Galaxy chemical evolution is connected with the SFH and the process of interchange of gas between a galaxy and its environment. Both these factors can be aected by the cluster environment as we have seen in Sections 1.2.1 and 1.2.2. The question that we propose to answer in the present thesis is how these eects could leave their imprint on the metal content of galaxies and on the chemical evolution of cluster galaxies. Important questions still remain open regarding the inuence of the environment on the chemical evolution of galaxies, particularly its eect on the scatter of the MZR, and the relative importance of cluster membership vs. local galaxy density. Figuring out the responsible mechanism(s) of the intrinsic scatter of the MZR would help constrain the physical processes driving this relation and subsequently elucidate galaxy evolution scenarios.
To this goal we derive ISM chemical abundances for cluster SF galaxies, and study their relation with the environment (e.g. galaxy cluster-centric distance and local galaxy density) and with fundamental galaxy properties (e.g. galaxy stellar
1.4. The scope of this thesis 17
Figure 1.13: The MZR (up) for 25 nearby dIrr and the residuals in oxygen abundance from the t to the MZR (down). Accurate stellar masses have been derived using IR Spitzer photometry and most of the oxygen abundances estimates are calculated using the direct method (Figure 8,Lee et al. 2006).
mass, luminosity, gas content). We study a sample of northern-hemisphere Abell clusters (Abell 1656, Abell 1367, Abell 779, Abell 634) at a distance of ∼100 Mpc, and the Hercules Supercluster (that includes: Abell 2151, Abell 2152, and Abell 2147) at ∼160 Mpc. This sample of clusters spans a variety of physical properties (such as mass, X-ray luminosity, and evolutionary state), permitting to study the impact on the SFH and the chemical evolution of SF galaxies in a wide range of dierent environments and at large-scale structures.
In the central part of Abell 2151 (the Hercules cluster) we have performed new observations of long-slit spectroscopy, considered in Chapter 3. This new spatially resolved spectroscopy has been used to test the metallicity gradients for Abell 2151 SF galaxies. In Chapter 4 we study a region of 22.5 deg2 around the Hercules Supercluster, and we investigate the distribution of star formation activity and the metal content of galaxies in large scales. Finally, focusing our attention in the low- mass SF population, in Chapter 5 we study the relatively closer-by clusters Abell 1656 (Coma), Abell 1367, Abell 779, and Abell 634.
Overall, the physical mechanisms/processes giving rise to the observed behaviors are discussed on the light of the predictions of recent hydrodynamic models of galaxy
18 Chapter 1. Introduction evolution in dense environments. The results of such an investigation are expected to constrain both the environmental mechanisms that aect cluster galaxies and the the physical processes that govern galaxy evolution, as well as provide new tests for chemical evolution models.
Chapter 2
The sample of clusters
Contents
2.1 Denition of the sample . . . . 19 2.2 Cluster properties . . . . 21 2.3 Hαimaging surveys of our sample clusters . . . . 30
2.1 Denition of the sample
The starting point of this thesis has been the previous deep Hα imaging surveys performed by our group, in a sample of nearby (z∼0.02−0.04) clusters visible from the northern hemisphere (δ&−25 deg). Thus, this work is part of a bigger project which intends creating a census of a well dened sample of emission-line cluster galaxies, for which spectroscopic information as well as integrated Hα luminosities andEW(Hα) will be available. This information permits deriving total galaxy SFRs from the Hα ux, avoiding slit and ber aperture eects. The environmental eects on the chemical evolution of this new sample of cluster galaxies can therefore be considered in relation with the eects on their SFH.
Iglesias-Páramo et al.(2002) presented a deep Hαimaging survey of the central regions of the two nearby clusters Coma (Abell 1656) and Abell 1367, taken with the Wide Field Camera (WFC) at the Isaac Newton Telescope INT2.5m. Reverte (2008) complemented this survey with WFC, observing 5 more Abell clusters: Abell 779, Abell 634, Abell 400, Abell 539, and Abell 2666. In total, these seven clusters fulll the criteria: (1) to be visible from the northern hemisphere and (2) to be located at the same distance at ∼100Mpc (0.02 < z <0.03), belonging thus to a semi-spherical shell of the local Universe.
Additionally, moving to a distance of ∼ 160Mpc, there is the Hercules Super- cluster formed by Abell 2151 (the Hercules cluster), Abell 2147, and Abell 2152.
Cedrés et al.(2009) presented a deep Hαsurvey of the central region of Abell 2151, using the William Herschel Telescope WHT4.2m and the Nordic Optical Telescope NOT2.5m. In the Hercules Supercluster region, a eld of 2 deg2 has been recently observed in Hα by our group, using WFC at INT2.5m and the results will be pre- sented in a forthcoming publication. Figure 2.1is an illustration of the large-scale structures in the local Universe, where are included all the clusters of our sample.
20 Chapter 2. The sample of clusters
Figure 2.1: Illustration of the large-scale structures in the local Universe, including the clusters considered in the present work.
The sample of clusters of this thesis consists of the Abell clusters observed by our group in Hα, that additionally have SDSS spectroscopy: Abell 1656 (Coma cluster), Abell 1367, Abell 779, Abell 634, and the Hercules Supercluster that includes: Abell 2151 (Hercules cluster), Abell 2152, and Abell 2147. Table 2.1 summarizes the properties of our cluster sample. In Column 1 we give the name of the Abell catalog (Abell et al. 1989, from now on we use the abbreviated version for the cluster names, e.g. A1656 stands for Abell 1656), in column 2 and 3 we give the coordinates R.A. and declination in J2000.0 as given in NED, in column 4 the mean cluster redshift as given in NED. The area considered for each cluster is given in degrees projected in the sky (column 5), and in Mpc considering the distance of each cluster (column 6). We have searched for galaxies with SDSS spectroscopy in the indicated regions, and in column 7 we give the total number of galaxies found in the surveyed areas and within the redshift range considered for each cluster (this is our basic spectroscopic galaxy sample for each cluster; concerning the galaxy sample selection we give further details in Chapters 4 and 5).
Table2.1columns 8, 9, and 10 we give the clusterR200, cluster mass and X-ray
2.2. Cluster properties 21