Guillaume Pineau Des Forets

H3+ recombination and bistability in the interstellar medium

H3+ has recently been detected using infrared absorption towards several dense clouds. We have already shown that models of interstellar chemistry can exhibit several stable steady states, due to the nonlinear behaviour of chemical equations in which H3+ plays a major role. We investigate the influence of various astrophysical parameters that control the evolution and the final state of the gas, such as the density, the cosmic–ray ionization rate, the elemental depletions, and the H3+ dissociative recombination rate (which is a key reaction). We show that these parameters lead to bistability for a range of physical conditions appropriate to interstellar clouds and discuss more specifically their influence on the H3+ abundance in dark clouds. Both steady-state and evolutionary aspects are discussed.

Supernova Impact on a Molecular Cloud in the Local Bubble

We present evidence for the impact of a supernova blast‐wave on a molecular cloud located inside the Local Bubble, in the area of interaction with the Sco‐Cen OB association.The evidence comes from the analysis of the line of sight toward the nearby (170 pc) star HD102065, located behind the tail of a cometary‐shaped, infrared cirrus‐cloud which we believe is only 70 pc away from the Sun. The analysis includes numerous transitions of atoms, ions and molecules, in absorption and in emission, in the UV, the optical and the sub‐millimeter.Several peculiar characteristics of the cloud like the spatial structure of its cold phase, the high negative velocities, the high abundance of atoms in excited states and the highly ionized species associated with the highest velocities, as well as the unusually high abundance of small dust particles, are interpreted as the result of the interaction with a supernova shock wave.This line of sight provides an ideal laboratory to study turbulent flows and mixing layers in the ISM.We present evidence for the impact of a supernova blast‐wave on a molecular cloud located inside the Local Bubble, in the area of interaction with the Sco‐Cen OB association.The evidence comes from the analysis of the line of sight toward the nearby (170 pc) star HD102065, located behind the tail of a cometary‐shaped, infrared cirrus‐cloud which we believe is only 70 pc away from the Sun. The analysis includes numerous transitions of atoms, ions and molecules, in absorption and in emission, in the UV, the optical and the sub‐millimeter.Several peculiar characteristics of the cloud like the spatial structure of its cold phase, the high negative velocities, the high abundance of atoms in excited states and the highly ionized species associated with the highest velocities, as well as the unusually high abundance of small dust particles, are interpreted as the result of the interaction with a supernova shock wave.This line of sight provides an ideal laboratory to study turbulent flows and mixing layers in the...

The importance of chemical data for the study of interstellar shocks

Shock waves perturb the chemical state of the interstellar gas. We consider the effects of C-shocks on the composition of molecular clouds, for a range of values of the pre-shock gas density and magnetic induction. The time required to re-establish equilibrium in the post-shock gas depends on the initial conditions and can become very large. The significance of the two known chemical phases of dark clouds and of bistability is considered in this context.

The ALMA view of the Antennae galaxy collision: How galaxy interaction triggers the formation of super star clusters

The Antennae galaxies are a spectacular example of a burst of star formation triggered by the encounter of two galaxies, being an ideal source to understand how the dynamics of galaxy mergers drives star formation. We present archive ALMA CO(3−2) and VLT near-IR H2 spectro-imaging observations, and new ALMA CO(2−1) and dust continuum observations, at ∼50 pc resolution. Combining tracers of density and velocity structure of the gas and its energetics, we demonstrate that star formation involves a complex interplay of merger-driven gas dynamics and turbulence, and the dissipation of the gas kinetic energy. We focus on a compact, bright H2 source, associated with cold molecular gas and dust continuum emission, located where the velocity gradient in the interaction region is observed to be the largest. The characteristics of this source suggest that we are witnessing the formation, initiated by turbulent dissipation, of a cloud massive enough (∼ 4×10M ) to form a super star cluster within 1 Myr.

Survival of H2 and CO in MHD Disk Winds of Class 0, Class I and Class II Stars

We present a model of warm self–similar disk winds [1], aimed at constraining the origin of molecular jets from young stars. We computed the thermal properties, ionization structure and chemical evolution, after imposing an extended molecular network of species and reactions [2]. Here we report results for typical class 0, class I and class II stars. In particular, no H2 and CO destruction occurs for younger stars (higher accretion rates), since the temperature, the ionization fraction and the X-ray photoreaction rate are lower. In general, there is as less molecular gas remaining at the recollimation point as older is the protostar.

Survival of Molecules in MHD Disk Winds

Magnetohydrodynamical (MHD) models have been constructed and observations have been conducted thoroughly for atomic jets in the past. Observations of molecular jets implied the need of further modelling of jets that would include molecular chemistry. In this work we imposed a molecular chemical network on a self–similar steady state MHD disk wind, in order to study the origin and formation mechanisms of molecular jets. We calculated the radiation field as coming from the star and hot spots on its surface; this leads to an X-ray ionization rate, which, together with UV field induced photoreactions, raises the ionization fraction at the base of the flow. The main heating mechanism is the drag heating between charged and neutral particles, and after an initial increase of the temperature at low altitudes, it is balanced mainly by adiabatic and molecular cooling. Hence the temperature is maintained at low values, and molecules are indeed able to survive.

Shock Models Revisited

We review progress in the area of the modelling of shocks in molecular clouds. In particular, we consider what has been learnt about shock structure evolution in situations where the steady-state assumption is no longer valid. We discuss the interpretation of the observed water abundance from SWAS, Odin, and ISO. We also consider the erosion of grains in shocks as well as the effect of the presence of grains on shock structure.