Issue |
A&A
Volume 428, Number 3, December IV 2004
|
|
---|---|---|
Page(s) | 867 - 875 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20041426 | |
Published online | 07 December 2004 |
RX J1821.6+6827: A cool cluster at z = 0.81 from the ROSAT NEP survey *
1
Istituto di Radioastronomia CNR, via P. Gobetti 101, 40129 Bologna, Italy e-mail: gioia@ira.cnr.it
2
INAF – Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy e-mail: anna@brera.mi.astro.it
3
European Southern Observatory, Karl-Schwarzschild-Str. 2, Garching bei München 85740, Germany e-mail: cmullis@eso.org
4
Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822, USA e-mail: henry@ifa.hawaii.edu
5
Max-Planck-Institut fur Extraterrestrische Physik, Giessenbachstrasse, Postfach 1312, Garching 85741, Germany e-mail: hxb@xray.mpe.mpg.de,ugb@xray.mpe.mpg.de
Received:
7
June
2004
Accepted:
30
July
2004
We present an analysis of the properties of the cluster of galaxies
RX J1821.6+6827, or NEP 5281, at a redshift .
RX J1821.6+6827 was discovered during the optical identification
of the X-ray sources in the North Ecliptic Pole (NEP) region of the
ROSAT All-Sky Survey and it is the highest redshift cluster
of galaxies of the NEP survey. We have measured spectroscopic
redshifts for twenty cluster galaxies using the Keck-I and the
Canada-France-Hawai'i (CFH) telescopes. The value for the cluster
velocity dispersion is
km s-1.
The cluster was also observed by XMM-Newton. Both the optical and
X-ray data are presented in this paper. The cluster has an unabsorbed
X-ray flux in the 2-10 keV energy band of
erg cm-2 s-1
and a K-corrected luminosity in the same band of
erg s-1
(90% confidence level). The cluster X-ray bolometric luminosity is
erg s-1
(
erg s-1
in the concordance cosmology). The data do not allow fitting both metal
abundance and temperature at the same time.
The abundance is unconstrained and can vary in the range
0.28-1.42
while the best fit X-ray
temperature is
keV. This emission weighted X-ray
temperature is a little lower, barely within the uncertainties,
than the predicted temperature,
keV, from the
relation of local clusters published in the literature.
The optically measured velocity dispersion is consistent with the velocity
dispersion expected from the
relationship.
We also examine the point X-ray source RX J1821.9+6818, or NEP 5330,
located to the south east of the cluster which was identified as a QSO
at
in the ROSAT NEP survey. The X-ray source is well
fitted by an absorbed power law model with
atoms cm-2 and a photon index
typical of an active galactic nucleus.
Key words: galaxies: clusters: general / galaxies: clusters: individual: RX J1821.6+6827 / X-rays: general / X-rays: individuals: RX J1821.6+6827 / X-rays: galaxies: clusters / galaxies: intergalactic medium
© ESO, 2004
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