Molecular absorptions in high-z objects

Molecular absorption lines measured along the line of sight of distant quasars are important probes of the gas evolution in galaxies as a function of redshift. A review is made of the handful of molecular absorbing systems studied so far, with the present sensitivity of mm instruments. They produce information on the chemistry of the ISM at z \sim 1, the physical state of the gas, in terms of clumpiness, density and temperature. The CMB temperature can be derived as a function of z, and also any possible variations of fundamental constants can be constrained. With the sensitivity of ALMA, many more absorbing systems can be studied, for which some predictions and perspectives are described.Comment: 8 pages, 3 figures, in "Science with ALMA: a new era for Astrophysics", ApSS, Springer (Madrid, 13-17 November 2006

Bulge formation in disk galaxies with MOND

The formation of galaxies and their various components can be stringent tests of dark matter models and of gravity theories. In the standard cold dark matter (CDM) model, spheroids are formed through mergers in a strongly hierarchical scenario, and also in the early universe through dynamical friction in clumpy galaxies. More secularly, pseudo-bulges are formed by the inner vertical resonance with bars. The high efficiency of bulge formation is in tension with observations in the local universe of a large amount of bulge-less spiral galaxies. In the present work, the formation of bulges in very gas-rich galaxies, as those in the early universe, is studied in the Milgrom's MOdified Newtonian Dynamics (MOND), through multi-grid simulations of the non-linear gravity, including the gas dissipation, star formation and feedback. Clumpy disks are rapidly formed, as in their Newtonian equivalent systems. However, the dynamical friction is not as efficient, in the absence of dark matter halos, and the clumps have no time to coalesce into the center to form bulges, before they are eroded by stellar feedback and shear forces. Previous work has established that mergers are less frequent in MOND, and classical bulges are expected less massive. It is now shown that gas-rich clumpy galaxies in the early universe do not form bulges. Since pseudo-bulges are formed with a similar rate as in the Newtonian equivalent systems, it can be expected that the contribution of pseudo-bulges is significantly higher in MOND.Comment: 8 pages, 11 figures, accepted in Astronomy and Astrophysic

Dynamical triggering of starbursts

Galaxy interactions/mergers, gravitational instabilities and density waves, such as bars, are frequently invoked to trigger starbursts. These mechanisms have been explored through numerical simulations, with the help of various star formation recipes. Gravitational instabilities are necessary to initiate star formation, but the main trigger might be the gas flows, to provide sufficient fuel in a short time-scale. Gas accretion is also acting on the dynamics, in favoring bars/spirals, which will drive the gas inwards. Large amounts of external gas accretion are required to explain the bar frequency, and this accretion rate can be provided by the cosmic filaments, as supported by cosmological simulations. Subsequent interactions can then trigger starbursts by driving this accreted gas inwards.Comment: 6 pages, 2 figures, to appear in "The Evolution of Starbursts", ed. S. Huettemeister et al., AIP Proceeding

Astrophysical Fractals: Interstellar Medium and Galaxies

The interstellar medium is structured as a hierachy of gas clouds, that looks self-similar over 6 orders of magnitude in scales and 9 in masses. This is one of the more extended fractal in the Universe. At even larger scales, the ensemble of galaxies looks also self-similar over a certain ranges of scales, but more limited, may be over 3-4 orders of magnitude in scales. These two fractals appear to be characterized by similar Hausdorff dimensions, between 1.6 and 2. The various interpretations of these structures are discussed, in particular formation theories based on turbulence and self-gravity. In the latter, the fractal ensembles are considered in a critical state, as in second order phase transitions, when large density fluctuations are observed, that also obey scaling laws, and look self-similar over an extended range.Comment: 30 pages, 6 figures, Proceedings of "The Chaotic Universe", Roma colloquium, 1-5 Feb 99, World Scientific Advanced Series in Astrophysics and Cosmology, ed. V. Gurzadyan, Li-Zhi Fang and Remo Ruffin