The cluster of galaxies LCDCS-S001 : basic spectroscopic data and stellar population

Abstract

We present kinematic parameters and stellar population properties of selected galaxies in the high-redshift (z=0.7) galaxy cluster LCDCS-S001, determined by spectroscopic data obtained with the Gemini multi-object spectrograph instrument in the Gemini South Observatory. The objects were selected in an i' -band cluster field image, and multi-object spectroscopic observations centred at 7500 Å were performed for 40 objects. Spectral features were successfully identified for 20 objects, and used to determine the redshift of the cluster. We found that 12 objects are cluster members and estimate a median redshift of 0.709 for this cluster. The relative velocities of the cluster members were used to estimate the projected cluster mass, which was found to be 3.54 × 10 14+2.33 −1.41 Mʘ. Lick and Dn(4000) indices were measured and used to determine the stellar population properties of the galaxies, by means of a spectral synthesis through Bruzual & Charlot evolutive models. We found that the bulk of stellar population for the cluster members has a spectrum compatible with solar metallicity and an age between 3.0 and 7.0 Gyr; with only one exception, the flux contribution of younger (t < - 1.0 Gyr) stars in the spectra does not exceed 25 per cent at 4200 Å. Emission [O II] lines were detected for four galaxies, all of which showing a stronger contribution of young stars compared with other cluster galaxies. The equivalent width of the [O II]λ3727 emission line was compared with Magris, Binette & Bruzual models for HII regions.We found good correspondence between our values and the theoretical predictions for solar metallicity and with star formation time-scales 1.0 < τ < 3.0 Gyr.