Browsing by Author "Lloyd-Davies, Edward J."

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    Elemental Abundancies in the X-ray Gas of Early-type Galaxies with XMM-Newton and Chandra Observations
    (2009-05-10) Ji, Jun; Irwin, Jimmy A.; Athey, Alex; Bregman, Joel N.; Lloyd-Davies, Edward J.; University of Alabama Tuscaloosa
    The source of hot gas in elliptical galaxies is thought to be due to stellar mass loss, with contributions from supernova (SN) events and possibly from infall from a surrounding environment. This picture predicts supersolar values for the metallicity of the gas toward the inner part of the galaxy, which can be tested by measuring the gas phase abundances. We use high-quality data for 10 nearby early-type galaxy from XMM-Newton, featuring both the European Photon Imaging Camera and the Reflection Grating Spectrometer, where the strongest emission lines are detected with little blending; some Chandra data are also used. We find excellent consistency in the elemental abundances between the different XMM-Newton instruments and good consistency with Chandra. Differences in abundances with aperture size and model complexity are examined, but large differences rarely occur. For a twotemperature thermal model plus a point source contribution, the median Fe and O abundances are 0.86 and 0.44 of the solar value, while Si and Mg abundances are similar to that for Fe. This is similar to stellar abundances for these galaxies but SNe were expected to enhance the gas phase abundances considerably, which is not observed.
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    X-Ray Searches for Emission from the Whim in the Galactic Halo and the Intergalactic Medium
    (2009-07-10) Bregman, Joel N.; Otte, Birgit; Irwin, Jimmy A.; Putman, Mary E.; Lloyd-Davies, Edward J.; Bruns, Christian; University of Alabama Tuscaloosa
    At least 50% of the baryons in the local universe are undetected and predicted to be in a hot dilute phase (105–107 K) in low and moderate overdensity environments. We searched for the predicted diffuse faint emission through shadowing observations whereby cool foreground gas absorbs more distant diffuse emission. Observations were obtained with Chandra and XMM-Newton. Using the cold gas in two galaxies, NGC 891 and NGC 5907, shadows were not detected and a newer observation of NGC 891 fails to confirm a previously reported X-ray shadow. Our upper limits lie above model predictions. For Local Group studies, we used a cloud in the Magellanic Stream and a compact high-velocity cloud to search for a shadow. Instead of a shadow, the X-ray emission was brighter toward the Magellanic Stream cloud and there is a less significant brightness enhancement toward the other cloud also. The brightness enhancement toward the Magellanic Stream cloud is probably due to an interaction with a hot ambient medium that surrounds the Milky Way. We suggest that this interaction drives a shock into the cloud, heating the gas to X-ray emitting temperatures.