Infrared dark clouds on the far side of the Galaxy

摘要: Context. Infrared dark clouds are the coldest and densest portions of giant molecular clouds. The most massive ones represent some likely birthplaces for next generation stars in Milky Way. Because a strong mid-IR background is needed to make them appear absorption, they usually assumed be nearby. Aims: We use THz absorption spectroscopy solve distance ambiguity associated with kinematic distances IR-dark TOP100 ATLASGAL sample, flux-limited selection clumps different evolutionary phases star formation. Methods: para-H2O ground state transition at 1113.343 GHz, observed Herschel/HIFI, was used investigate occurrence foreground along line sight directly towards infrared-dark Additional consistency checks were performed using MALT90 HiGAL archival data targeted Mopra APEX spectroscopic observations. Results: report first discovery five IRDCs lying conclusively far distance, showing that mere presence low-contrast not sufficient unequivocally resolve near/far favour former. All actively forming high-mass stars; four also show infall signatures. Conclusions: give estimate fraction sources (~11% TOP100) describe their appearance properties. assumption all lie near may lead, cases, underestimating masses, sizes, luminosities, possibly causing missed will form very clusters. Figure 2 Appendix A available electronic http://www.aanda.org