Searcharxiv⌕ Search
Home/Archive/arXiv

arXiv · astro-ph/0408028

RXJ 1821.6+6827: a Cool Cluster at z=0.81 from the ROSAT NEP Survey

I. M. Gioia·A. Wolter·C. R. Mullis·J. P. Henry·H. Boehringer·U. G. Briel
View original source ↗Read source document ↗Export metadata ↓

Abstract

We present an analysis of the properties of the cluster of galaxies RXJ 1821.6+6827, or NEP 5281, at a redshift z=0.816+/-0.001. RXJ 1821.6+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 sigma_V=775(+182,-113) 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 F(2-10 keV)=1.24(+0.16,-0.23) x 10-13 erg cm2 s-1 and a K-corrected luminosity in the same band of L(2-10 keV)=6.32(+76,-0.73)x10^44 h_50^-2 erg s-1 (90% confidence level). The cluster X-ray bolometric luminosity is L(BOL,X)=1.35(+0.08,-0.21)x10^45 h_50^-2 erg s-1. 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 Z_sun while the best fit X-ray temperature is T=4.7(+1.2,-0.7) keV. This emission weighted X-ray temperature is a little lower, barely within the uncertainties, than the predicted temperature, T=6.34(+0.13,-0.35) keV, from the L_X-T_X relation of local clusters published in the literature. The optically measured velocitydispersion is consistent with the velocity dispersion expected from the sigma_V-T_X relationship. We also examine the point X-ray source RXJ1821.9+6818, or NEP 5330, located to the south east of the cluster which was identified as a QSO at z=1.692+/-0.008 in the ROSAT NEP survey.

Explore related subjects

astro-ph

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

I. M. Gioia, A. Wolter, C. R. Mullis, J. P. Henry, H. Boehringer, U. G. Briel. 2004-08-02. RXJ 1821.6+6827: a Cool Cluster at z=0.81 from the ROSAT NEP Survey. https://doi.org/10.1051/0004-6361%3A20041426

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Frame covariance of CMBR lensing in the exact 1+3 covariant radiation hierarchy

The exact $1+3$ covariant Boltzmann hierarchy for the cosmic microwave background contains acceleration, shear and vorticity couplings whose coefficients grow linearly in $\ell$. We show that all are the multipole form of the aberration operator in the photon Liouville equation. Under a change of threading, this operator shifts by the along-ray generator of a Lorentz boost. The acceleration coupling of $\ell$ to $\ell\pm1$ and the shear coupling of $\ell$ to $\ell\pm2$ are therefore frame-covariant descriptions of the same operator, related by an algebraic, pointwise relabelling of direction. With emitter and observer frames fixed, the observed sky is independent of the intermediate threading at every $\ell$. We derive this in $1+3$ covariant and gauge-invariant variables without constructing second-order gauge-invariant variables. The $O(ε^2\ell)$ content is gravitational lensing, as known in metric variables. Linearisation about a Friedmann--Lemaître--Robertson--Walker background removes these couplings, requiring lensing to be reinstated from the geodesic equation. Keeping the threading arbitrary makes frame covariance explicit and places observer aberration in the same operator. In the Newtonian threading we compute both halves of the deflection: the equivalence-principle contribution enters through aberration, while the spatial-curvature contribution arises from free streaming on perturbed spatial sections and reduces to the same operator. The lensing efficiency follows from the direction derivative. The angular-power-spectrum contribution is quartic in the potential: for a deflection statistically independent of the source, the two fourth-order terms carrying $\ell^2$ cancel where the spectrum is smooth on the deflection scale, and lensing redistributes power without adding ensemble variance.

astro-ph↗
arXiv2026

Cosmic Conundrums with Quantum Corrections

Darh energy was discovered over 25 years ago and we do not have an explanation of it. Dark matter comprises 95% of matter in the universe and we still don't know what it is. The Webb telescope has been finding fully formed galaxies with massive black holes millions of times the mass of the sun in the early universe and we don't have any explanation. A quantum density limitation will be used to solve these and other outstanding problems.

astro-ph↗
arXiv2026

On binary pulsars and the force of gravity

The energy-momentum budget of the astrophysical systems can be studied by the exact local conservation equation derived by Landau and Lifshitz. We show that a similar equation is valid for the Einstein-Cartan gravity. We reanalyze a binary pulsar system using the Landau-Lifshitz conservation equation and show that the orbital period change rate can be completely understood as a curvature backreaction process. Taking into account the detailed theoretical and observational research of relativistic binary pulsar systems, especially the system of Hulse and Taylor, we conclude that general relativity and astrophysical observations rule out the existence of gravitational radiation. We comment upon the LIGO GW events and their alternative explanation, as well as the recent pulsar timing arrays data.

astro-ph↗