We present the concentration ( c ) -virial mass ( M ) relation of 39 galaxy systems ranging in mass from individual early-type galaxies up to the most massive galaxy clusters , ( 0.06 - 20 ) \times 10 ^ { 14 } \hbox { { $M _ { \odot } $ } } .
We selected for analysis the most relaxed systems possessing the highest quality data currently available in the Chandra and XMM public data archives .
A power-law model fitted to the X-ray c - M relation requires at high significance ( 6.6 \sigma ) that c decreases with increasing M , which is a general feature of CDM models .
The median and scatter of the c - M relation produced by the flat , concordance \Lambda CDM model ( \hbox { { $ \Omega _ { m } $ } } = 0.3 , \hbox { { $ \sigma _ { 8 } $ } } = 0.9 ) agrees with the X-ray data provided the sample is comprised of the most relaxed , early forming systems , which is consistent with our selection criteria .
Holding the rest of the cosmological parameters fixed to those in the concordance model the c - M relation requires 0.76 < \hbox { { $ \sigma _ { 8 } $ } } < 1.07 ( 99 % conf .
) , assuming a 10 % upward bias in the concentrations for early forming systems .
The tilted , low- \sigma _ { 8 } model suggested by a new WMAP analysis is rejected at 99.99 \% confidence , but a model with the same tilt and normalization can be reconciled with the X-ray data by increasing the dark energy equation of state parameter to w \approx - 0.8 .
When imposing the additional constraint of the tight relation between \sigma _ { 8 } and \Omega _ { m } from studies of cluster abundances , the X-ray c - M relation excludes ( > 99 \% conf . )
both open CDM models and flat CDM models with \hbox { { $ \Omega _ { m } $ } } \approx 1 .
This result provides novel evidence for a flat , low- \Omega _ { m } universe with dark energy using observations only in the local ( z \ll 1 ) universe .
Possible systematic errors in the X-ray mass measurements of a magnitude \approx 10 \% suggested by CDM simulations do not change our conclusions .
We discuss other sources of systematic error in the measurements and theoretical predictions that need to be addressed for future precision cosmological studies using the c - M relation .