The Structure, Dynamics and Star Formation Rate of the Orion Nebula Cluster

Abstract

The spatial morphology and dynamical status of a young, still-forming stellar cluster provide valuable clues on the conditions during the star formation event and the processes that regulated it. We analyze the Orion Nebula Cluster (ONC), utilizing the latest censuses of its stellar content and membership estimates over a large wavelength range. We determine the center of mass of the ONC, and study the radial dependence of angular substructure. The core appears rounder and smoother than the outskirts, consistent with a higher degree of dynamical processing. At larger distances the departure from circular symmetry is mostly driven by the elongation of the system, with very little additional substructure, indicating a somewhat evolved spatial morphology or an expanding halo. We determine the mass density profile of the cluster, which is well fitted by a power law that is slightly steeper than a singular isothermal sphere. Together with the ISM density, estimated from average stellar extinction, the mass content of the ONC is insufficient by a factor $\sim 1.8$ to reproduce the observed velocity dispersion from virialized motions, in agreement with previous assessments that the ONC is moderately supervirial. This may indicate recent gas dispersal. Based on the latest estimates for the age spread in the system and our density profiles, we find that, at the half-mass radius, 90% of the stellar population formed within $\sim 5$-$8$ free-fall times ($t_{\mathrm{ff}}$). This implies a star formation efficiency per $t_{\mathrm{ff}}$ of ${\epsilon }_{\mathrm{ff}}\sim 0.04$-$0.07$, i.e., relatively slow and inefficient star formation rates during star cluster formation.

ApJ accepted; 17 pages, 13 figures

References in corpus (12)

• The distance to the Orion Nebula
• A Spitzer Survey of Young Stellar Clusters within One Kiloparsec of the Sun: Cluster Core Extraction and Basic Structural Analysis
• Slow Star Formation in Dense Gas: Evidence and Implications
• The ACS Survey of Galactic Globular Clusters. I. Overview and Clusters Without Previous HST Photometry
• Dynamical mass segregation on a very short timescale
• Equilibrium Star Cluster Formation
• On the Rapid Collapse and Evolution of Molecular Clouds
• On the Structure of the Orion A Cloud and the Formation of the Orion Nebula Cluster
• The Spatial Structure of Young Stellar Clusters. I. Subclusters
• Dynamics of Dense Cores in the Perseus Molecular Cloud
• Kinematic Structure of the Orion Nebula Cluster and its Surroundings
• Core-Halo Age Gradients and Star Formation in the Orion Nebula and NGC~2024 Young Stellar Clusters

Cited by in corpus (26)

• Expanding bubbles in Orion A: [CII] observations of M42, M43, and NGC 1977
• Numerical Simulations of Turbulent Molecular Clouds Regulated by Radiation Feedback Forces II: Radiation-Gas Interactions and Outflows
• The 3-D Kinematics of the Orion Nebula Cluster: NIRSPEC-AO Radial Velocities of the Core Population
• Hunting for Runaways from the Orion Nebula Cluster
• Mapping young stellar populations towards Orion with Gaia DR1
• The Structural Evolution of Forming and Early Stage Star Clusters
• HST survey of the Orion Nebula Cluster in the H${}_2$O 1.4 $\mu$m absorption band: II. The substellar IMF down to planetary masses
• Low Mass Stars as Tracers of Star and Cluster Formation
• [CII] $158\mu \mathrm{m}$ line emission from Orion A. I. A template for extragalactic studies?
• A gravitational and dynamical framework of star formation: The Orion Nebula
• Binary Formation in the Orion Nebula Cluster: Exploring the Sub-stellar Limit
• HST astrometry in the Orion Nebula Cluster: census of low-mass runaways
• Testing Feedback from Star Clusters in Simulations of the Milky Way Formation
• Astrochemical modelling of infrared dark clouds
• Quantifying kinematic substructure in star-forming regions with statistical tests of spatial autocorrelation
• Magnetic Fields and Galactic Star Formation Rates
• SIRIUS Project. IV. The formation history of the Orion Nebula Cluster driven by clump mergers
• Expansion Kinematics of Young Clusters. I. Lambda Ori
• Which young clusters/associations are we missing today?
• Simulated observations of star formation regions: infrared evolution of globally collapsing clouds
• The 3D Kinematics of the Orion Nebula Cluster II: Mass-dependent Kinematics of the Inner Cluster
• Report on Optimal Substructure Techniques for Stellar, Gas and Combined Samples
• Analysis of Selected Runaway Stars in the Orion Nebula Based on Data from the Gaia EDR3 Catalogue
• Theory of Turbulent Equilibrium Spheres with Power-Law Linewidth-Size Relation
• Water emission tracing active star formation from the Milky Way to high-$z$ galaxies
• Stirred, not shaken: Star cluster survival in the slingshot scenario