Kinematics and star formation histories of brightest cluster galaxies

Abstract

Brightest cluster galaxies (BCGs) are the most massive and luminous galaxies in the Universe. In this work we study BCGs at intermediate redshifts (0.3 < z < 0.8) to provide more observational insights on the BCG formation and evolution over a 3.4 billion years period, by analysing their stellar kinematic properties and stellar populations with respect to redshift. Studying BCG properties with redshift is important in order to understand their formation and evolutionary histories, as the details are not yet clear. In this work, we study Brightest cluster galaxies Evolution with AdvACT, MeerKAT and SALT (BEAMS) BCGs that are observed with the Southern African Large Telescope (SALT) using the RSS longslit spectrograph. We identify the BCGs from the long-slit data from visual inspection using finder charts and Dark Energy Survey (DES) imaging. We stack the BCG sample with respect to redshift in order to improve the signal-to-noise (S/N) of our sample to derive their kinematics and stellar population parameters. We use the full-spectrum fitting software, pPXF to derive the kinematics of the sample. We also derive their stellar populations with FIREFLY. We investigate the age-redshift relation of the BEAMS BCGs in order to study their evolution. The age-redshift relation of these BCGs is also compared to a sample of 16 Luminous Red Galaxies (LRGs). In this comparison we find that BCGs tend to have much older ages. If we assume that BCGs are passively evolving systems, their ages can, potentially, be used to constrain the expansion of the Universe. If the luminosity–weighted Single Stellar Population (SSP) equivalent ages represents the ages of the galaxies, these estimated ages can be used to calculate the Hubble parameter H(z) and we can also use the BCG ages to constrain cosmological parameters.