Populações estelares e gás ionizado em galáxias esferoidais centrais

Abstract

Central galaxies of dark matter massive halos, usually of spheroidal morphology, have distinct physical properties of non-central spheroidal galaxies with comparable mass. Several studies suggest that, because they are in a privileged halo location, such objects are subject to evolutionary processes distinct from those that operate in non-central galaxies. Such mechanisms, however, are misunderstood, particularly as regards their impact on the development of central galaxies baryonic (gas and star) content. In this work, we investigate the physical characteristics of a sample of central galaxies extracted from the SPIDER catalog in function of both the halo mass and the stellar mass of the galaxy, in order to obtain information that allows us to set up a plausible scenario for the formation and evolution of these galaxies. In order to obtain information about the stellar populations of the studied galaxies, we combine the optical spectra of the SDSS survey in halo mass bins and velocity dispersion and use the STARLIGHT code. The reliability of the results was tested by comparing them with samples of mock spectra with different characteristics. To identify the presence of ionized gas, we measured the equivalent width of Ha by Gaussian fits. We find that the extinction AV , the equivalent width of Ha and the contribution of a power law increase as the halo mass increases and the velocity dispersion of the central galaxy decreases. Mean stellar ages have opposite behavior, becoming lower in these same regimes. Mean stellar metallicity is higher as halo mass and velocity dispersion increase. These relationships, however, are quite sensitive to the basis used in the synthesis of stellar populations. The dependence of the equivalent width of Ha with the masses of the galaxy and the halo is, together with the extinction AV , well described by a scenario in which cold gas deposition in a central galaxy is regulated by competition between feedback of the nuclear activity of the central galaxy and the cooling of the intracluster gas, assuming the Bondi accretion model. Thus, ICM gas cooling must be necessary to describe the stellar formation history of a central galaxy. However, given the low equivalent widths of Ha observed, this mechanism is possibly not dominant.