[show abstract][hide abstract] ABSTRACT: In this paper we analyze the diffuse X-ray coronae surrounding the elliptical galaxy NGC 5846, combining measurements from two observatories, ROSAT and the Advanced Satellite for Cosmology and Astrophysics. We map the gas temperature distribution and find a central cool region within an approximately isothermal gas halo extending to a radius of about 50 kpc and evidence for a temperature decrease at larger radii. With a radially falling temperature profile, the total mass converges to (9.6±1.0)×1012 M☉ at ~230 kpc radius. This corresponds to a total mass to blue light ratio of 53±5 M☉/L☉. As in other early type galaxies, the gas mass is only a few percent of the total mass. Using the spectroscopic measurements, we also derive radial distributions for the heavy elements silicon and iron and find that the abundances of both decrease with galaxy radius. The mass ratio of Si to Fe lies between the theoretical predictions for element production in SN Ia and SN II, suggesting an important role for SN Ia, as well as SN II, for gas enrichment in ellipticals. Using the SN Ia yield of Si, we set an upper limit of 0.012 h250 solar neutrino units (SNU) for the SN Ia rate at radii >50 kpc, which is independent of possible uncertainties in the iron L-shell modeling. We compare our observations with thetheoretical predictions for the chemical evolution of ellipticals. We conclude that the metal content in stars, if explained by the star formation duration, requires a significant decline in the duration of star formation with galaxy radius, ranging from ~1 Gyr at the center to ~0.01 Gyr at 100 kpc radius. Alternatively, the decline in metallicity with galaxy radius may be caused by a similar drop with radius in the efficiency of star formation. Based on the Si and Fe measurements presented in this paper, we conclude that the latter scenario is preferred unless a dependence of the SN Ia rate on stellar metallicity is invoked.
The Astrophysical Journal 01/2009; 514(2):844. · 6.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: We carry out a two-dimensional study of temperature, entropy and pressure distributions in a nearly volume-limited subsample of REFLEX clusters at redshift 0.3, the REFLEX-DXL. We use the observations gained by XMM-Newton, which cover the central 1-2 x r500. We define the substructure in both entropy and pressure as a deviation from the mean profile of the sample. The non-parametric locally weighted regression suggests a broken power law approximation to the entropy profile with inner and outer slopes of 0.78 and 0.52, respectively, and a break at 0.5r500. The characterization of the pressure profile is more complex, requiring three power laws, with slopes -0.64 at r<0.3r500, -2.47 at r>0.5r500 and a slope of -1.50 in between. An analysis of the substructure in the pressure and entropy maps reveals somewhat larger fluctuations around the mean pressure profile compared to the entropy. Typically, pressure fluctuations are found on the 30% level, while the entropy fluctuations are at the 20% level (r.m.s.). We compare the cumulative distribution of the substructure level in the REFLEX-DXL sample with the results of numerical simulation and by means of KS test show that they are in agreement. A discussion of the origin of the substructure is provided on individual cluster basis. Comment: 22 pages, A&A 2005 in press
[show abstract][hide abstract] ABSTRACT: Based on a detailed study of the temperature structure of the intracluster medium in the halo of M 87, abundance profiles of 7 elements, O, Mg, Si, S, Ar, Ca, and Fe are derived. In addition, abundance ratios are derived from the ratios of line strengths, whose temperature dependences are small within the temperature range of the ICM of M 87. The abundances of Si, S, Ar, Ca and Fe show strong decreasing gradients outside 2$'$ and become nearly constant within the radius at ~1.5 solar. The Fe/Si ratio is determined to be 0.9 solar with no radial gradient. In contrast, the O abundance is less than a half of the Si abundance at the center and has a flatter gradient. The Mg abundance is ~1 solar within 2$'$, which is close to stellar abundance within the same radius. The O/Si/Fe pattern of M 87 is located at the simple extension of that of Galactic stars. The observed Mg/O ratio is about 1.25 solar, which is also the same ratio as for Galactic stars. The O/Si/Fe ratio indicates that the SN Ia contribution to Si and Fe becomes important towards the center and SN Ia products have similar abundances of Si and Fe at least around M 87, which may reflect dimmer SN Ia observed in old stellar systems. The S abundance is similar to the Si abundance at the center, but has a steeper gradient. This result suggests that the S/Si ratio of SN II products is much smaller than the solar ratio.