An X-Ray View of Two Infrared Dark Clouds G034.43+00.24 and G035.39−00.33

Abstract

We present a high spatial resolution Chandra X-ray study of two infrared dark clouds (IRDCs), G034.43+00.24 and G035.39−00.33, which are expected to be in the early phases of star cluster formation. We detect 112 and 209 valid X-ray point sources toward G034.43+00.24 and G035.39−00.33, respectively. We cross-match the X-ray point sources with the Two Micron All Sky Survey (2MASS), Galactic Legacy Infrared Midplane Survey Extraordinaire (GLIMPSE), and Wide-field Infrared Survey Explorer (WISE) catalogs and find 53% and 59% of the X-ray sources in G034.43+00.24 and in G035.39−00.33 have corresponding infrared counterparts, respectively. These sources are probable members of young massive clusters in formation, and using stellar isochrones we estimate that a population of 1–2 Myr old, intermediate- to high-mass young stellar objects (YSOs) exist in both IRDCs. Two and 10 Class II counterparts to X-ray sources were identified in G034.43+00.24 and in G035.39−00.33, respectively, which are located in or near dark filaments. The X-ray luminosity function (XLF) of G035.39−00.33 implies that the total mass consists of up to ∼1700 M ⊙ of stars, using the XLF of the well-studied Orion Nebula Cluster as a calibrator. This corresponds to a star formation efficiency of at most 5%, indicating the system is still very much gas dominated and in an early stage of the star formation process. The population of G034.43+00.24 is less well determined due to the lower sensitivity of its observations.