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The Orion Bar: from ALMA images to new dynamic PDR models

AuthorsGoicoechea, Javier R.
Issue Date2-Sep-2019
CitationThe Physics and Chemistry of the Interstellar Medium (2019)
AbstractFar-UV photons (FUV, E < 13.6 eV) from hot massive stars regulate, or at least influence, the heating, ionization, and chemistry in many regions of the ISM. The Orion Bar, the prototypical strongly irradiated PDR, is illuminated by a FUV flux of few 104 times the mean interstellar radiation field. Because of its proximity and nearly edge-on orientation, the Bar provides an excellent template to investigate the chemical content, structure, and dynamics of an irradiated molecular cloud edge. In the last years, we have used ALMA to image a small field of the Orion Bar, where the transition from atomic to molecular gas takes place. These observations provide an unprecedented sharp view of this critical transition layer (< 1'' angular resolution or < 414 AU). The resulting images show the small-scale structure in gas density and temperature, as well as the steep chemical abundance gradients. The images suggest photo-evaporative gas flows and instabilities at the edge of the molecular cloud. These observations have triggered the development of new hydrodynamic PDR models that try to explain some of the most unexpected observational results, for example the apparent small separation between the H/H2 and C+/CO dissociation fronts and the high gas thermal pressures inferred in the molecular PDR. In this talk I will stress the dynamical and non-equilibrium nature of the interaction between UV radiation from young massive stars with their parental cloud. These questions are at the core of our understanding of stellar feedback, a collection of complicated processes that take place at many galactic scales and drive the evolution of the ISM.
DescriptionXT2019, Palais des Papes, Avignon,, France, 2-6 September 2019. -- Celebrating the first 40 years of Alexander Tielens’ contribution to Science
Appears in Collections:(CFMAC-IFF) Comunicaciones congresos
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