Vol. 580
In section 5. Galactic structure, stellar cluster and populations

[C II] emission in galactic nuclei in the presence of X-rays

by W. D. Langer and J. L. Pineda, A&A 580, A5


It has been known for two decades that the CII emission is relatively weak in massive starbursts known as ULIRGs and that the ratio CII/FIR luminosity drops at high FIR luminosity. The authors propose an explanation in terms of destruction of C+ by the X-rays emitted from an active nucleus (AGN). The AGN fraction does indeed increase with FIR luminosity. The authors compute the ionization states of carbon as a function of X-ray flux and show that C+ is depleted to the benefit of C2+ and C3+, which can dominate the carbon abundance at very high X-ray luminosities.