X-ray Selected Intermediate-Redshift Groups

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Sample

• 9 groups selected from the RDCS with 0.2 lt z lt
  0.6.
• Optical Observations
• Initial spectroscopy with Palomar and Las
  Campanas
• Spectroscopy with Keck and Gemini for 7 groups
• Imaging with WFPC2 on HST
• X-ray Observations
• XMM observations for 6 groups
• Additional Chandra and XMM coming

Jeltema et al. 2006a Mulchaey et al. 2006
Jeltema et al. 2006b
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X-ray Properties

• TX 1.0 2.6 keV and LX(r500) 1.5x1043
  15x1043 ergs/s

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Optical Properties

• ?v 200-700 km/s from 10-33 members.

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Galaxy Populations
Similar to clusters, they have large fractions of
early-type galaxies (fe0.7) and small fractions
of galaxies with significant star formation
(fOII0.3).
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Galaxy Populations
field
field
Similar to clusters, they have large fractions of
early-type galaxies (fe0.7) and small fractions
of galaxies with significant star formation
(fOII0.3).
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Central Galaxies
At low redshift the X-ray emission is peaked on
the brightest elliptical
Mulchaey et al. 2003
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Central BGGs

• z 0.41
• ? 302 km/s,
• T 1.9 keV
• X-ray and BGG align
• z 0.59
• ? 682 km/s,
• T 2.6 keV
• fe 0.38, fOII 0.43
• BGG small secondary

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Multiple component BGGs

• z 0.23
• ? 570 km/s,
• T 2.6 keV
• Secondary in group
• z 0.23
• ? 595 km/s,
• T 2.4 keV
• MV,2- MV,1 1.5

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Offset BGGs

• z 0.38
• ? 246 km/s,
• T 1.7 keV
• BGG E, E pair
• RBGG 110 kpc
• z 0.38
• ? 417 km/s,
• T 1.0 keV
• String ? 194 km/s

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Other Groups

• z 0.46
• ? 211 km/s
• fe 0.43, fOII 0.67
• BGG offset in velocity

• z 0.31
• ? 632 km/s
• fe 0.27
• Spiral BGG

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BGG Formation

• None of the central galaxies, including those
  with multiple components, show significant OII
  emission.
• Consistent with late formation of BGGs through
  gas-poor mergers.
• Late BCG formation seen in simulations (De Lucia
  Blaizot 2006 Dubinski 1998).

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Summary

• The X-ray properties of these groups are similar
  to low-z groups.
• They appear to follow the scaling relations
  between L, T, and ???and they show excess entropy
  over self-similar predictions.
• We do not observe a strong evolution in the
  galaxy populations from X-ray luminous low-z
  groups.
• They have large fractions of early-type galaxies
  and small fractions of galaxies with significant
  star formation.
• However, the galaxy populations vary between
  groups.
• Unlike low-z, X-ray luminous groups, we do not
  generally find a single, dominant BGG at the
  center of these groups. Late BGG
  formation?

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Future

• Upcoming observations with Chandra and XMM
• High-resolution spectroscopy and simulations of
  multiple component BGGs
• X-ray and optical follow up of a large, X-ray
  selected sample of groups at low-redshift