The tidal evolution of the Fornax dwarf spheroidal and its globular clusters. (arXiv:2104.00011v2 [astro-ph.GA] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Borukhovetskaya_A/0/1/0/all/0/1">Alexandra Borukhovetskaya</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Errani_R/0/1/0/all/0/1">Raphael Errani</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Navarro_J/0/1/0/all/0/1">Julio F. Navarro</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:+Santos_Santos_I/0/1/0/all/0/1">Isabel Santos-Santos</a>

The dark matter (DM) content of the Fornax dwarf spheroidal galaxy inferred
from its kinematics is substantially lower than expected from LCDM cosmological
simulations. We use N-body simulations to examine whether this may be the
result of Galactic tides. We find that, despite improved proper motions from
the Gaia mission, the pericentric distance of Fornax remains poorly
constrained, mainly because its largest velocity component is roughly
anti-parallel to the solar motion. Translating Fornax’s proper motion into a
Galactocentric velocity is thus sensitively dependent on Fornax’s assumed
distance: the observed distance uncertainty, $pm 8%$, implies pericentric
distances that vary between $r_{rm peri}sim 50$ and $r_{rm peri}sim 150$
kpc. Our simulations show that for $r_{rm peri}$ in the lower range of that
estimate, a LCDM subhalo with maximum circular velocity $V_{rm max}=40$ km
s$^{-1}$ (or virial mass $M_{200}approx 10^{10} M_odot$, as expected from
LCDM) would be tidally stripped to $V_{rm max} sim 23$ km s$^{-1}$ over $10$
Gyr. This would reduce the DM mass within the Fornax stellar half-mass radius
to about half its initial value, bringing it into agreement with observations.
Tidal stripping affects mainly Fornax’s DM halo; its stellar component is
affected little, losing less than $5%$ of its initial mass in the process. We
also explore the effect of Galactic tides on the dynamical friction decay times
of Fornax’s population of globular clusters (GC) and find little evidence for
substantial changes, compared with models run in isolation. A population of GCs
with initial orbital radii between $1$ and $2$ kpc is consistent with the
present-day spatial distribution of Fornax GCs, despite assuming a cuspy halo.
Neither the DM content nor the spatial distribution of GCs seem inconsistent
with a simple model where Fornax inhabits a tidally-stripped cuspy cold DM
halo.

The dark matter (DM) content of the Fornax dwarf spheroidal galaxy inferred
from its kinematics is substantially lower than expected from LCDM cosmological
simulations. We use N-body simulations to examine whether this may be the
result of Galactic tides. We find that, despite improved proper motions from
the Gaia mission, the pericentric distance of Fornax remains poorly
constrained, mainly because its largest velocity component is roughly
anti-parallel to the solar motion. Translating Fornax’s proper motion into a
Galactocentric velocity is thus sensitively dependent on Fornax’s assumed
distance: the observed distance uncertainty, $pm 8%$, implies pericentric
distances that vary between $r_{rm peri}sim 50$ and $r_{rm peri}sim 150$
kpc. Our simulations show that for $r_{rm peri}$ in the lower range of that
estimate, a LCDM subhalo with maximum circular velocity $V_{rm max}=40$ km
s$^{-1}$ (or virial mass $M_{200}approx 10^{10} M_odot$, as expected from
LCDM) would be tidally stripped to $V_{rm max} sim 23$ km s$^{-1}$ over $10$
Gyr. This would reduce the DM mass within the Fornax stellar half-mass radius
to about half its initial value, bringing it into agreement with observations.
Tidal stripping affects mainly Fornax’s DM halo; its stellar component is
affected little, losing less than $5%$ of its initial mass in the process. We
also explore the effect of Galactic tides on the dynamical friction decay times
of Fornax’s population of globular clusters (GC) and find little evidence for
substantial changes, compared with models run in isolation. A population of GCs
with initial orbital radii between $1$ and $2$ kpc is consistent with the
present-day spatial distribution of Fornax GCs, despite assuming a cuspy halo.
Neither the DM content nor the spatial distribution of GCs seem inconsistent
with a simple model where Fornax inhabits a tidally-stripped cuspy cold DM
halo.

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