Trevor J. Ponman

X-ray luminosities of galaxies in groups

We have derived the X-ray luminosities of a sample of galaxies in groups, making careful allowance for contaminating intragroup emission. The L_X:L_B and L_X:L_{FIR} relations of spiral galaxies in groups appear to be indistinguishable from those in other environments, however the elliptical galaxies fall into two distinct classes. The first class is central-dominant group galaxies which are very X-ray luminous, and may be the focus of group cooling flows. All other early-type galaxies in groups belong to the second class, which populates an almost constant band of L_X/L_B over the range 9.8 < log L_B < 11.3. The X-ray emission from these galaxies can be explained by a superposition of discrete galactic X-ray sources together with a contribution from hot gas lost by stars, which varies a great deal from galaxy to galaxy. In the region where the optical luminosity of the non-central group galaxies overlaps with the dominant galaxies, the dominant galaxies are over an order of magnitude more luminous in X-rays. nWe also compared these group galaxies with a sample of isolated early-type galaxies, and used previously published work to derive L_X:L_B relations as a function of environment. The non-dominant group galaxies have mean L_X/L_B ratios very similar to that of isolated galaxies, and we see no significant correlation between L_X/L_B and environment. We suggest that previous findings of a steep L_X:L_B relation for early-type galaxies result largely from the inclusion of group-dominant galaxies in samples.

X-Ray Measurements of the Mass Profiles in Massive Isolated Elliptical Galaxies

We discuss some results for mass profiles that we have obtained from hydrostatic studies of the hot gas in isolated, massive elliptical galaxies.

XMM-Newton survey of IGM: news for the modified entropy scaling

Results of XMM-Newton survey of 40 galaxy groups will be presented with accent on the global properties of the gas, such as entropy and pressure. We confirm the modified entropy scaling relation of Ponman, Sanderson & Finoguenov (2003) at central parts of the groups (0.1 · r500). The slopes of the entropy profiles of the groups are on average flatter than 1.1 law, typical of the clusters. We present the results of numerical simulations using the GADGET-II code, which are the first simulations capable to reproduce these newly observed trends.