Probing the Gas Density in our Galactic Center: Moving Mesh Simulations
  of G2
  The G2 object has recently passed its pericenter passage in our Galactic
Center. While the $Br_\gamma$ emission shows clear signs of tidal interaction,
the change in the observed luminosity is only of about a factor of 2, in
contention with all previous predictions.
  We present high resolution simulations performed with the moving mesh code,
RICH, together with simple analytical arguments that reproduce the observed
$Br_\gamma$ emission. In our model, G2 is a gas cloud that undergoes tidal
disruption in a dilute ambient medium. We find that during pericenter passage,
the efficient cooling of the cloud results in a vertical collapse, compressing
the cloud by a factor of $\sim5000$. By properly taking into account the
ionization state of the gas, we find that the cloud is UV starved and are able
to reproduce the observed $Br_\gamma$ luminosity.
  For densities larger than $\approx500\;\mathrm{cm}^{-3}$ at pericenter, the
cloud fragments, due to cooling instabilities and the emitted radiation is
inconsistent with observations. For lower densities, the cloud survives the
pericenter passage intact and its emitted radiation matches the observed
lightcurve.
  From the duration of $Br_\gamma$ emission which contains both redshifted and
blueshifted components, we show that the cloud is not spherical but rather
elongated with a size ratio of 4 at year 2001. The simulated cloud's elongation
grows as it travels towards pericenter and is consistent with observations, due
to viewing angles. The simulation is also consistent with having a spherical
shape at apocenter.
