Tidally induced spiral arm wraps encoded in phase space. (arXiv:2206.03495v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Antoja_T/0/1/0/all/0/1">T. Antoja</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ramos_P/0/1/0/all/0/1">P. Ramos</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lopez_Guitart_F/0/1/0/all/0/1">F. López-Guitart</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Anders_F/0/1/0/all/0/1">F. Anders</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bernet_M/0/1/0/all/0/1">M. Bernet</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Laporte_C/0/1/0/all/0/1">C. Laporte</a>
We aim to study the dynamics of tidally induced spiral arms in our Galaxy
disc in the context of the different encounters with Sagittarius. We build toy
models of the interaction between a host and a satellite galaxy using orbital
integrations after a tidal distant encounter. We derive analytically the shape
of the structures seen in phase space as a function of time for simple
power-law potentials. We compare these models to a more realistic N-body
simulation and to real data. As previously found, an impulsive distant tidal
approach of a satellite leads to 2-armed spiral structure, made of orbits in
between their apocentres and pericentres, thus, corresponding to regions with
negative average galactocentric radial velocity. The 2-arm pattern rotates at
an angular speed of $Omega-1/2kappa$ which depends on Galactocentric radius,
thus causing a wind-up with time. This winding produces ridges in the
$R$-$V_phi$ projection with alternating signs of $V_R$ and oscillations of
$V_R$ in the $L_Z$-$phi$ space, like those in the Gaia data. The frequency of
these kinematic features increases with time, offering a powerful means to
infer the potential and the perturbation’s onset time and azimuthal phase.
Fourier analysis allows to date the impact times of simple models and even to
date perturbations from various pericentric passages. For the MW, the Fourier
analysis indicates a superposition of two frequencies, confirming previous
studies. Assuming that both are due to impulsive distant pericentre passages,
we find perturbation times <0.4 Gyr and in the range of 0.7-1.8 Gyr. The latter
is compatible with a previous pericentre of Sagittarius and would be associated
to about 4 wraps of the spiral arms in the observed radial range. Further work
on the self-gravitating response of galactic discs and possible degeneracies
with secular processes induced by the bar is necessary. (abridged)
We aim to study the dynamics of tidally induced spiral arms in our Galaxy
disc in the context of the different encounters with Sagittarius. We build toy
models of the interaction between a host and a satellite galaxy using orbital
integrations after a tidal distant encounter. We derive analytically the shape
of the structures seen in phase space as a function of time for simple
power-law potentials. We compare these models to a more realistic N-body
simulation and to real data. As previously found, an impulsive distant tidal
approach of a satellite leads to 2-armed spiral structure, made of orbits in
between their apocentres and pericentres, thus, corresponding to regions with
negative average galactocentric radial velocity. The 2-arm pattern rotates at
an angular speed of $Omega-1/2kappa$ which depends on Galactocentric radius,
thus causing a wind-up with time. This winding produces ridges in the
$R$-$V_phi$ projection with alternating signs of $V_R$ and oscillations of
$V_R$ in the $L_Z$-$phi$ space, like those in the Gaia data. The frequency of
these kinematic features increases with time, offering a powerful means to
infer the potential and the perturbation’s onset time and azimuthal phase.
Fourier analysis allows to date the impact times of simple models and even to
date perturbations from various pericentric passages. For the MW, the Fourier
analysis indicates a superposition of two frequencies, confirming previous
studies. Assuming that both are due to impulsive distant pericentre passages,
we find perturbation times <0.4 Gyr and in the range of 0.7-1.8 Gyr. The latter
is compatible with a previous pericentre of Sagittarius and would be associated
to about 4 wraps of the spiral arms in the observed radial range. Further work
on the self-gravitating response of galactic discs and possible degeneracies
with secular processes induced by the bar is necessary. (abridged)
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