from young brown dwarfs in the Orion Nebula Cluster
• A FLAMINGOS Deep Near Infrared Imaging Survey of the Rosette Complex I: Identification and Distribution of the Embedded Population
• Did the infant R136 and NGC 3603 clusters undergo residual gas expulsion?
• Methods for Estimating Fluxes and Absorptions of Faint X-ray Sources
• Spatial distribution of stars and brown dwarfs in sigma Orionis
• A Chandra Observation of the Obscured Star-Forming Complex W40
• The Elephant Trunk Nebula and the Trumpler 37 cluster: Contribution of triggered star formation to the total population of an HII region
• A Chandra ACIS Study of the Young Star Cluster Trumpler 15 in Carina and Correlation with Near-infrared Sources
• New Constraints on Mass-Dependent Disruption of Star Clusters in M51
• Do all stars in the solar neighbourhood form in clusters? A cautionary note on the use of the distribution of surface densities
• Bayesian Matching for X-ray and Infrared Sources in the MYStIX Project
• Stellar Clusters in the NGC 6334 Star Forming Complex
• Protoplanetary Disk Evolution around the Triggered Star Forming Region Cepheus B
• Chandra spectroscopy of the hot star beta Crucis and the discovery of a pre-main-sequence companion
• Reconstructing the Arches I: Constraining the Initial Conditions
• A Massive Young Star-Forming Complex Study in Infrared and X-ray: Mid-Infrared Observations and Catalogs
• Formation and dissolution of leaky clusters
• The Wide-Field Near Infrared Data: Optimal Photometry in Crowded Fields
• A Massive Young Star-Forming Complex Study in Infrared and X-ray: X-ray Sources in Ten Star Forming Regions
• The Progression of Star Formation in the Rosette Molecular Cloud
• Source Contamination in X-ray Studies of Star-Forming Regions: Application to the Chandra Carina Complex Project
• Modes of clustered star formation
• Formation rates of star clusters in the hierarchical merging scenario
• Reaction of Massive Clusters to Gas Expulsion - The cluster density dependence

Cited by in corpus (116)

• Star Clusters Across Cosmic Time
• Kinematics in Young Star Clusters and Associations with Gaia DR2
• The APOGEE-2 Survey of the Orion Star Forming Complex II: Six-dimensional structure
• The Spitzer Space Telescope Survey of the Orion A and B Molecular Clouds II: the Spatial Distribution and Demographics of Dusty Young Stellar Objects
• Star clusters near and far; tracing star formation across cosmic time
• Circumstellar Disk Lifetimes In Numerous Galactic Young Stellar Clusters
• Extended stellar systems in the solar neighborhood -- V. Discovery of coronae of nearby star clusters
• A Census of Young Stars and Brown Dwarfs in IC 348 and NGC 1333
• How initial size governs core collapse in globular clusters
• A model for the formation of stellar associations and clusters from giant molecular clouds
• The formation of NGC 3603 young starburst cluster: "prompt" hierarchical assembly or monolithic starburst?
• The Structure, Dynamics and Star Formation Rate of the Orion Nebula Cluster
• Unbound Young Stellar Systems: Star Formation on the loose
• The state of globular clusters at birth II: primordial binaries
• The low-mass content of the massive young star cluster RCW 38
• The Spatial Structure of Young Stellar Clusters. II. Total Young Stellar Populations
• Star Formation In Nearby Clouds (SFiNCs): X-ray And Infrared Source Catalogs And Membership
• Cluster assembly and the origin of mass segregation in the STARFORGE simulations
• The Gaia-ESO Survey and CSI 2264: Substructures, disks, and sequential star formation in the young open cluster NGC 2264
• An initial overview of the extent and structure of recent star formation within the Serpens Molecular Cloud using Gaia Data Release 2
• Multiplicity and clustering in Taurus star forming region. II. From ultra-wide pairs to dense NESTs
• CLUMP-3D. Testing $\Lambda$CDM with galaxy cluster shapes
• What is controlling the fragmentation process in the Infrared Dark Cloud G14.225-0.506? Differet level of fragmentation in twin hubs
• The Gaia-ESO Survey: Asymmetric expansion of the Lagoon Nebula cluster NGC 6530 from GES and Gaia DR2
• The substructure and halo population of the Double Cluster $h$ and $\chi$ Persei
• A WISE Census of Young Stellar Objects in Canis Major
• The Spatial Structure of Young Stellar Clusters. III. Physical Properties and Evolutionary States
• Dynamical evolution of stars and gas of young embedded stellar sub-clusters
• Simulating radiative feedback and star cluster formation in GMCs: I. Dependence on gravitational boundedness
• Observational constraints on star cluster formation theory - I. The mass-radius relation
• How fast do young star clusters expel their natal gas?: Estimating the upper limit of the gas expulsion time-scale
• A High-Resolution Multiband Survey of Westerlund 2 With the Hubble Space Telescope I: Is the Massive Star Cluster Double?
• Gaia Stellar Kinematics in the Head of the Orion A Cloud: Runaway Stellar Groups and Gravitational Infall
• Mass segregation and sequential star formation in NGC 2264 revealed by Herschel
• No evidence for protoplanetary disk destruction by OB stars in the MYStIX sample
• Intracluster Age Gradients In Numerous Young Stellar Clusters
• Classical T Tauri stars with VPHAS$+$: I: H$\alpha$ and $u$-band accretion rates in the Lagoon Nebula M8
• A probabilistic approach to emission-line galaxy classification
• Looking deep into the Rosette Nebula's heart: the (sub)stellar content of the massive young cluster NGC 2244
• Dynamical evolution of fractal structures in star-forming regions
• Tidal tails of open star clusters as probes to early gas expulsion I: A semi-analytic model
• The Gaia-ESO Survey: age spread in the star forming region NGC6530 from the HR diagram and gravity indicators
• Do the majority of stars form as gravitationally unbound?
• Runaway Young Stars in the Orion Nebula
• The low-mass population in the young cluster Stock 8: Stellar properties and Initial Mass Function
• The VMC Survey. XXIX. Turbulence-Controlled Hierarchical Star Formation in the Small Magellanic Cloud
• The 3-D Kinematics of the Orion Nebula Cluster: NIRSPEC-AO Radial Velocities of the Core Population
• The Spatial Evolution of Young Massive Clusters I. A New Tool to Quantitatively Trace Stellar Clustering
• Young Star Clusters In Nearby Molecular Clouds
• External photoevaporation of protoplanetary discs: does location matter?
• Structural studies of eight bright rimmed clouds in the southern hemisphere
• Young and embedded clusters in Cygnus-X: evidence for building up the IMF?
• A Dynamical Model for Clustered Star Formation in the Galactic Disk
• The JCMT Gould Belt Survey: Dense Core Clusters in Orion B
• Stellar cores in the Sh 2-305 H II region
• Membership lists for 431 open clusters in Gaia DR2 using extreme deconvolution gaussian mixture models
• The Role of "Black Hole Burning" in the Evolution of Dense Star Clusters
• The evolutionary tracks of young massive star clusters
• Tidal tails of open star clusters as probes to early gas expulsion II: Predictions for Gaia
• The Structural Evolution of Forming and Early Stage Star Clusters
• A High-Resolution Multiband Survey of Westerlund 2 With the Hubble Space Telescope. III. The present-day stellar mass function
• Formation of stellar clusters
• Stellar population of the Rosette Nebula and NGC 2244: application of the probabilistic random forest
• Early-Forming Massive Stars Suppress Star Formation and Hierarchical Cluster Assembly
• Early Evolution and 3D Structure of Embedded Star Clusters
• Formation of Very Young Massive Clusters and implications for globular clusters
• A tale of two clusters: dynamical history determines disc survival in Tr14 and Tr16 in the Carina Nebula
• Low Mass Stars as Tracers of Star and Cluster Formation
• The Spatial Evolution of Young Massive Clusters II. Looking for Imprints of Star Formation in NGC 2264 with Gaia DR2
• A wide-area photometric and astrometric (Gaia DR2) study of the young cluster NGC 6530
• Young open clusters in the galactic star forming region NGC 6357
• The Herschel/PACS view of the Cep OB2 region: Global protoplanetary disk evolution and clumpy star formation
• The Structure of the Young Star Cluster NGC 6231. II. Structure, Formation, and Fate
• The Dynamics, Structure, and Fate of a Young Cluster During Gas Dispersal: Hectoschelle, Chandra, Spitzer, and Gaia Observations of CepOB3b
• A gravitational and dynamical framework of star formation: The Orion Nebula
• Decoding the Morphological Evolution of Open Clusters
• The Gaia-ESO Survey: N-body modelling of the Gamma Velorum cluster
• Candidate X-ray-Emitting OB Stars in the MYStIX Massive Star-Forming Regions
• The Structure of the Young Star Cluster NGC 6231. I. Stellar Population
• Early dynamics and violent relaxation of multi-mass rotating star clusters
• The Duration of Star Formation in Galactic Giant Molecular Clouds. I. The Great Nebula in Carina
• IRAM and Gaia views of multi-episodic star formation in IC1396A: The origin and dynamics of the Class 0 protostar at the edge of an HII region
• S2D2: Small-scale Significant substructure DBSCAN Detection I. NESTs detection in 2D star-forming regions
• On the dynamical evolution of Cepheids in star clusters
• The Formation of Binary Star Clusters in the Milky Way and Large Magellanic Cloud
• Expansion Kinematics of Young Clusters. I. Lambda Ori
• Star formation in IC1396: Kinematics and subcluster structure revealed by Gaia
• Young Stellar Populations in MYStIX Star Forming Regions: Candidate Protostars
• Spectroscopic Confirmation of a Population of Isolated, Intermediate-Mass YSOs
• The evolution of phase space densities in star-forming regions
• Evolution of spatio-kinematic structures in star-forming regions: are Friends of Friends worth knowing?
• NGC 2548: clumpy spatial and kinematic structure in an intermediate-age galactic cluster
• The Effect of Molecular Cloud Properties on the Kinematics of Stars Formed in the Trifid Region
• Hierarchical Structure of YSO Clusters in the W40 and Serpens South Region: Group Extraction and Comparison with Fractal Clusters
• The NEMESIS Catalogue of Young Stellar Objects for the Orion Star Formation Complex. I. General description of data curation
• IRAS 09002-4732: A Laboratory for the Formation of Rich Stellar Clusters
• ALMAGAL VI. The spatial distribution of dense cores during the evolution of cluster-forming massive clump
• Kinematics of Subclusters in Star Cluster Complexes: Imprint of their Parental Molecular Clouds
• Report on Optimal Substructure Techniques for Stellar, Gas and Combined Samples
• Multiwavelength Studies of Young OB Associations
• Open superclusters I: The most populated primordial groups of open clusters in the third quadrant of the Galactic disc
• Mean-field theory of Bayesian clustering
• The Spatial Evolution of Young Massive Clusters III. Effect of the Gaia Filter on 2D Spatial Distribution Studies
• The kinematics of young stellar population in the W5 region of the Cassiopeia OB6 association: implication on the formation process of stellar associations
• The bound origin of low-mass stellar binaries
• Spatial distribution and clustering properties of the young stellar populations in the Carina Nebula complex and Car OB1
• A Low-speed Intruder Star in Hyades: A Temporary Residence
• Fractality of open clusters in singles, pairs, and groups
• Long-term evolution of multimass rotating star clusters
• S2D2: Small-scale Significant substructure DBSCAN Detection II. Tracing episodes and gradients of star formation activity
• Assessing membership projection errors in star forming regions
• Twinkle Twinkle Little Star, Roman Sees Where You Are: Predicting Exoplanet Transit Yields in the Rosette Nebula with the Nancy Grace Roman Space Telescope
• The Great Planetary Heist: Theft and capture in star-forming regions
• A Gaia view on the star formation in the Monoceros OB1 and R1 associations
• DarkMix: Mixture Models for the Detection and Characterization of Dark Matter Halos
• Internal dynamics and structure of Cepheus OB4. The asymmetric expansion of Berkeley 59