SIMBAD references

We discuss interstellar temperature determinations using the excitation equilibrium of the ²P levels of Si II and C II. We show how observations of the ²P_3/2fine-structure levels of Si II and C II (which have significantly different excitation energies, corresponding to ∼413 and 92 K, respectively) can be used to limit gas kinetic temperatures. We apply this method to the z=4.224 damped Lyα system toward the quasar PSS 1443+27. The lack of significant absorption out of the Si II ²P_3/2level and the presence of very strong C II ²P_3/2provide an upper limit to the temperature of the C II*-bearing gas in this system. Assuming a solar Si/C ratio, the observations imply a 2 σ limit T<954 K for this absorber; a supersolar Si/C ratio gives stricter limits, T<524 K. The observations suggest the presence of a cold neutral medium; such cold gas may serve as the fuel for star formation in this young galaxy.