We present the first high spatial resolution X-ray study of the massive star forming region NGC 6357 , obtained in a 38 ks Chandra /ACIS observation .
Inside the brightest constituent of this large HII region complex is the massive open cluster Pismis 24 .
It contains two of the brightest and bluest stars known , yet remains poorly studied ; only a handful of optically bright stellar members have been identified .
We investigate the cluster extent and Initial Mass Function and detect \sim 800 X-ray sources with a limiting sensitivity of \sim 10 ^ { 30 } ergs s ^ { -1 } ; this provides the first reliable probe of the rich intermediate-mass and low-mass population of this massive cluster , increasing the number of known members from optical study by a factor of \sim 50 .
The high luminosity end ( \log L _ { h } [ 2-8 keV ] \geq 30.3 ergs s ^ { -1 } ) of the observed X-ray luminosity function in NGC 6357 is clearly consistent with a power law relation as seen in the Orion Nebula Cluster and Cepheus B , yielding the first estimate of NGC 6357 ’ s total cluster population , a few times the known Orion population .
We investigate the structure of the cluster , finding small-scale substructures superposed on a spherical cluster with 6 pc extent , and discuss its relationship to the nebular morphology .
The long-standing L _ { X } -10 ^ { -7 } ~ { } L _ { bol } correlation for O stars is confirmed .
Twenty-four candidate O stars and one possible new obscured massive YSO or Wolf-Rayet star are presented .
Many cluster members are estimated to be intermediate-mass stars from available infrared photometry ( assuming an age of \sim 1 Myr ) , but only a few exhibit K -band excess .
We report the first detection of X-ray emission from an Evaporating Gaseous Globule at the tip of a molecular pillar ; this source is likely a B0-B2 protostar .