Galaxy mass-to-light ratios at z> 1 from the Fundamental Plane: measuring the star formation epoch and mass evolution of galaxies van der Wel, Rix, Franx, van Dokkum, Rosati, Illingworth, Holden

Galaxy formation through merging

How to test for merging ? measure mass evolution from: luminosity function evolution of mass-to-light ratios Critical test for hierarchical galaxy formation !

Measuring mass-to-light ratios Use Fundamental Plane relation with low scatter: few measurements needed M/L evolution depends on formation redshift of stars Critical test for hierarchical galaxy formation !

Goal of our program: Measure M/L evolution beyond z=1 for both clusters and field early types (state-of-the art was z=0.8 for clusters and z=0.6 for field) Critical test for hierarchical galaxy formation !

Required Deep FORS2 spectroscopy in the red (4000 A break to A) hours integration time Deep HST ACS z-band imaging CDF-South and MS1252 very deep imaging relation with low scatter: few measurements needed M/L evolution depends on formation redshift of stars Critical test for hierarchical galaxy formation !

Large Programme Requested: 12 nights of VLT time (Sept 02 – June 03) Bad weather first 2 visitor runs but were able to find and solve mask alignment problems Deep HST ACS z-band imaging CDF-South and MS1252 very deep imaging relation with low scatter: few measurements needed M/L evolution depends on formation redshift of stars Critical test for hierarchical galaxy formation !

Large Programme Runs in 2003 very succesful, including extra run in Sept to compensate for bad weather in 02

Results: Slow evolution for cluster galaxies

faster evolution for the field

But: Massive field galaxies evolve as slowly as massive cluster galaxies best fitting formation redshifts above z=2 ! The jury is still out on the lower mass galaxies: contradictory earlier results can be explained by selection effects

Hierarchical models fail completely: generally predict large difference between field galaxies and cluster galaxies Some mechanism shuts off star formation very early for massive early-type galaxies AGN ?

Conclusions: Large programme worked very well (despite 1 year delay on field sample) Allowed us to get a lot of hands- on experience in very short time Fors 2 is a great resource Next step is to higher redshifts...

Papers van der Wel et al 2004 (submitted 2003) ApJ L 5-8 The Fundamental Plane of Field Early-type galaxies at z=1 van der Wel et al 2005 (submitted 2004) ApJ accepted. Full data and analysis paper of fundamental plane of field galaxies Holden et al 2005, ApJ L 620, 583 (submitted 2004): Fundamental Plane of cluster ellipticals at z=1.25 several more analysis papers in progress (PhD van der Wel)

M/L B ~M 0.26 Local B-band FP of Cluster Galaxies

Evolution of the cluster FP

Cluster galaxies out to z = 1.27: Δ ln (M/L B ) / z = /  formation redshift of z ~ 3 van Dokkum & Franx 1996, van Dokkum et al. 1998, Kelson et al. 2000, van Dokkum & Stanford 2003, Wuyts et al. 2004, Holden et al Hierarchical galaxy formation models: field galaxies are younger Results have been contradictory for the past 5 years. This was the main science driver for the LP.

Observations ( FORS2 on VLT, 600z grism, ~5.5Å FWHM resolution ) 42 velocity dispersions measured -4 CL1252 early-type cluster galaxies (z = 1.24) -20 field early-type galaxies at z ~ 1 in the CDFS -18 lower-z field early-types and z ~ 1 late types in the CL 1252 field and the CDFS 29 of the field galaxies have early-type morphologies and spectra with S/N>12

Misalignment – through slit images ROTATION!! After alignment with reference stars (standard ESO procedure) slits are not well aligned: 1.5 pixels off at bottom of FOV Manual rotation required by 0.06 degrees at telescope control Up to ~25% of flux might be missed in a 1 arcsec slit! normal slit with galaxy square ´slit´ with star

Rest-frame Wavelength (Å) Spectra: two examples

v,i,z color images and profile-fitting residuals

M/L evolution of field galaxies

A correlation between M/L and color

Equally massive galaxies in different environments evolve equally fast: massive field galaxies are not younger than massive cluster galaxies. Low mass galaxies evolve faster than high mass galaxies (i.e., high mass galaxies are older), an effect that cannot be entirely explained by selection effects. Earlier contradictory results explained largely by differences between the methods to measure the evolution. Conclusions