Field galaxies at intermediate redshift (0.2 < z < 0.8) in the direction of the galaxy cluster LCDCS-S001

Abstract

We present a spectroscopic and photometric analysis for eight field galaxies in the direction of the galaxy cluster LCDCS-S001. The spectra were obtained with the GMOS instrument at the Gemini South Observatory. The objects were selected in an i'-band image and the multiobject spectroscopic observations were centred at 7500 A. For the galaxies ID 440 and ID 461, we have determined redshifts of z = 0.7464 and 0.7465, respectively. For the other six galaxies we have confirmed the previous measurements of redshift. The redshifts of the field galaxies are in the range of 0.2201 < z < 0.7784. We determined the blue and visual luminosities and they are brighter than M B = -18.64. The galaxies ID 180, ID 266 and ID 461 follow the Faber-Jackson relation of the Coma and Virgo early-type galaxies, and therefore do not present a brightening of the B luminosity as observed in galaxies at higher redshifts. The stellar velocity dispersion was measured for five galaxies (ID 146, ID 180, ID 266, ID 428 and ID 440) and estimated to be in the range of 200 < a < 346 km s -1 . Lick indices were measured and used to determine the stellar population properties of the galaxies ID 120 and ID 146, by means of spectral synthesis. The first galaxy, ID 120, presents in its spectrum absorption and emission lines, and we have found that the main contribution in the flux at λ5870 A is of a 0.1-Gyr stellar population of solar metallicity. For ID 146, the dominant flux contribution at λ4200 A is provided by a stellar population of 10 Gyr of subsolar metallicity. From stellar population synthesis, we estimated reddening values of E(B - V) = 0.90 and 0.82 for ID 120 and ID 146, respectively. According to classical diagnostic diagrams the emission lines present in the spectrum of ID 120 indicate that it is a starburst galaxy.