An XMM-Newton observation of the galaxy group MKW 4

We present an X-ray study of the galaxy group or poor cluster MKW 4. Working with XMM-Newton data we examine the distribution and properties of the hot gas which makes up the group halo. The inner halo shows some signs of structure, with circular or elliptical beta models providing a poor fit to the surface brightness profile. This may be evidence of large-scale motion in the inner halo, but we do not find evidence of sharp fronts or edges in the emission. The temperature of the halo declines in the core, with deprojected spectral fits showing a central temperature of similar to1.3 keV compared to similar to3 keV at 100 kpc. In the central similar to30 kpc of the group, multitemperature spectral models are required to fit the data, but they indicate a lack of gas at low temperatures. Steady-state cooling flow models provide poor fits to the inner regions of the group and the estimated cooling time of the gas is long except within the central dominant galaxy, NGC 4073. Abundance profiles show a sharp increase in the core of the group, with mean abundance rising by a factor of 2 in the centre of NGC 4073. Fitting individual elements shows the same trend, with high values of Fe, Si and S in the core. We estimate that similar to50 per cent of the Fe in the central 40 kpc was injected by Type Ia supernovae, in agreement with previous ASCA studies. Using our best-fitting surface brightness and temperature models, we calculate the mass, gas fraction, entropy and mass-to-light ratio of the group. At 100 kpc (similar to0.1 virial radius) the total mass and gas entropy of the system (similar to2 x 10(13) M-. and similar to300 keV cm(2)) are quite comparable to those of other systems of similar temperature, but the gas fraction is rather low (similar to1 per cent). We conclude that MKW 4 is a fairly relaxed group, which has developed a strong central temperature gradient but not a large-scale cooling flow.