Formation of elongated galaxies with low masses at high redshift

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2015 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reservedWe report the identification of elongated (triaxial or prolate) galaxies in cosmological simulations at z≃2. These are preferentially low-mass galaxies (Ms≤109.5 M⊙), residing in dark-matter (DM) haloes with strongly elongated inner parts, a common feature of high-redshift DM haloes in the ΛCDM cosmology. Feedback slows formation of stars at the centres of these halos, so that a dominant and prolate DM distribution gives rise to galaxies elongated along the DM major axis. As galaxies grow in stellar mass, stars dominate the total mass within the galaxy half-mass radius, making stars and DM rounder and more oblate. A large population of elongated galaxies produces a very asymmetric distribution of projected axis ratios, as observed in high-z galaxy surveys. This indicates that the majority of the galaxies at high redshifts are not discs or spheroids but rather galaxies with elongated morphologiesThis work was partly supported, by MINECO grant AYA2012-32295, by ISF grant 24/12, by NSF grants AST-1010033 and AST-1405962, and by the I-CORE Program of the I- CORE Program of the PBC and The ISF grant 1829/1