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Determining the full satellite population of a Milky Way-mass halo in a highly resolved cosmological hydrodynamic simulation

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(2021)cite arxiv:2105.04560Comment: submitted to MNRAS, comments welcome.

Abstract

We investigate the formation of the satellite galaxy population of a Milky Way-mass halo in a very highly resolved magneto-hydrodynamic cosmological zoom-in simulation (baryonic mass resolution $m_b =$ 800 $M_ødot$). We show that the properties of the central star-forming galaxy, such as the radial stellar surface density profile and star formation history, are: i) robust to stochastic variations associated with the so-called "Butterfly Effect"; and ii) well converged over 3.5 orders of magnitude in mass resolution. We find that there are approximately five times as many satellite galaxies at this high resolution compared to a standard ($m_b10^4-5\, M_ødot$) resolution simulation of the same system. This is primarily because 2/3rds of the high resolution satellites do not form at standard resolution. A smaller fraction (1/6th) of the satellites present at high resolution form and disrupt at standard resolution; these objects are preferentially low-mass satellites on intermediate- to low-eccentricity orbits with impact parameters $30$ kpc. As a result, the radial distribution of satellites becomes substantially more centrally concentrated at higher resolution, in better agreement with recent observations of satellites around Milky Way-mass haloes. Finally, we show that our galaxy formation model successfully forms ultra-faint galaxies and reproduces the stellar velocity dispersion, half-light radii, and $V$-band luminosities of observed Milky Way and Local Group dwarf galaxies across 7 orders of magnitude in luminosity ($10^3$-$10^10$ $L_ødot$).

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