A Chandra and ALMA Study of X-ray-irradiated Gas in the Central ~100 pc
  of the Circinus Galaxy
  We report a study of X-ray-irradiated gas in the central ~100 pc of the
Circinus galaxy, hosting a Compton-thick active galactic nucleus (AGN), at
10-pc resolution using Chandra and ALMA. Based on ~200 ksec Chandra/ACIS-S
data, we created an image of the Fe Kalpha line at 6.4 keV, tracing
X-ray-irradiated dense gas. The ALMA data in Bands 6 (~270 GHz) and 7 (~350
GHz) cover five molecular lines: CO(J=3--2), HCN(J=3--2), HCN(J=4--3),
HCO^+(J=3--2), and HCO^+(J=4--3). The detailed spatial distribution of dense
molecular gas was revealed, and compared to the iron line image. The molecular
gas emission appeared faint in regions with bright iron emission. Motivated by
this, we quantitatively discuss the possibility that the molecular gas is
efficiently dissociated by AGN X-ray irradiation (i.e., creating an
X-ray-dominated region). Based on a non-local thermodynamic equilibrium model,
we constrained the molecular gas densities and found that they are as low as
interpreted by X-ray dissociation. Furthermore, judging from inactive star
formation (SF) reported in the literature, we suggest that the X-ray emission
has potential to suppress SF, particularly in the proximity of the AGN.
