The Evolution of X-ray Luminous Groups

Tesla JeltemaCarnegie Observatories

J. Mulchaey, L. Lubin, C. Fassnacht, P. Rosati, and H. Böhringer

Sample

• 9 groups selected from the RDCS with 0.2 < z < 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

X-ray Properties

TX = 1.0 – 2.6 keV and L

X(r

500) = 1.5x1043 – 15x1043 ergs/s

Entropy in Groups

These groups show excess entropy similar to low-z systems.

Optical Properties

v = 200-700 km/s from 10-33 members.

Galaxy Populations

Similar to clusters, they have large fractions of early-type galaxies (fe~0.7) and small fractions of galaxies with significant star formation (fOII~0.3).

Galaxy Populations

Similar to clusters, they have large fractions of early-type galaxies (fe~0.7) and small fractions of galaxies with significant star formation (fOII~0.3).

field

field

Central GalaxiesAt low redshift the X-ray emission is peaked on the brightest elliptical

Mulchaey et al. 2003

Central GalaxiesAt low redshift the X-ray emission is peaked on the brightest elliptical

At intermediate redshift …

Mulchaey et al. 2003

Central GalaxiesAt low redshift the X-ray emission is peaked on the brightest elliptical

At intermediate redshift …

Mulchaey et al. 2003

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

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

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

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

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).

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?

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