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Probing galaxy formation with rotation curves

Le 18 janvier 2019
De 10h30 à 12h00

Lorenzo Posti (ObAS)

 

Mass and angular momentum (AM) are the two pivotal quantities defining a whole range of structural properties of galaxies, such as their morphology. While cosmology has clear predictions on how much baryons should be gravitating in each potential well, it is still unclear what determines which fraction of the available baryons is eventually accreted into the galaxies that we observe today and how much AM they have retained in this process. I will show how galaxy rotation curves can be used to accurately probe both i) how much gas could cool and form stars and ii) how much AM is present in that gas. Here global galaxy scaling relations are key: the specific angular momentum-mass relation (“Fall relation”) is a tight, single, unbroken power-law from dwarfs to massive spirals, and I will show how this inevitably indicates that the efficiency of the cooling gas at AM retention must follow closely the star-formation efficiency. I will then present detailed measurements of galaxies’ star-formation efficiencies obtained fitting the rotation curves with stars+gas+DM mass models. Contrary to simple LCDM expectations, L* galaxies are not the most efficient at forming stars; instead, the star-formation efficiency monotonically increases with galaxy mass, implying that massive spirals are so efficient at forming stars that today they are left virtually without missing baryons.

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