Formation of elongated galaxies with low masses at high redshift

Abstract

We report the identification of elongated (triaxial or prolate) galaxies in cosmological simulations at $z\simeq 2$. These are preferentially low-mass galaxies ($M_s\le 10^{9.5}{M}_{\odot }$), residing in dark-matter (DM) haloes with strongly elongated inner parts, a common feature of high-redshift DM haloes in the $\Lambda$CDM 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 morphologies.

7 pages, 3 figures, accepted version. Minor changes with respect to the first version

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