59 research outputs found
Does the dwarf galaxy system of the Milky Way originate from Andromeda?
The Local Group is often seen to be a quiescent environment without
significant merger events. However an ancient major merger may have occurred in
the most massive galaxy. Numerical simulations have shown that tidal tails
formed during gas-rich major mergers are long-lived and could be responsible
for old stellar streams and likely induce the formation of tidal dwarf galaxies
(TDGs). Using several hydrodynamical simulations we have investigated the most
prominent tidal tail formed during the first passage, which is gas-rich and
contains old and metal poor stars. We discovered several striking coincidences
after comparing its location and motion to those of the Milky Way (MW) and of
the Magellanic Clouds (MCs). First, the tidal tail is sweeping a relatively
small volume in which the MW precisely lies. Because the geometry of the merger
is somehow fixed by the anisotropic properties of the Giant Stream (GS), we
evaluate the chance of the MW to be at such a rendez-vous with this gigantic
tidal tail to be 5 %. Second, the velocity of the tidal tail matches the LMC
proper motion, and reproduce quite well the geometrical and angular momentum
properties of the MW dwarfs, i.e. the so-called disk of satellites, better
called Vast Polar Structure (VPOS). Third, the simulation of the tidal tail
reveals one of the formed TDG with mass and location almost comparable to those
of the LMC. Our present modeling is however too limited to study the detailed
interaction of gas-rich TDGs with the potential of the MW, and a complementary
study is required to test whether the dwarf intrinsic properties can be
accounted for by our scenario. Nevertheless this study suggests a causal link
between an ancient, gas-rich major merger at the M31 location, and several
enigma in the Local Group, the GS, the VPOS, and the presence of the MCs.Comment: 17 pages accepted MNRA
Could M31 be the result of a major merger?
We investigated a scenario in which M31 could be the remnant of a gas-rich
major merger. Galaxy merger simulations, highly constrained by observations,
were run using GADGET 2 in order to reproduce M31. We succeeded in reproducing
the global shape of M31, the thin disk and the bulge, and in addition some of
the main M31 large-scale features, such as the thick disk, the 10kpc ring and
the Giant Stream. This lead to a new explanation of the Giant Stream which
could be caused by tidal tail stars that have been captured by the galaxy
potential.Comment: Proceedings for the conference "Assembling the puzzle of the Milky
Way", 2 page
Reproducing properties of MW dSphs as descendants of DM-free TDGs
The Milky Way (MW) dwarf spheroidal (dSph) satellites are known to be the
most dark-matter (DM) dominated galaxies with estimates of dark to baryonic
matter reaching even above one hundred. It comes from the assumption that
dwarfs are dynamically supported by their observed velocity dispersions.
However their spatial distributions around the MW is not at random and this
could challenge their origin, previously assumed to be residues of primordial
galaxies accreted by the MW potential. Here we show that alternatively, dSphs
could be the residue of tidal dwarf galaxies (TDGs), which would have
interacted with the Galactic hot gaseous halo and disk. TDGs are gas-rich and
have been formed in a tidal tail produced during an ancient merger event at the
M31 location, and expelled towards the MW. Our simulations show that low-mass
TDGs are fragile to an interaction with the MW disk and halo hot gas. During
the interaction, their stellar content is progressively driven out of
equilibrium and strongly expands, leading to low surface brightness feature and
mimicking high dynamical M/L ratios. Our modeling can reproduce the properties,
including the kinematics, of classical MW dwarfs within the mass range of the
Magellanic Clouds to Draco. An ancient gas-rich merger at the M31 location
could then challenge the currently assumed high content of dark matter in dwarf
galaxies. We propose a simple observational test with the coming GAIA mission,
to follow their expected stellar expansion, which should not be observed within
the current theoretical framework.Comment: 17 pages, 11 figures, accepted by the Monthly Notices of the Royal
Astronomical Society (MNRAS
The vast thin plane of M31 co-rotating dwarfs: an additional fossil signature of the M31 merger and of its considerable impact in the whole Local Group
The recent discovery by Ibata et al. (2013) of a vast thin disk of satellites
(VTDS) around M31 offers a new challenge for the understanding of the Local
Group properties. This comes in addition to the unexpected proximity of the
Magellanic Clouds (MCs) to the Milky Way (MW), and to another vast polar
structure (VPOS), which is almost perpendicular to our Galaxy disk. We find
that the VTDS plane is coinciding with several stellar, tidally-induced streams
in the outskirts of M31, and, that its velocity distribution is consistent with
that of the Giant Stream (GS). This is suggestive of a common physical
mechanism, likely linked to merger tidal interactions, knowing that a similar
argument may apply to the VPOS at the MW location. Furthermore, the VTDS is
pointing towards the MW, being almost perpendicular to the MW disk, as the VPOS
is.
We compare these properties to the modelling of M31 as an ancient, gas-rich
major merger, which has been successfully used to predict the M31 substructures
and the GS origin. We find that without fine tuning, the induced tidal tails
are lying in the VTDS plane, providing a single and common origin for many
stellar streams and for the vast stellar structures surrounding both the MW and
M31. The model also reproduces quite accurately positions and velocities of the
VTDS dSphs. Our conjecture leads to a novel interpretation of the Local Group
past history, as a gigantic tidal tail due to the M31 ancient merger is
expected to send material towards the MW, including the MCs. Such a link
between M31 and the MW is expected to be quite exceptional, though it may be in
qualitative agreement with the reported rareness of MW-MCs systems in nearby
galaxies.Comment: Accepted for publication in MNRAS, 8 pages, 3 figure
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