The Carina nebula at 6 cm.

A continuum map has been made of the Carina nebula (NGC 3372) at 5 GHz with a 4' arc beam. Comparison with lower frequency data confirms that the radio spectrum is thermal and the nebula optically thin down to 400 MHz. Hydrogen 109 oc recombination line profiles with 100 kHz resolution have been obtained at 19 positions. These are unusually wide and double-peaked in the vicinity of Car II (G 287.6-0.6), the eastern component of the central double. Comparison of radio and optical brightness distribution is complicated by pronounced obscuration. However, Car II coincides with the centre of a H emission ring some 3' arc in diameter, while Car I (G 287.4-0.6), the other central peak, coincides with the edge of a well-defined lane of absorption. Hydrogen 137 and helium 109 lines have been observed in the directions of the two central continuum peaks. The p/ line ratios agree with LTE, and this suggests that electron temperatures derived from recombination lines should be correct. These average around 7000 K and ouly approach the 10000 K optical temperatures of Faulkner and Aller (1965) near the outer boundaries of the central region of the nebula, at positions where the absorption is high and no optical data are available. The recombination line velocity profiles near Car II suggest the existence of two ionization fronts with line-of-sight velocities of + 20 km -1 with respect to the mean nebula velocity of - 20 km -1 (I.s.r.). No satisfactory dynamic model of the nebula has been determined. Key words: H U regions - radio recombination lines - electron temperature