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Register a new userXMM-Newton First-Light Observations of the Hickson Galaxy Group 16
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M. J. L. Turner
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This paper presents the XMM-Newton first-light observations of the Hickson-16 compact group of galaxies. Groups are possibly the oldest large-scale structures in the Universe, pre-dating clusters of galaxies, and are highly evolved. This group of small galaxies, at a redshift of 0.0132 (or 80 Mpc) is exceptional in the having the highest concentration of starburst or AGN activity in the nearby Universe. So it is a veritable laboratory for the study of the relationship between galaxy interactions and nuclear activity. Previous optical emission line studies indicated a strong ionising continuum in the galaxies, but its origin, whether from starbursts, or AGN, was unclear. Combined imaging and spectroscopy with the EPIC X-ray CCDs unequivocally reveals a heavily obscured AGN and a separately identified thermal (starburst) plasma, in NGC 835, NGC 833 and NGC 839. NGC 838 shows only starburst thermal emission. Starbursts and AGN can evidently coexist in members of this highly evolved system of merged and merging galaxies, implying a high probability for the formation of AGN as well as starbursts in post-merger galaxies.
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We present an X-ray study of the galaxy group RGH 80, observed by XMM-Newton. The X-ray emission of the gas is detected out to ~ 462h^{-1}_{50} kpc, corresponding to ~ 0.45 r_{200}. The group is relatively gas rich and luminous with respect to its temperature of 1.01 +/- 0.01 keV. Using the deprojected spectral analysis, we find that the temperature peaks at ~ 1.3 keV around 0.11r_{200}, and then decreases inwards to 0.83 keV at the center and outwards to ~ 70% of the peak value at large radii. Within the central ~ 60 kpc of the group where the gas cooling time is less than the Hubble time, two-temperature model with temperatures of 0.82 and 1.51 keV and the Galactic absorption gives the best fit of the spectra, with ~ 20% volume occupied by the cool component. We also derive the gas entropy distribution, which is consistent with the prediction of cooling and/or internal heating models. Furthermore, the abundances of O, Mg, Si, S, and Fe decrease monotonically with radius. With the observed abundance ratio pattern, we estimate that ~ 85% or ~ 72% of the iron mass is contributed by SN Ia, depending on the adopted SN II models.
In an XMM-Newton raster observation of the bright Local Group spiral galaxy M 33 we study the population of X-ray sources (X-ray binaries, supernova remnants) down to a 0.2--4.5 keV luminosity of 10^35 erg/s -- more than a factor of 10 deeper than earlier ROSAT observations. EPIC hardness ratios and optical and radio information are used to distinguish between different source classes. The survey detects 408 sources in an area of 0.80 square degree. We correlate these newly detected sources with earlier M 33 X-ray catalogues and information from optical, infra-red and radio wavelengths. As M 33 sources we detect 21 supernova remnants (SNR) and 23 SNR candidates, 5 super-soft sources, and 2 X-ray binaries (XRBs). There are 267 sources classified as hard, which may either be XRBs or Crab-like SNRs in M 33 or background AGN. The 44 confirmed and candidate SNRs more than double the number of X-ray detected SNRs in M 33. 16 of these are proposed as SNR candidates from the X-ray data for the first time. On the other hand, there are several sources not connected to M 33: five foreground stars, 30 foreground star candidates, 12 active galactic nucleus candidates, one background galaxy and one background galaxy candidate. Extrapolating from deep field observations we would expect 175 to 210 background sources in this field. This indicates that about half of the sources detected are sources within M 33.
XMM-Newton has observed the X-ray sky since early 2000. The XMM-Newton Survey Science Centre Consortium has published catalogues of X-ray and ultraviolet sources found serendipitously in the individual observations. This series is now augmented by a catalogue dedicated to X-ray sources detected in spatially overlapping XMM-Newton observations. The aim of this catalogue is to explore repeatedly observed sky regions. It thus makes use of the long(er) effective exposure time per sky area and offers the opportunity to investigate long-term flux variability directly through the source detection process. A new standardised strategy for simultaneous source detection on multiple observations is introduced. It is coded as a new task within the XMM-Newton Science Analysis System and used to compile a catalogue of sources from 434 stacks comprising 1,789 overlapping XMM-Newton observations that entered the 3XMM-DR7 catalogue, have a low background and full-frame readout of all EPIC cameras. The first stacked catalogue is called 3XMM-DR7s. It contains 71,951 unique sources with positions and parameters such as fluxes, hardness ratios, quality estimates, and information on inter-observation variability. About 15% of the sources are new with respect to 3XMM-DR7. Through stacked source detection, the parameters of repeatedly observed sources can be determined with higher accuracy than in the individual observations. The method is more sensitive to faint sources and tends to produce fewer spurious detections. With this first stacked catalogue we demonstrate the feasibility and benefit of the approach. It supplements the large data base of XMM-Newton detections by additional, in particular faint, sources and adds variability information. In the future, the catalogue will be expanded to larger samples and continued within the series of serendipitous XMM-Newton source catalogues.
Using new XMM and Chandra observations we present an analysis of the metal abundances of the hot gas within a radius of 100 kpc of the bright nearby galaxy group NGC 5044. Motivated by the inconsistent abundance and temperature determinations obtained by different observers for X-ray groups, we provide a detailed investigation of the systematic errors on the derived abundances considering the effects of the temperature distribution, calibration, plasma codes, bandwidth, Galactic Nh, and background rate. The iron abundance (Fe) drops from Fe ~1 solar within R ~50 kpc to Fe ~0.4 solar near R=100 kpc. This radial decline in Fe is highly significant: Fe=1.09 +/- 0.04 solar (stat) +/- 0.05 solar + 0.18 solar (sys) within R=48 kpc (5) compared to Fe=0.44 +/- 0.02 solar (stat) +/- 0.10 solar + 0.13 solar (sys) over R=48-96 kpc (5-10). The data rule out with high confidence a very sub-solar value for Fe within R=48 kpc confirming that previous claims of very sub-solar central Fe values in NGC 5044 were primarily the result of the Fe Bias: i.e., the incorrect assumption of spatially isothermal and single-phase gas when in fact temperature variations exist. Within R=48 kpc we obtain Si/Fe = 0.83 +/- 0.02 (stat) +/- 0.02 + 0.07 (sys) and S/Fe = 0.54 +/- 0.02 (stat) +/- 0.01 + 0.01 (sys) in solar units. These ratios are consistent with their values at larger radii and imply that SNIa have contributed ~80% of the iron mass within a 100 kpc radius of NGC 5044. This SNIa fraction is similar to the Sun and suggests an IMF similar to that of the Milky Way. At the very center (R ~2 kpc) the XMM and Chandra CCDs and the XMM RGS show that the Fe drops to ~50% of its value at immediately larger radius analogously to that seen in some galaxy clusters. (Abridged)
We studied the intracluster medium of the galaxy cluster CIZA J2242.8+5301 using deep XMM-Newton observations. The cluster hosts a remarkable 2-Mpc long, ~50-kpc wide radio relic that has been nicknamed the Sausage. A smaller, more irregular counter-relic is also present, along with a faint giant radio halo. We analysed the distribution of the ICM physical properties, and searched for shocks by trying to identify density and temperature discontinuities. East of the southern relic, we find evidence of shock compression corresponding to a Mach number of 1.3, and speculate that the shock extends beyond the length of the radio structure. The ICM temperature increases at the northern relic. More puzzling, we find a wall of hot gas east of the cluster centre. A partial elliptical ring of hot plasma appears to be present around the merger. While radio observations and numerical simulations predict a simple merger geometry, the X-ray results point towards a more complex merger scenario.
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