Investigating the structure, star formation and stellar mass of the z = 0.9 supercluster RCS 2319+00

The RCS 2319+00 supercluster is a massive supercluster at z = 0.9 comprising three optically selected, spectroscopically confirmed clusters separated by < 3 Mpc on the plane of the sky. This supercluster is one of a few known examples of the progenitors of present-day massive clusters (10^15 solar masses by z ∼ 0.5). RCS 2319+00 therefore allows us to witness the hierarchical buildup of large-scale structure in the Universe.We present an extensive multiwavelength study carried out on the supercluster field. A spectroscopic campaign resulted in 302 structure members spanning three distinct redshift walls separated by ∼ 65 Mpc. We find evidence of substructure in the supercluster field, with a friends-of-friends (FOF) analysis identifying five infalling groups in addition to the three cluster cores. Various methods are presented to estimate the cluster and group masses, finding cluster masses of ∼ 10^14.5–10^14.9 solar masses and average masses of >10^13 solar masses for the infalling groups. These group masses are in agreement with the halo sizes found to be important in cluster galaxy pre-processing in N -body simulation merger tree studies based on hierarchical formation models.In conjunction with multiwavelength data, we use the spectroscopic members and their FOF associations as isolated, group or core galaxies to investigate the role of both the local and global environment on cluster galaxies' stellar mass and star formation. The z = 0.9 RCS2319+00 supercluster is found to follow the local SFR-density relation, with the star formation primarily located in the lower density, infalling isolated and group regions. We see suggestions of both enhanced star formation activity and star formation quenching over the supercluster field. The densest regions of the groups and isolated outskirt galaxies show hints of enhanced star formation activity. There is evidence of a bimodal distribution in the SFRs with stellar mass: the known main sequence of increasing SFR with increasing stellar mass, and a sub-main sequence population of partially quenched star forming galaxies. The sub-main sequence itself seems to be divided between environment-quenching and mass- quenching effects.We propose that the infalling groups in RCS 2319+00 are in varying stages of pre-processing, with their star formation activity level falling between that of the isolated supercluster galaxies and the less-active, more massive cluster cores. Overall, our results align with the theoretical models that predict galaxy pre-processing in group environments before final accretion onto cluster sized halos.Le super-amas RCS2319+00 est un super-amas massif à z = 0,9 comprenant trois amas sélectionnés optiquement et confirmés par spectroscopie. Ces amas sont séparés par < 3 Mpc dans le plan du ciel. Ce super-amas est l'un des rares exemples connus d'ancêtres d'amas massifs d'aujourd'hui (10^15 masses solaires par z ~ 0.5). RCS 2319+00 nous permet donc d'être témoin de l'accumulation hiérarchique de la structure à grande échelle dans l'Univers.Nous présentons une vaste étude multi-longueurs d'ondes dans le champ du super- amas. Une campagne spectroscopique a donné lieu à 302 membres de la structure étalés sur trois sections de décalage vers le rouge (redshift z) distinctes séparés par ~65 Mpc. Nous trouvons des preuves de structure dans le champ du super-amas, avec une analyse dite “friends-of-friends” (FOF), identifiant cinq groupes retombants vers le coeur en plus des trois noyaux d'amas. Diverses méthodes sont présentées pour estimer les masses des amas et groupes. Nous trouvons des amas de masse ~ 10^14,5 - 10^14,9 masses solaires et de masses moyennes de ~10^13 masses solaires pour les groupes retombants vers le centre. Les masses de ces groupes sont en accord avec la taille du halo jugée importante pour la prétraitement des galaxies d'amas dans les études de simulations n-corps basé sur des modèles de formation hiérarchique.En conjonction avec les données multi-longueurs d'ondes, nous utilisons les membres spectroscopiques et leurs associations FOF comme des groupes ou noyaux de galaxies isolé pour étudier le rôle de l'environnement local et global sur la masse stellaire des galaxies de l'amas et leur taux de formation stellaire (SFR). Le super-amas RCS 2319+00 à z = 0,9 suit la relation locale SFR-densité, avec la formation d'étoiles principalement située dans les régions de plus faible densité, celle des galaxies isolées ou en groupe retombant vers le centre. Nous voyons des indications d'activité augmentée de formation stellaire et d'extinction de formation stellaire tous les deux dans le champ du super-amas. Les régions les plus denses des groupes et des galaxies isolées en périphérie de l'amas révèlent des notes d'augmentation de l'activité de formation stellaire. Il existe des preuves d'une distribution bimodale dans la relation de formation stellaire avec la masse stellaire: la séquence principale d'augmentation de la formation stellaire quand la masse stellaire augmente, et une population de séquence sous-principale des galaxies qui ont leur formation stellaire partiellement étouffée. La séquence sous-principale elle-même semble étre divisée entre les effets d'extinction de l'environnement et de masse.Nous proposons que les groupes retombant vers le centre dans RCS 2319+00 sont à divers stades de pré-traitement, avec leur niveau de formation stellaire se situant entre celui des galaxies isolées et celui des noyau plus massives mais moins actifs des amas. Dans l'ensemble, nos résultats sont en accord avec les modèles théoriques qui prédisent le pré-traitement des galaxies dans les environnements de groupe avant l'accrétion finale sur les halos de taille des amas

A spectroscopic survey of the supercluster RCS2319+00 /

This thesis presents the results of a spectroscopic survey of the RCS2319+00 supercluster field using the VIMOS instrument on the 8-meter Very Large Telescope. This system is a rare and massive high-redshift structure, comprising at least three galaxy clusters at z = 0.9, separated by less than 3 Mpc, and is one of the few examples of the progenitors of present-day massive galaxy clusters.We measure 638 new redshifts from a sample of 1134 target sources, 49 of which are consistent with the supercluster redshift. Redshifts are also obtained for 24 radio galaxies within the field, with 6 of these identified as cluster members. We combine the VIMOS redshift catalogue with the data analyzed by Gilbank et al. (2008) from the IMACS spectrograph on the 6-meter Magellan telescope for a total of 1051 redshifts over an area of &sim; 30 x 30 square arcminutes, with 94 spectroscopically confirmed supercluster members. From this combined data set the mean spectroscopic redshifts of the three galaxy clusters were refined and found to be zspec = 0.9056, 0.9041, and 0.9047 for clusters A, B, and C respectively. A new velocity dispersion of sigmav = (1300 +/- 410) km S-1 was calculated for the largest component cluster, A, and was used to estimate a new cluster membership redshift range of 0.8857 &le; z &le; 0.9239.These data will facilitate further scientific study of RCS2319+00 and will shed light on the evolution of massive clusters, hierarchical structure formation, and galaxy evolution. In combination with other spectroscopy this data will allow: the full extent of the supercluster and its substructure in redshift space to be traced; a determination of the dynamical masses of the individual sub-clusters; and a study of the galaxy population within the structure, in particular the star-forming galaxies and active galactic nuclei as traced by radio and infrared emission

The evolution of dusty star formation in galaxy clusters to z = 1 : Spitzer infrared observations of the first red-sequence cluster survey

copyright American Astronomical SocietyWe present the results of an infrared (IR) study of high-redshift galaxy clusters with the MIPS camera on board the Spitzer Space Telescope. We have assembled a sample of 42 clusters from the Red-Sequence Cluster Survey-1 over the redshift range 0.3 <z <1.0 and spanning an approximate range in mass of 10 M. We statistically measure the number of IR-luminous galaxies in clusters above a fixed inferred IR luminosity of 2 × 10 M, assuming a star forming galaxy template, per unit cluster mass and find it increases to higher redshift. Fitting a simple power-law we measure evolution of (1 + z) over the range 0.3 <z <1.0. These results are tied to the adoption of a single star forming galaxy template; the presence of active galactic nuclei, and an evolution in their relative contribution to the mid-IR galaxy emission, will alter the overall number counts per cluster and their rate of evolution. Under the star formation assumption we infer the approximate total star formation rate per unit cluster mass (ΣSFR/ M cluster). The evolution is similar, with ΣSFR/ M cluster ∼ (1 + z). We show that this can be accounted for by the evolution of the IR-bright field population over the same redshift range; that is, the evolution can be attributed entirely to the change in the in-falling field galaxy population. We show that the ΣSFR/ Mcluster (binned over all redshift) decreases with increasing cluster mass with a slope (ΣSFR/) consistent with the dependence of the stellar-to-total mass per unit cluster mass seen locally. The inferred star formation seen here could produce ∼5%-10% of the total stellar mass in massive clusters at z = 0, but we cannot constrain the descendant population, nor how rapidly the star-formation must shut-down once the galaxies have entered the cluster environment. Finally, we show a clear decrease in the number of IR-bright galaxies per unit optical galaxy in the cluster cores, confirming star formation continues to avoid the highest density regions of the universe at z ∼ 0.75 (the average redshift of the high-redshift clusters). While several previous studies appear to show enhanced star formation in high-redshift clusters relative to the field we note that these papers have not accounted for the overall increase in galaxy or dark matter density at the location of clusters. Once this is done, clusters at z ∼ 0.75 have the same or less star formation per unit mass or galaxy as the field.Peer reviewe