How Unusual is the Milky Way’s Assembly History?. (arXiv:2005.04969v1 [astro-ph.GA])

How Unusual is the Milky Way’s Assembly History?. (arXiv:2005.04969v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Evans_T/0/1/0/all/0/1">Tilly A. Evans</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fattahi_A/0/1/0/all/0/1">Azadeh Fattahi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Deason_A/0/1/0/all/0/1">Alis J. Deason</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Frenk_C/0/1/0/all/0/1">Carlos S. Frenk</a>

In the $Lambda$CDM model of structure formation galactic haloes build up by
accretion of mass and mergers of smaller subunits. The most recent massive
merger event experienced by the Milky Way (MW) halo was the accretion of the
Large Magellanic Cloud (LMC; which has a stellar mass of $sim ;
10^9M_odot$). Recent analyses of galactic stellar data from the textit{Gaia}
satellite have uncovered an earlier massive accretion event, the
Gaia-Enceladus-Sausage (GES), which merged with the MW around 10 Gyr ago. Here,
we use the EAGLE cosmological hydrodynamics simulation to study properties of
simulated MW-mass haloes constrained to have accretion histories similar to
that of the MW, specifically the recent accretion of an “LMC” galaxy and a
“GES” merger, with a quiescent period between the GES merger and the infall of
the LMC (the “GES & LMC” class). We find that $sim 16$ per cent of MW-mass
haloes have an LMC; $sim 5$ per cent have a GES event and no further merger
with an equally massive object since $z=1$; and only $0.65$ per cent belong to
the LMC & GES category. The progenitors of the MWs in this last category are
much less massive than average at early times but eventually catch up with the
mean. The LMC & GES class of galaxies naturally end up in the “blue cloud” in
the colour-magnitude diagram at $z=0$, tend to have a disc morphology and have
a larger than average number of satellite galaxies.

In the $Lambda$CDM model of structure formation galactic haloes build up by
accretion of mass and mergers of smaller subunits. The most recent massive
merger event experienced by the Milky Way (MW) halo was the accretion of the
Large Magellanic Cloud (LMC; which has a stellar mass of $sim ;
10^9M_odot$). Recent analyses of galactic stellar data from the textit{Gaia}
satellite have uncovered an earlier massive accretion event, the
Gaia-Enceladus-Sausage (GES), which merged with the MW around 10 Gyr ago. Here,
we use the EAGLE cosmological hydrodynamics simulation to study properties of
simulated MW-mass haloes constrained to have accretion histories similar to
that of the MW, specifically the recent accretion of an “LMC” galaxy and a
“GES” merger, with a quiescent period between the GES merger and the infall of
the LMC (the “GES & LMC” class). We find that $sim 16$ per cent of MW-mass
haloes have an LMC; $sim 5$ per cent have a GES event and no further merger
with an equally massive object since $z=1$; and only $0.65$ per cent belong to
the LMC & GES category. The progenitors of the MWs in this last category are
much less massive than average at early times but eventually catch up with the
mean. The LMC & GES class of galaxies naturally end up in the “blue cloud” in
the colour-magnitude diagram at $z=0$, tend to have a disc morphology and have
a larger than average number of satellite galaxies.

http://arxiv.org/icons/sfx.gif