J/MNRAS/393/1467 Field early-type galaxies at 0.2 =2009MNRAS.393.1467F ================================================================================ ADC_Keywords: Galaxies, photometry ; Photometry, UBVRI ; Velocity dispersion ; Redshifts Keywords: galaxies: elliptical and lenticular, cD - galaxies: evolution - galaxies: formation - galaxies: kinematics and dynamics - galaxies: stellar content - cosmology: observations Abstract: We explore the properties of 24 field early-type galaxies in the redshift range 0.20=-0.74+/-0.08. The M/L evolution of these field galaxies suggests a continuous mass assembly of field early-type galaxies during the last 5Gyr, that gets support by recent studies of field galaxies up to z~1. Independent evidence for recent star formation activity is provided by spectroscopic (OII emission, Hdelta) and photometric (rest-frame broad-band colors) diagnostics. Based on the Hdelta absorption feature we detect a weak residual star formation for galaxies that accounts for 5%-10% in the total stellar mass of these galaxies. The co-evolution in the luminosity and mass of our galaxies favours a downsizing formation process. We find some evidence that our galaxies experienced a period of star formation quenching, possible triggered by AGN activity that is in good agreement with recent results on both observational and theoretical side. Description: Structural parameters, coordinates, redshifts, luminosities, colours, dynamical masses, M/L ratios and velocity dispersions are presented for a sample of 24 field early-type galaxies in the FORS Deep Field and the William Herschel Deep Field. The galaxies cover the redshift range 0.2 ?=- Seeing corrected mean surface brightness within reff in Johnson B-band 84- 87 F4.2 mag/arcsec2 e_ ?=- Error on 89- 93 F5.2 solMass logMdyn ?=- Log10 dynamical mass 95- 98 F4.2 solMass e_logMdyn ?=- Error on logMdyn 100-103 F4.2 Sun logM/L ?=- Log10(M/L) in Johnson B-band (5) 105-109 F5.2 --- dlnM/L ?=- {Delta}LN(M/L) in Johnson B-band 111-114 F4.2 --- e_dlnM/L ?=- Error on Delta dlnM/L 116-120 F5.2 mag B-I Rest-frame extinction-corrected B-I colour index -------------------------------------------------------------------------------- Note (1): Nomenclature note: WHDF NNNa identified as [FBZ2009] WHDF-NNNa in Simbad Note (2): Velocity dispersions are not corrected for aperture effects. Note (3): Signal-to-noise ratio per Angstroem in rest-frame. One pixel is 1.6{AA}. Note (4): Structural parameters were derived from 2-D surface brightness profile fitting on HST/ACS images taking into account distortion and PSF variation effects. Note (5): The error on M/L ratio (in solar units) is the same as the error on the dynamical mass Mdyn. -------------------------------------------------------------------------------- Acknowledgements: Alexander Fritz, afritz (at)gemini.edu References: Metcalfe et al., 2001MNRAS.323..795M, UBRI photometry in the William Herschel Deep Field ================================================================================ (End) Patricia Vannier [CDS] 30-Oct-2009