Vol. 572
In section 1. Letters

Discovery of O VII line emitting gas in elliptical galaxies

by C. Pinto, A. C. Fabian, N. Werner, P. Kosec, J. Ahoranta, J. de Plaa, J. S. Kaastra, J. S. Sanders, Y.-Y. Zhang, and A. Finoguenov A&A 572, L8


Gas should be cooling on time scales of 1Gyr in the cores of galaxy clusters groups, and massive ellipticals, and a tracer of this cooling should be emission of the OVII line, which has never been detected yet in any object. The authors searched for this line in the archives of the RGS spectrometer of XMM-Newton and have discovered O VII resonance (21.6A) and forbidden (22.1A) lines for the first time in the spectra of 6 individual objects: 2 in Virgo and 4 others that are the dominant ellipticals of their groups. The O VII luminosities reveal a cooling rate of 0.2-2 Msun/yr corresponding to the predictions. Such OVII luminosities could not be detected in cool core clusters because of being farther away and because their spectra are dominated by the emission from hotter gas.