The chemical history of star-forming galaxies in nearby clusters

Resumen

The aim of this thesis is to investigate the influence of environment on the chemical history of star-forming galaxies in a sample of local Universe clusters. We have achieved this goal through the study of the fundamental relations between the metallicity of galaxies and their main physical properties, such as stellar mass, luminosity, gas content, star formation activity and structure. In order to carry out this study, we have obtained new optical long-slit spectroscopy of the A2151 cluster with the telescopes INT2.5m and WHT4.2m at the ORM. Additionally an extensive spectroscopic database has been extracted from the SDSS DR8, for a large sample of 781 low-mass star-forming galaxies in the clusters: A1656 (Coma), A1367, A779 A634 as well as in A2147, A2151, A2152 of the Hercules supercluster. We have derived the chemical abundances of the ionized interstellar medium of our sample galaxies, for which we have studied the behavior of the MZR and LZR as a function of their environment. The environment has been quantified as a function of cluster-centric distance and also as a function of the local density of galaxies. Overall, our sample of star-forming galaxies exhibits well defined sequences of stellar mass and metallicity (as parametrized by O/H, and the N/O ratio), following the well known general behavior for star-forming galaxies. Notably outside the cores of more massive clusters, the derived slope of the MZR is in agreement with the predictions of state-of-the-art hydrodynamic models. Besides this global behavior, we have found that dwarf/irregular galaxies populating the densest regions in the A2151 cluster show higher metallicity for their mass and crowd the upper part of the MZR and N/O versus stellar mass relations. Furthermore, low-mass star-forming galaxies located at cluster-centric distances R< R200 in Coma (especially) and A1367, appear preferentially located at the upper side of the derived MZR global relations of O/H and N/O versus mass. This observed enhancement in metallicity appears to be dependent of galaxy stellar mass, being higher for the lower mass bins, thus flattening the MZR slope in the core of these massive clusters. This observed behavior reveals that the imprint of the cluster environment shows up in a mass-dependent way, being both, galaxy mass and cluster mass, relevant parameters. This result suggests the important role that intra-cluster medium properties could play in the chemical evolution of cluster galaxies. A physical scenario has been proposed to explain the metal enhancement of low-mass star-forming galaxies in clusters, in the light of the predictions of recent hydrodynamic simulations for galaxy evolution in clusters. Within this framework, this thesis aims at motivating further efforts in theoretical modelling of chemical evolution in dense environments. Additionally to these main conclusions, in the present thesis we have reached other relevant results. We found that star-forming spiral galaxies in A2151 present oxygen abundances close to solar and shallow oxygen abundance gradients, a result suggesting possible gas infall at their centers. For the N/O ratio, even oversolar values have been obtained for the central parts of some galaxies and a significant spatial variation has been observed. A clear trend was found for the gas-phase metallicity of A2151 galaxies, gradually approaching the stellar metallicity as the latter increases from Zsun/2 to Zsun. The outliers of this trend (less chemically evolved systems with approximately equal gas-phase and stellar metallicity) are identifiable with ``newcomers'' in the cluster environment. An overall positive trend has been found in the gas-phase oxygen abundance versus the mass-weighted stellar age, which becomes more prominent in the case of the N/O ratio. The 2D color g-i and EW(Ha) maps of A2151 cluster have revealed the presence of a filament, mainly of low-mass galaxies, to the North of A2151, that reaches down to the cluster core. The g-i and EW(Ha) maps of A2152 ans A2147 indicate more virialized structures; nonetheless, a filamentary structure dominated by blue low-mass star-forming galaxies has been identified entering in A2147 R200 region from South-East. The LZR and N/O ratio vs. stellar mass relation of the HSC low-mass star-forming galaxies have been found to show an intrinsic dispersion that correlates with galaxy color. In the clusters with available HI measurements we have found that most of the dwarf galaxies with available HI mass are either located outside the cluster core or have been recently accreted to the cluster environment and appear consistent with the predictions of the ``closed box'' model. In the cores of these clusters HI detections are scarce, thus star-forming dwarf galaxies there should have suffered an important ram-pressure stripping. The metal enhancement of star-forming dwarfs in the cluster core has been found to be more important when considering the R200 region of the most massive cluster Coma (Mstar~10^{15} Msun. Despite the general good relation of local galaxy density with cluster-centric distance, this effect appears diluted in terms of local galaxy density, suggesting that the relevant parameter able to affect the chemical evolution of star-forming dwarf galaxies should be the presence of an intra-cluster medium. Finally, for the aims of this thesis we performed a study of the morphological and structural properties of the star-forming galaxies in A2151 cluster. This work allowed a careful spectroscopic follow-up of these galaxies with long-slit spectroscopy. For this specific sample of cluster galaxies we derived galaxy stellar masses using SED fitting on SDSS broadband photometry. The fundamental parameters of the underlying stellar component, such as mean metallicity and age were derived via spectral fitting using the population synthesis code STARLIGHT.