76 research outputs found
Dark matter and Modified Newtonian Dynamics in a sample of high-redshift galaxy clusters observed with Chandra
We compare the measurement of the gravitational mass of 38 high-redshift
galaxy clusters observed by Chandra using Modified Newtonian Dynamics (MOND)
and standard Newtonian gravity. Our analysis confirms earlier findings that
MOND cannot explain the difference between the baryonic mass and the total mass
inferred from the assumption of hydrostatic equilibrium. We also find that the
baryon fraction at using MOND is consistent with the Wilkinson
Microwave Anisotropy Probe (WMAP) value of Comment: New Astronomy in pres
FUSE Observations of Galactic and Intrinsic Absorption in the Spectrum of the Seyfert 1 Galaxy 2MASX J21362313-6224008
We present the far-ultraviolet spectrum of the Seyfert 1 galaxy 2MASX
J21362313-6224008 obtained with the Far Ultraviolet Spectroscopic Explorer
(FUSE). The spectrum features absorption from Galactic OVI at two velocities
and redshifted HI Lyman beta and gamma, CII, CIII, and O VI. The redshifted
absorption features represent a single kinematic component blueshifted by ~310
km/s relative to the AGN. We use photoionization models to derive constraints
on the physical parameters of the absorbing gas. An alternative interpretation
for the absorption lines is also proposed, whereby the absorbing gas is
associated with an intervening galaxy cluster.Comment: Astrophysical Journal, in pres
Chandra Measurements of a Complete Sample of X-ray Luminous Galaxy Clusters: the Gas Mass Fraction
We present Chandra X-ray measurements of the gas mass fraction out to r500
for a complete sample of the 35 most luminous clusters from the Brightest
Cluster Sample and the Extended Brightest Cluster Sample at redshift
z=0.15-0.30. The sample includes relaxed and unrelaxed clusters, and the data
were analysed independently using two pipelines and two different models for
the gas density and temperature. We measure an average of fgas(r500) = 0.163
+/- 0.032, which is in agreement with the cosmic baryon fraction (Omega_b /
Omega_M = 0.167 +/- 0.006) at the 1-sigma level, after adding the stellar
baryon fraction. Earlier studies reported gas mass fractions significantly
lower than the cosmic baryon fraction at r500, and in some cases higher values
that are consistent with the cosmic baryon fraction towards the virial
radius.In this paper we show that the most X-ray luminous clusters in the
redshift range z=0.15-0.30 have a gas mass fraction that is consistent with the
cosmic value at r500.Comment: MNRAS submitted, comments welcome; 23 pages, 57 figure
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