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Loïc Le Tiran’s thesis defense

Stirring Up the Gas: Star Formation and Powering High Pressures in Galaxies 10 Billion Years Ago
» Monday 5 September 2011


  • Matthew D. Lehnert (GEPI - Observatoire de Paris)

This thesis presents the analysis of a sample of 53 galaxies, observed as they were about 10 billion years ago, with the integral-field spectroscopy unit SINFONI on ESO/VLT. These galaxies have high surface brightness, more than an order of magnitude larger than those of local disks, and large ionized gas line dispersions. Gas accretion has often been suggested as a viable mechanism for driving these line dispersions. I will show that the mass accretion rate as well as the energy injection would have to be much higher than expected from simulations or from simply equating the star formation with the accretion rate to explain the high Hα surface brightness we observe in these galaxies.

I will demonstrate that star-formation plays a key role in the dynamics, ionization, and other characteristics of the warm ionized medium: the observed trend between the star-formation intensity and the velocity dispersion of the emission line gas can be modeled by a simple energy injection relationship. Also, these distant galaxies have high ISM pressures and these pressures are sufficiently high to drive vigorous outflows and strong turbulence, at least at the highest Hα surface brightness. These characteristics are similar to intense starbursts found in the nearby universe. This leads to a picture where the pressure in the ISM is determined by the intensity of the star-formation and where feedback sets the scaling between pressure and star-formation intensity. This is evidence in favor of star-formation being self-regulating, as pressure is being regulated by the star-formation and pressure likely determines the nature of star-formation. This is star-formation feedback.

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