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Astron. Astrophys. 322, 53-65 (1997)

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The rich cluster of galaxies ABCG 85

I. X-ray analysis *

V. Pislar 1, F. Durret 1, 2, D. Gerbal 1, 2, G.B. Lima Neto 1, 3, 4 and E. Slezak 5

1 Institut d'Astrophysique de Paris, CNRS, Université Pierre et Marie Curie, 98bis Bd Arago, F-75014 Paris, France
2 DAEC, Observatoire de Paris, Université Paris VII, CNRS (UA 173), F-92195 Meudon Cedex, France
3 Observatoire de Lyon, Place Charles André, F-69561 St Genis Laval Cedex, France
4 Universität Potsdam, c/o Astrophysikalisches Institut Potsdam, An der Sternwarte, 16, D-14882 Potsdam, Germany
5 Observatoire de la Côte d'Azur, B.P. 229, F-06304 Nice Cedex 4, France

Received 30 July 1996 / Accepted 24 October 1996


We present an X-ray analysis of the rich cluster ABCG 85 based on ROSAT PSPC data. By applying an improved wavelet analysis, we show that our view of this cluster is notably changed from what was previously believed (a main region and a south blob). The main emission comes from the central part of the main body of the cluster on which is superimposed that of a foreground group of galaxies. The foreground group and the main cluster are separated (if redshifts are cosmological) by [FORMULA] Mpc. The southern blob is clearly not a group: it is resolved into X-ray emitting galaxies (in particular the second more luminous galaxy of the main cluster). Several X-ray features are identified with bright galaxies. We performed a spectral analysis and derived the temperature (T), metallicity (Z) and hydrogen column density ([FORMULA]). The global quantities are: T=4 keV (in agreement with the velocity dispersion of 760 km/s) and Z=0.2 [FORMULA]. We cannot derive accurate gradients for these quantities with our data, but there is strong evidence that the temperature is lower ([FORMULA]  keV) and the metallicity much higher (Z [FORMULA] [FORMULA]) in the very centre (within about [FORMULA] kpc). We present a pixel by pixel method to model the physical properties of the X-ray gas and derive its density distribution. We apply classical methods to estimate the dynamical, gas and stellar masses, as well as the cooling time and cooling flow characteristics. At the limiting radius of the image ([FORMULA] Mpc), we find [FORMULA] [FORMULA], [FORMULA] / [FORMULA]   [FORMULA]. The stellar mass is [FORMULA] [FORMULA], giving a mass to light ratio of [FORMULA]. The cooling time is estimated for different models, leading to a cooling radius of 30-80 kpc depending on the adopted cluster age; the mass deposit rate is 20-70  [FORMULA] /yr, lower than previous determinations. These results are discussed (cooling flow paradigm in relation with high Z, 'baryonic crisis' etc.) in connection with current ideas on dynamical and evolutionary properties of clusters.

Key words: galaxies: clusters: general – clusters: individual: ABCG 85 – dark matter – X-rays: galaxies

* Based on ROSAT Archive data.

Send offprint requests to: V. Pislar, pislar@iap.fr

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998