GINGA OBSERVATIONS OF ABELL-2218 - IMPLICATIONS FOR H0

GINGA observations of the cluster of galaxies Abell 2218 show that its spectrum is well fitted by an isothermal model with temperature 6.7+0.5-0.4 keV. Abell 2218 is the cluster in whose direction the Sunyaev-Zel'dovich effect has been searched for most intensively. Assuming a value of -0.69 ±0.10 mK for the central SZ decrement (Birkinshaw), and calculating the radial gas density distribution by deprojecting the X-ray surface brightness, we derive a value for the Hubble constant, for a uniform cluster gas, H0=24+13-10 km s-1 Mpc-1. Possible reasons for the discrepancy between this value and the currently accepted higher values derived with other techniques are explored. © Royal Astronomical Society. Provided by the NASA Astrophysics Data System.