Probing 3D Density and Velocity Fields of ISM in Centers of Galaxies
  with Future X-Ray Observations
  Observations of bright and variable "reflected" X-ray emission from molecular
clouds located within inner hundred parsec of our Galaxy have demonstrated that
the central supermassive black hole, Sgr A*, experienced short and powerful
flares in the past few hundred years. These flares offer a truly unique
opportunity to determine 3D location of the illuminated clouds (with ~10 pc
accuracy) and to reveal their internal structure (down to 0.1 pc scales). Short
duration of the flare(s), combined with X-rays high penetration power and
insensitivity of the reflection signal to thermo- and chemo-dynamical state of
the gas, ensures that the provided diagnostics of the density and velocity
fields is unbiased and almost free of the projection and opacity effects. Sharp
and sensitive snapshots of molecular gas accessible with aid of future X-ray
observatories featuring large collecting area and high angular (arcsec-level)
and spectral (eV-level) resolution cryogenic bolometers will present invaluable
information on properties of the supersonic turbulence inside the illuminated
clouds, map their shear velocity field and allow cross-matching between X-ray
data and velocity-resolved emission of various molecular species provided by
ALMA and other ground-based facilities. This will highlight large and
small-scale dynamics of the dense gas and help uncovering specifics of the ISM
lifecycle and high-mass star formation under very extreme conditions of
galactic centers. While the former is of particular importance for the SMBH
feeding and triggering AGN feedback, the latter might be an excellent test case
for star formation taking place in high-redshift galaxies.
