Young open clusters in the galactic star forming region NGC 6357

Abstract

NGC6357 is an active star forming region with very young massive open clusters (OC). These clusters contain some of the most massive stars in the Galaxy and strongly interact with nearby giant molecular clouds (GMC). We study the young stellar populations of the region and of the OC Pismis24, focusing on their relationship with the nearby GMCs. We seek evidence of triggered star formation propagating from the clusters. We used new deep JHKs photometry, along with unpublished deep IRAC/Spitzer MIR photometry, complemented with optical HST/WFPC2 high spatial resolution photometry and X-ray Chandra observations, to constrain age, initial mass function, and star formation modes in progress. We carefully examine and discuss all sources of bias (saturation, confusion, different sensitivities, extinction). NGC6357 hosts three large young stellar clusters, of which Pismis24 is the most prominent. We found that Pismis24 is a very young (~1-3 Myr) OC with a Salpeter-like IMF and a few thousand members. A comparison between optical and IR photometry indicates that the fraction of members with a NIR excess (i. e., with a circumstellar disk) is in the range 0.3-0.6, consistent with its photometrically derived age. We also find that Pismis24 is likely subdivided into a few different sub-clusters, one of which contains almost all the massive members. There are indications of current star formation triggered by these massive stars, but clear age trends could not be derived (although the fraction of stars with a NIR excess does increase towards the HII region associated with the cluster). The gas out of which Pismis24 formed must have been distributed in dense clumps within a cloud of less dense gas ~1 pc in radius. Our findings provide some new insight into how young stellar populations and massive stars emerge, and evolve in the first few Myr after birth, from a giant molecular cloud complex.

arXiv comment34 pages, 26 figures, to be published in Astronomy & Astrophysics

References in corpus (61)

• Galactic Stellar and Substellar Initial Mass Function
• The Infrared Array Camera (IRAC) for the Spitzer Space Telescope
• Correcting for the Effects of Interstellar Extinction
• Embedded Clusters in Molecular Clouds
• The Dartmouth Stellar Evolution Database
• Disk Frequencies and Lifetimes in Young Clusters
• Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way
• Toward Understanding Massive Star Formation
• WFPC2 Stellar Photometry with HSTphot
• New catalogue of optically visible open clusters and candidates
• The Wavelength Dependence of Interstellar Extinction from 1.25 to 8.0 microns Using GLIMPSE Data
• Interpreting Spectral Energy Distributions from Young Stellar Objects. I. A grid of 200,000 YSO model SEDs
• Multiple populations in globular clusters. Lessons learned from the Milky Way globular clusters
• A Spitzer Survey of Young Stellar Clusters within One Kiloparsec of the Sun: Cluster Core Extraction and Basic Structural Analysis
• Absolute Calibration of the Infrared Array Camera on the Spitzer Space Telescope
• Database of Geneva stellar evolution tracks and isochrones for UBVRIJHKLL'M, HST-WFPC2, Geneva and Washington photometric systems
• 2-D Radiative Transfer in Protostellar Envelopes: II. An Evolutionary Sequence
• Massive stars in massive clusters II: Disruption of bound clusters by photoionization
• The Pisa pre-main sequence tracks and isochrones. A database covering a wide range of Z, Y, mass, and age values
• Episodic accretion at early stages of evolution of low mass stars and brown dwarfs: a solution for the observed luminosity spread in HR diagrams?
• Intrinsically Red Sources observed by Spitzer in the Galactic Mid-Plane
• Triggered massive-star formation on the borders of Galactic HII regions. I. A search for `collect and collapse' candidates
• The Progenitor Masses of Wolf-Rayet Stars and Luminous Blue Variables Determined from Cluster Turn-offs. II. Results from 12 Galactic Clusters and OB Associations
• Triggered massive-star formation on the borders of Galactic HII regions. II. Evidence for the collect and collapse process around RCW 79
• Radiation-magnetohydrodynamic simulations of HII regions and their associated PDRs in turbulent molecular clouds
• The Spatial Structure of Young Stellar Clusters. I. Subclusters
• The evolution of massive stars and their spectra I. A non-rotating 60 Msun star from the zero-age main sequence to the pre-supernova stage
• The Gaia-ESO Survey: Kinematic structure in the Gamma Velorum Cluster
• Radiation driven implosion and triggered star formation
• A Combined Spitzer and Chandra Survey of Young Stellar Objects in the Serpens Cloud Core
• Dynamical HII Region Evolution in Turbulent Molecular Clouds
• Ionizing feedback from massive stars in massive clusters: Fake bubbles and untriggered star formation
• Detailed Numerical Simulations on the Formation of Pillars around HII-regions
• The efficiency of star formation in clustered and distributed regions
• No wide spread of stellar ages in the Orion Nebula Cluster
• The masses, and the mass discrepancy of O-type stars
• The Massive Star-forming Regions Omnibus X-ray Catalog
• Correlation between the spatial distribution of the circumstellar disks and the massive stars in the open cluster NGC 6611. Compiled catalog and cluster parameters
• Star formation and disk properties in Pismis 24
• Age Gradients in the Stellar Populations of Massive Star Forming Regions Based on a New Stellar Chronometer
• Clumps and triggered star formation in ionised molecular clouds
• Star formation in 30 Doradus
• Point Sources from a Spitzer IRAC Survey of the Galactic Center
• Progressive star formation in the young galactic super star cluster NGC 3603
• Characterizing the dynamical state of star clusters from snapshots of their spatial distributions
• Estimators for the exponent and upper limit, and goodness-of-fit tests for (truncated) power-law distributions
• Ionization--induced star formation IV: Triggering in bound clusters
• Pismis 24-1: The Stellar Upper Mass Limit Preserved
• An X-ray Census of Young Stars in the Massive Southern Star-Forming Complex NGC 6357
• Search for OB stars running away from young star clusters. II. The NGC 6357 star-forming region
• Photometric determination of the mass accretion rates of pre-main sequence stars. II. NGC346 in the Small Magellanic Cloud
• O and Na abundance patterns in open clusters of the Galactic disk
• Photometric determination of the mass accretion rate of pre-main sequence stars. IV. Recent star formation in NGC 602
• Evolution of Blister-Type HII Regions in a Magnetized Medium
• X-ray variability of PMS stars - Toward an explanation of the different X-ray properties of CTTS and WTTS
• The clustered nature of star formation. Pre--main-sequence clusters in the star-forming region NGC 602/N90 in the Small Magellanic Cloud
• The IMF and Star Formation History of the Stellar Clusters in the Vela D Cloud
• VLT/FLAMES-ARGUS observations of stellar wind--ISM cloud interactions in NGC 6357
• A multifrequency study of the active star forming complex NGC6357. I. Interstellar structures linked to the open cluster Pis24
• Probing embedded star clusters in the HII complex NGC 6357 with VVV
• Molecular clouds under the influence of massive stars in the Galactic HII region G353.2+0.9

Cited by in corpus (13)

• How can young massive clusters reach their present-day sizes?
• Dynamical evolution of stars and gas of young embedded stellar sub-clusters
• Molecular clouds in the NGC 6334 and NGC 6357 region; Evidence for a 100 pc-scale cloud-cloud collision triggering the Galactic mini-starbursts
• The stellar contents and star formation in the NGC 7538 region
• Star formation in W3 - AFGL333: Young stellar content, properties and roles of external feedback
• A relation between the radial velocity dispersion of young clusters and their age: Evidence for hardening as the formation scenario of massive close binaries
• Star formation in the filament of S254-S258 OB complex: a cluster in the process of making
• Formation of Very Young Massive Clusters and implications for globular clusters
• The young stellar content of the giant HII regions M8, G333.6-0.2, and NGC6357 with VLT/KMOS
• XUE. JWST spectroscopy of externally irradiated disks around young intermediate-mass stars
• The little-studied cluster Berkeley 90. III. Cluster parameters
• Identification and analysis of the young population in the starburst galaxy NGC 253
• A possible far-ultraviolet flux-dependent core mass function in NGC 6357