Piecing the physical and chemical conditions of early-stage cores: ammonia observations from GBT and VLA

Abstract: Pre-stellar cores represent a crucial phase in the evolution of low-mass star formation. Understanding the physical conditions within these pre-stellar cores is essential for comprehending the dynamic processes of star formation and related chemical reactions. While in most cases, molecular species freeze out onto grain surfaces within the cold and dense gas of these cores, nitrogen-bearing species are exceptions, and NH3, in particular, has long served as a valuable tool for probing the physical conditions within pre-stellar cores. Through high-angular-resolution observations of the NH3 (1,1) and (2,2) inversion transitions obtained with the Very Large Array (VLA) and the Green Bank Telescope (GBT), we have uncovered detailed thermal structures in three early-stage cores: the starless core L1517B, and the pre-stellar cores L694-2 and L429. By utilizing high-resolution extinction maps, we have determined gas density profiles and evaluated variations in NH3 abundance in relation to gas volume density and core evolutionary stages. Our results indicate a progressive depletion of NH3 with increasing central density within pre-stellar cores, underscoring the significance of high-resolution observations in revealing the intricate physical structure and molecular depletion processes in the innermost regions of these cores.