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ROSAT PSPC observations of 5 X-ray bright early type galaxies
G. Trinchieri 1, 2,
G. Fabbiano 3 and
D-W. Kim 4
Received 4 March 1996 / Accepted 1 July 1996
We report on the ROSAT PSPC observations of 5 X-ray bright early-type galaxies. Their X-ray morphology is more complex than Einstein data had shown, ranging from the ellipsoidal shape of NGC 533 to the 200 kpc tail of NGC 7619. Hot gas at an average temperature of 0.8-1 keV dominates their X-ray emission. The spectral analysis is based on the assumption of a hot thin plasma at cosmic abundances, since the spectral resolution of the PSPC does not allow unambiguous measures of the model parameters (temperatures, low energy cut-off, metal abundance). However, the estimated temperature are not strongly affected by this choice. A temperature distribution of the hot interstellar medium is also derived. Higher temperatures are in some cases observed at larger radii, while the innermost region is cooler in all of the objects studied. Due to the large range in distances however this corresponds to significantly different galaxy radii, from 5 kpc in NGC 4649 to 30 kpc in NGC 533.
The temperature and density distributions derived are used to estimate the total mass of these systems, which span from 10 and corresponding mass-to-light ratios M/L 10-150 in solar units. Formal errors on the derived masses are estimated to be 25%.
Care must be taken in comparing results for different systems, since some of the emission attributed to these objects could suffer from the contribution for the groups and clusters they belong to. Accordingly, our mass estimates could reflect the effect of the cluster/group potential.
Key words: galaxies: individual: NGC 533 galaxies: individual: NGC 2563 galaxies: individual: NGC 4649 galaxies: individual: NGC 7619 galaxies: individual: NGC 7626 X-rays: galaxies
Send offprint requests to: G. Trinchieri
Online publication: July 8, 1998