What Does Clustering Tell Us About the Buildup of the Red Sequence?

We analyze the clustering of red and blue galaxies from four samples spanning a redshift range of 0.4<z<2.0 to test the various scenarios by which galaxies evolve onto the red sequence. The data are taken from the UKIDSS Ultra Deep Survey, DEEP2, and COMBO-17. The use of clustering allows us to determine what fraction of the red sequence is made up of central galaxies and satellite galaxies. At all redshifts, including z=0, the data are consistent with ~60% of satellite galaxies being red or quenched, implying that ~1/3 of the red sequence is comprised of satellite galaxies. More than three-fourths of red satellite galaxies were moved to the red sequence after they were accreted onto a larger halo. The constant fraction of satellite galaxies that are red yields a quenching time for satellite galaxies that depends on redshift in the same way as halo dynamical times; t_Q ~ (1+z)^{-1.5}. In three of the four samples, the data favor a model in which red central galaxies are a random sample of all central galaxies; there is no preferred halo mass scale at which galaxies make the transition from star-forming to red and dead. The large errors on the fourth sample inhibit any conclusions. Theoretical models in which star formation is quenched above a critical halo mass are excluded by these data. A scenario in which mergers create red central galaxies imparts a weaker correlation between halo mass and central galaxy color, but even the merger scenario creates tension with red galaxy clustering at redshifts above 0.5. These results suggest that the mechanism by which central galaxies become red evolves from z=0.5 to z=0.Comment: 18 emulateapj pages, 13 figures. submitted to Ap

Learning journeys: sharing resources for embedding progressive learning development

Following on from work done on integrating learning development into the curriculum (Hill and Tinker, 2013), we have since concentrated on specific aspects of student progression, and in particular how the ‘forgotten’ second year of study (Tobolowsky, 2008) can be used to bridge the gap between first and final years. Through focus groups with students, staff and learning developers, we have established where perceptions of a multi-layered learning journey merge and diverge. Using voices from the focus groups, this presentation identifies shared themes of progressive learning development, but also illustrates the complexity and conflict inherent in these perceptions. The challenge for learning developers is to acknowledge these tensions and design curricula resources and timely interventions which balance the expectations of both teachers and learners. We will showcase a new website resource, developed with ALDinHE, which provides materials to encourage and support learning developers to collaborate with subject specialists in embedding academic, information literacy and employability skills progressively within the curriculum. These materials include a searchable database of case studies, a bank of research literature, and audio, video and workshop resources. Experiences, ideas and concerns of learning developers, captured at the ALDinHE Embedding Skills Day (June 2012), are also incorporated