Modelling the gas kinematics of an atypical Lyman-alpha emitting compact dwarf galaxy

Abstract

Star-forming Compact Dwarf Galaxies (CDGs) resemble the expected pristine conditions of the first galaxies in the Universe and are the best systems to test models on primordial galaxy formation and evolution. Here we report on one of such CDGs, Tololo 1214-277, which presents a broad, single peaked, highly symmetric Ly$\alpha$ emission line that had evaded theoretical interpretation so far. In this paper we reproduce for the first time these line features with two different physically motivated kinematic models: an interstellar medium composed by outflowing clumps with random motions and an homogeneous gaseous sphere undergoing solid body rotation. The multiphase model requires a clump velocity dispersion of $54.3\pm 0.6$ km s${}^{-1}$ with outflows of $54.3\pm 5.1$ km s${}^{-1}$, while the bulk rotation velocity is constrained to be $348_{-48}^{+75}$ km s${}^{-1}$. We argue that the results from the multiphase model provide a correct interpretation of the data. In that case the clump velocity dispersion implies a dynamical mass of $2\times 10^9$ M${}_{\odot }$, ten times its baryonic mass. If future kinematic maps of Tololo 1214-277 confirm the velocities suggested by the multiphase model, it would provide additional support to expect such kinematic state in primordial galaxies, opening the opportunity to use the models and methods presented in this paper to constrain the physics of star formation and feedback in the early generation of Ly-$\alpha$ emitting galaxies.

arXiv comment10 pages, 5 figures, 2 tables. Accepted for publication in MNRAS

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• Lyman-$\alpha$ photons through rotating outflows