Revelando el Agotamiento del NH3 en los Nucleos Preestelares.

Abstract

Molecular clouds are regions in the interstellar medium where molecular H2 lies and accumulates. When the concentration of molecular hydrogen becomes high enough, the properties of the region that contains it begin to change, preparing it for the collapse that, with enough evolution, will form new stars. These high-density regions are normally known as Cores, receiving a name depending on their state of evolution, starting from starless cores where there is a clear over-density but no gravitational bonding, to pre-stellar cores, where gravity plays an important role in the core dynamics. Pre-stellar cores have been extensively studied and recognized for having very special chemical traits that are expected to determine the future of the stars that will be born from them. In these terms, one specific and important property of pre-stellar cores is the high level of depletion of heavy species into dust grain surfaces. Ammonia (NH3) had been flying under the radar for more than a decade because, as observed in some observational projects, it does not freeze out as hard or at all as C and Obased molecules. In this work, we study the creation and evolution of NH3, its deuterated isotopologues, and spin isomers, making use of up-to-date chemical post-processing over the results of a state-of-art 3D hydrodynamic numerical simulation. We used this chemical post-processing scheme to see how changing some parameters affects the behavior of NH3 on an evolving slow collapse pre-stellar core and compared the results to observations. We find that a high value of CRIR, even if that is quite difficult under pre-stellar core conditions, can increase NH3 abundance and decrease the effects of freeze-out over it, while smaller grain sizes and high ortho-para ratios promote depletion heavily. We also explore the effects of implementing a density dependence for gas and dust temperatures and CRIR, which showed slight improvements from the worst isothermal cases; in particular, in the densitydependent CRIR case, we got results close to the best regular cases. We then compare our findings, mostly qualitatively, with a couple of more up-to-date observational works than our reference one, probing that our post-processing scheme, both in isothermal and densitydependent cases, can roughly recover the observed column densities on these publications, which validates our approach. We conclude that most of the parameters we have explored have a relatively weak role when we talk about regulating ammonia depletion, but there are some exceptions, as is the case when CRIR is high. Also, we find that our fiducial run does not have the best agreement with the reference case as we expected when contrasting them all, but its abundance profile is congruent with the observations over the whole evolutionary process.