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Astrophysics Luncheon Seminar

Environmental Effects in a Supercluster at z~0.65: Implications for Future All-sky Cosmological Surveys
Presented by Audrey Galametz
Geneva University

Monday, April 16, 2018
12:00 noon in 169-336

Abstract
The birth of structures relies on the formation of massive clusters through the merger of less massive groups along "filaments". Galaxies reaching clusters undergo transformations compared to isolated systems. It has been challenging however to reach a consensus on how groups and filaments influence galaxy evolution. Superclusters are groups of gravitationally bound clusters and overdensities reaching scales of hundreds of Mpc. With their range of density, they provide insights to study the influence of local density on galaxy evolution. They have routinely been found in the local Universe but only a handful of large-scale structures are known at z > 0.5.

We will first present ClJ021734-0513 at z∼0.65 found in the UKIDSS UDS field. We report on spectroscopic follow-ups that confirmed four clusters and a dozen groups and star-forming overdensities. The structure components are at different formation stages: the clusters have a core dominated by passive galaxies while the remaining structures are a mix of star-forming groups. The presence of quiescent galaxies in the core of the latter shows that "preprocessing" has already happened before the groups fall into their massive neighbors. We performed spectral fitting and derived stellar age estimates to investigate the cluster quiescent population as well as the presence of "poststarburst" galaxies in the structure to investigate the quenching mechanisms at play.

This structure offers a unique insight on what we will be able to achieve when the new generation of all-sky surveys such as Euclid will be available. Given their targeted billions of galaxies, complete spectroscopic follow-ups will be unfeasible and these projects will heavily rely on photometric redshifts of high precision. We will summarize what is currently done within the Euclid consortium to reach such precision and what the pilot analysis of ClJ021734-0513 as told us on what is to be expected from large-scale structure studies.

JPL Contact: Daniel Stern

About the Speaker
Audrey Galametz conducted her PhD thesis at the European Southern Observatory (Garching, DE). She also spent a year of her PhD thesis as a visiting astronomer at JPL, working with Daniel Stern and Peter Eisenhardt. She moved to the Observatory of Rome (IT) for her first postdoctoral fellowship, working for the CANDELS survey team from 2011 to 2013. She then continued her research as a Euclid fellow at the Max-Planck-Institute für Extraterrestrische Physics (MPE, Garching, DE) from 2013 to 2017. During that time, she integrated the Science Data Center Germany of the Euclid Consortium, working as a scientific coordinator for the Euclid pipeline. As of December 2017, she is a scientific advisor for the Euclid Science Data Center in Switzerland, based at Geneva Observatory.


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