Free Access
Issue
Astron. Astrophys. Suppl. Ser.
Volume 142, Number 3, March II 2000
Page(s) 433 - 441
DOI https://doi.org/10.1051/aas:2000161
Published online 15 March 2000
DOI: 10.1051/aas:2000161

Astron. Astrophys. Suppl. Ser. 142, 433-441

X-ray and optical observations of three clusters of galaxies:Abell 901, Abell 1437, and Abell 3570[*]

S. Schindler

Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead CH41 1LD, UK
e-mail: sas@staru1.livjm.ac.uk

Received September 1, 1999; accepted January 4, 2000

Abstract:

We analyse three clusters of galaxies, Abell 901 (z=0.17), Abell 1437 (z=0.13) and Abell 3570 (z=0.037). They have low to intermediate X-ray fluxes and an irregular morphology in the ROSAT All-Sky Survey (RASS). These clusters are chosen to test the abilities and limitations of the RASS in terms of cluster fluxes and cluster morphologies. Therefore some "worst'' cases are used here. X-ray observations with the ROSAT/HRI and optical spectroscopic observations are carried out. The ROSAT/HRI observations, which have a much better spatial resolution than the RASS, reveal in two of the three cases a significantly different morphology than seen in the RASS. The reasons are point sources which could not be resolved in the RASS and were therefore confused with the cluster emission. For A3570 we could confirm the relaxed state of the cluster by the optical determination of a small velocity dispersion. In the cluster with the lowest flux (Abell 901) the countrate measurement is strongly affected by point sources, in the two other cases the countrate measurements of the RASS are reliable, i.e. they are reproduced by the ROSAT/HRI measurement. We conclude that for clusters with a flux of a few times 10-12erg/cm2/s or smaller, which show at the same time a non-relaxed morphology, the flux measurement of the RASS can be seriously affected by fore- or background sources. We point out that an all-sky survey of a second ABRIXAS mission would provide a much clearer source distinction for low-flux clusters and thus a much improved countrate determination.

Key words: galaxies: clusters: individual: Abell 901, Abell 1437, Abell 3570 -- intergalactic medium -- cosmology: observations -- X-rays: galaxies

SIMBAD Objects

Copyright The European Southern Observatory (ESO)

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.