X-rays from Elliptical Galaxies

1
X-rays from Elliptical Galaxies
Ross Collins with Ewan OSullivan
(CfA) Trevor Ponman (Birmingham)

• Outline
• Motivation
• ROSAT Data Analysis
• Results

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Motivation

• Galaxy Clusters Groups

• Hot Gas Haloes
• Dark Matter Haloes
• Scaling

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Sample Selection

• From a database of 100,000 nearby galaxies
• Morphological T-type lt -2 (i.e. early-types S0s
  and Es)
• Absolute magnitude MB lt -19
• Virgocentric flow corrected recession velocity
  vrec lt 10,500 km s-1
• ROSAT PSPC observation within 30 of pointing,
  and exposures gt 10 ksec
• Result 39 large, X-ray luminous early-type
  galaxies

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ROSAT PSPC

• Data Cube
• Data Reduction

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Cluster Contamination

• Radial profile of galaxy
• Spectral fit -gt re-process background to include
  cluster emission
• SB fit include cluster emission and model
  separately.

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X-ray Optical Overlays - ROI
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Fossil Group Galaxy NGC 6482
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Reduced Data
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Surface Brightness Profiles

• Profiles fitted by 2D multi-component King,
  point-source, and de Vacouleurs r1/4 models,
  representing
• galactic halo (single King)
• AGN galactic halo (point King)
• galactic halo stellar emission (King de
  Vacouleurs)
• galactic halo cluster halo (double King)
• gt Halo Luminosity

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Spectral Fits

• Compared using Cash statistic
• MEKAL hot plasma (4 parameters)
• 7 keV Bremsstrahlung MEKAL
• Power-law MEKAL
• Gas Temperature
• Z (unreliable)
• X-ray Flux (halo stellar)

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Temperature Profiles
Very varied Isothermal
Hot Cores Cooling cores
(25 ) (15 )
(60 )
AGN?
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The LX T Relation

• Central Cooling
• Central Heating
• Isothermal
• Unclassified
• Under-luminous galaxies due to cluster obscuration

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Comparison with Groups Clusters

• Galaxy Halos
• Group Halos
• Cluster Halos

Same slope as for groups, but offset to lower
luminosities (factor of 3)
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LX LB s T Relations
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Possible Interpretations

• s T relation identical to clusters both are
  good measures of the depth of the potential well
• LX - T relation is same for both galaxies with
  and without a cooling core, suggesting cooling
  flows are not dominant
• Offsets in the other relationships suggest that
  galaxy halos and group/cluster halos are formed
  by different processes.
• Future XMM Chandra