The scatter and evolution of the color-magnitude relation
of elliptical galaxies
Christine RuhlandChristine Ruhland
MPIA Students Workshop March 2007MPIA Students Workshop March 2007
Christine Ruhland - The color-magnitude relation
• Elliptical galaxies:Elliptical galaxies:• old stellar populationsold stellar populations• no star formationno star formation• Tight relation in the CMD - red sequenceTight relation in the CMD - red sequence
Introduction – Elliptical galaxies
Christine Ruhland - The color-magnitude relation
0.2
1.2
0.4 0.6 0.8 1.0
1.95
formation redshift = 2
truncation redshifts
Introduction - Truncation models
Christine Ruhland - The color-magnitude relation
• Measurement of the scatter of the CMR Measurement of the scatter of the CMR (formation epoch)(formation epoch)
• 2 requirements:2 requirements:• Well-measured colorsWell-measured colors• Spectroscopic redshifts Spectroscopic redshifts
(good k-corrections)(good k-corrections)
Introduction - Goals
Christine Ruhland - The color-magnitude relation
Data – GEMS and the spectroscopic redshifts
• Spectroscopic Spectroscopic redshift sample of redshift sample of 2138 objects2138 objects
• three redshift bins three redshift bins used to make used to make CMDsCMDs
531
269
191
Christine Ruhland - The color-magnitude relation
• measurement of flux inside of the half light measurement of flux inside of the half light radius for the two GEMS filters v (606 nm) and radius for the two GEMS filters v (606 nm) and z (920 nm)z (920 nm)
• K-correction to get other filter bandsK-correction to get other filter bands
Method
Christine Ruhland - The color-magnitude relation
Christine Ruhland - The color-magnitude relation
Results – measurement of scatter and zeropoints in the CMD
• u-g over Mu-g over Mgg at at z = 0.1 calculated z = 0.1 calculated with restframe gridwith restframe grid
• Additional SDSS Additional SDSS data for z = 0.05data for z = 0.05
n < 2.5n < 2.5
n > 2.5AND redn > 2.5
AND red
MIPS24µm IR
MIPS24µm IR
X-rayX-ray
blueblue
Christine Ruhland - The color-magnitude relation
Sérsic profile
• Profile describing the surface brightness of Profile describing the surface brightness of galaxiesgalaxies
• Sérsic index nSérsic index n• n ~ 1 for disks (exponetial profile)n ~ 1 for disks (exponetial profile)• The higher the steeper the inner part of the The higher the steeper the inner part of the
profileprofile• n = 4 for bulges (deVaucouleurs profile)n = 4 for bulges (deVaucouleurs profile)
1/ /1
)( n
erreer 1/ /1
)( n
erreer
Christine Ruhland - The color-magnitude relation
Results – measurement of scatter and zeropoints in the CMD
• u-g over Mu-g over Mgg at z = 0.1 at z = 0.1 calculated with calculated with restframe gridrestframe grid
• Additional SDSS data Additional SDSS data for z = 0.05for z = 0.05
• REAL error bars, i.e., REAL error bars, i.e., we measure the scatterwe measure the scatter
Christine Ruhland - The color-magnitude relation
Comparison with truncation models
Christine Ruhland - The color-magnitude relation
0.2
1.2
0.4 0.6 0.8 1.0
1.95
formation redshift = 2
truncation redshifts
Truncation models
Christine Ruhland - The color-magnitude relation
More complex truncation models• Galaxies with different truncation redshifts and Galaxies with different truncation redshifts and
metallicities (distributed around solar metallicity)metallicities (distributed around solar metallicity)
583
24
34
93
Christine Ruhland - The color-magnitude relation
Conclusion
• Red sequence has build up over a longer Red sequence has build up over a longer period of timeperiod of time
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