Denis Puy

Molecular fluorine chemistry in the early Universe

Some models of Big Bang nucleosynthesis suggest that very high baryon density regions were formed in the early Universe, and generated the production of heavy elements other than lithium such as fluorine F. We present a comprehensive chemistry of fluorine in the post-recombination epoch. Calculation of F, F- and HF abundances, as a function of redshift z, are carried out. The main result is that the chemical conditions in the early Universe can lead to the formation of HF. The final abundance of the diatomic molecule HF is predicted to be close to 3.75 10(-17) when the initial abundance of neutral fluorine F is 10(-15). These results indicate that molecules of fluorine HF were already present during the dark age. This could have implications on the evolution of proto-objects and on the anisotropies of cosmic microwave background radiation. Hydride of fluorine HF may affect enhancement of the emission line intensity from the proto-objects and could produce spectral-spatial fluctuations.

Possible flakes of molecular hydrogen in the early Universe

The thermochemistry of H 2 and HD in non-collapsed, non-reionized primordial gas up to the end of the dark age is investigated with recent radiation-matter and chemical reaction rates taking into account the efficient coolant HD, and the possibility of a gas-solid phase transition of H 2 . In the standard big-bang model we find that these molecules can freeze out and lead to the growth of flakes of solid molecular hydrogen at redshifts z 6-12 in the unperturbed medium and under-dense regions. While this freezing caused by the mere adiabatic cooling of the expanding matter is less likely to occur in collapsed regions due to their higher than radiation background temperature, on the other hand the super-adiabatic expansion in voids strongly favors it. Later reionization (at z 5-6) eventually destroys all these H 2 flakes. The possible occurrence of H 2 flakes is important for the degree of coupling between matter and radiation, as well as for the existence of a gas-grain chemistry at the end of the dark age.

Primordial LiH: the chemistry in a collapsing protocloud

Abstract We analyse and discuss the evolution of primordial molecules during the beginning stage of the early cloud formation using an updated primordial lithium chemistry. As Puy & Signore (1996)[A&A, 305, 371], (1997)[NewA, 2, 299], we consider a simple model of a collapsing protocloud after the recombination epoch but paying special attention to the LiH formation by radiative association from excited Li atoms. Because the rate of LiH destruction through collisions with H atoms is only estimated we find that, at present, the percentage of primordial lithium converted to LiH is quite uncertain.

Cooling balance and thermal instability of a collapsing molecular protocloud

Abstract Molecular line emissions play an important role in the thermal balance of collapsing molecular clouds. In the present paper we calculate analytically the molecular cooling due to H 2 and HD, the last being the main cooling agent around 200 K (Puy & Signore, 1997 [NewA, 2, 299]). Our analysis is done under the hypothesis: we consider only the first two excited levels of the H 2 and HD molecules. We analyse the ratio between the molecular cooling due to HD and that due to H 2 . The potentiality of fragmentation of these collapsing protoclouds through the thermal instability is also discussed . Finally, we suggest that this study could also be extended to the CO molecule, because the carbon reservoir molecule CO has already been observed in high redshift objects.

From nuclei to atoms and molecules: the chemical history of the early Universe

Abstract The dark age of the Universe is generally pointed out as the period between the recombination epoch (z∼1000) and the horizon of current observations (z∼5–6). The arrow of time in the cosmic history describes the progression from simplicity to complexity, because the present Universe is clumpy and complicated unlike the homogeneous early Universe. Thus it is crucial to know the nature of the constituents, in order to understand the conditions of the formation of the first bound objects. In this paper we analyse the chemical history of this dark age through the creation of the primordial nuclei to the formation of the first atoms and molecules. Then we will describe the consequences of the molecular formation on the birth of the proto-objects. In this context we will mention the important works of Dennis W. Sciama who influenced a large number of theorists—cosmologists and astronomers—on this new field of research dedicated to primordial molecules.

The influence of magnetic fields on the Sunyaev–Zel’dovich effect in clusters of galaxies

Abstract We study the influence of intracluster large scale magnetic fields on the thermal Sunyaev–Zel’dovich (SZ) effect. In a macroscopic approach we complete the hydrostatic equilibrium equation with the magnetic field pressure component. Comparing the resulting mass distribution with a standard one, we derive a new electron density profile. For a spherically symmetric cluster model, this new profile can be written as the product of a standard (β-) profile and a radius dependent function, close to unity, which takes into account the magnetic field strength. For non-cooling flow clusters we find that the observed magnetic field values can reduce the SZ signal by ∼10% with respect to the value estimated from X-ray observations and the β-model. If a cluster harbours a cooling flow, magnetic fields tend to weaken the cooling flow influence on the SZ-effect.

Supernovae and Cosmology

Abstract These lecture notes intend to form a short pedagogical introduction to the use of typical type Ia-Supernovae (hereafter SNIa) as standard candles to determine the energy density of the universe. Problems of principle for taking SNIa as cosmological probes are pointed out, and new attempts at solving them are indicated including the empirical width–luminosity relation (WLR) and its possible explanations. Finally, the observations of SNIa at high redshift carried out by two major teams are briefly reviewed and their interpretation as evidence for an accelerating universe is also rapidly discussed

Primordial molecules at millimeter wavelengths

Chemistry plays a particular role in astrophysics. After atomic hydrogen, helium and their ions, the Universe probably contains more mass in molecules than in any other species. Molecule formation in the early, pre-galactic Universe may have had much to do with the formation of galaxies themselves. In this context the possible interaction between primordial molecules and photons of the Cosmic Microwave Background (CMB) is very important through the theoretical perspectives and constraints which could give some information on the theory of the large scale structure formation. In this paper we recall the more recent progresses on the chemistry of the early Universe, and describe the importance of molecules in the formation phase of proto objects. A special attention is done concerning the case of LiH.

COOLING FLOW BULK MOTION CORRECTIONS TO THE SUNYAEV-ZEL'DOVICH EFFECT

Abstract We study the influence of converging cooling flow bulk motions on the Sunyaev–Zel’dovich (SZ) effect. To that purpose we derive a modified Kompaneets equation which takes into account the contribution of the accelerated electron media of the cooling flow inside the cluster frame. The additional term is different from the usual kinematic SZ-effect, which depends linearly on the velocity, whereas the contribution described here is quadratic in the macroscopic electron fluid velocity, as measured in the cluster frame. For clusters with a large cooling flow mass deposition rate and/or a small central electron density, it turns out that this effect becomes relevant.

COSMOCHEMISTRY IN THE EARLY UNIVERSE

At early times the Universe was filled up with an extremely-dense and hot gas. Due to the expansion it cooled below the binding energies of atoms which led to the formation of the first nuclei. In the physical environment of the post-recombination period of hydrogen, molecules such as H 2, HD and LiH can be formed. The proto-object formation, resulting from the growth of linear density fluctuations in the early Universe, can have an important impact on the chemical state of the Universe. Hence it can be enriched with metals, and thus lead to the formation of the first pre-biotic molecules.