SPIDER – I. Sample and galaxy parameters in the grizYJHK wavebands

This is the first paper of a series presenting the Spheroids Panchromatic Investigation in Different Environmental Regions (SPIDER). The sample of spheroids consists of 5080 bright (Mr < −20) early-type galaxies (ETGs), in the redshift range of 0.05 to 0.095, with optical (griz) photometry and spectroscopy from the Sloan Digital Sky Survey Data Release 6 (SDSS-DR6) and near-infrared (YJHK) photometry from the UKIRT Infrared Deep Sky Survey-Large Area Survey (UKIDSS-LAS) (DR4). We describe how homogeneous photometric parameters (galaxy colours and structural parameters) are derived using grizYJHK wavebands. We find no systematic steepening of the colour–magnitude relation when probing the baseline from g−r to g−K, implying that internal colour gradients drive most of the mass–metallicity relation in ETGs. As far as structural parameters are concerned we find that the mean effective radius of ETGs smoothly decreases, by 30 per cent, from g through K, while no significant dependence on waveband is detected for the axial ratio, Sersic index and a4 parameters. Furthermore, velocity dispersions are remeasured for all the ETGs using starlight and compared to those obtained by SDSS. The velocity dispersions are rederived using a combination of simple stellar population models as templates, hence accounting for the kinematics of different galaxy stellar components. We compare our (2dphot) measurements of total magnitude, effective radius and mean surface brightness with those obtained as part of the SDSS pipeline (photo). Significant differences are found and reported, including comparisons with a third and independent part. A full characterization of the sample completeness in all wavebands is presented, establishing the limits of application of the characteristic parameters presented here for the analysis of the global scaling relations of ETGs.