Ida Vægter Rasmussen's MSc defense

Title: Gravitational redshift in galaxy clusters with photometric surveys

Supervisors:
Jens Hjorth, DARK
Radoslaw Wojtak, Kavli Institute for Particle Astrophysics and Cosmology, Stanford University

Censor: Steen Hannestad, Aarhus University

Abstract: I will investigate whether it is possible to detect gravitational redshift in galaxy clusters using photometric data, and if this is possible with the Large Synoptic Survey Telescope (LSST). This is done by using simulated data representing different types of spectroscopic and photometric data for galaxy clusters with a mass above 10¹⁴ M_sun h^-1. The three datasets analysed represent: (1) spectroscopic data for all galaxies, (2) spectroscopic data for the Brightest Cluster Galaxies (BCG) and photometric data for all other galaxies, and (3) photometric data for all galaxies, including the BCGs.

The analysis of the spectroscopic data (1) show a clear gravitational redshift signal in clusters, and it is traced out to a radius of 6 Mpc with an average error of ±0.8 km/s. With regards to the photometric data, (2) and (3), the results are less conclusive, as these datasets show a large scatter. The average error in the gravitational redshift for the photometric datasets are ±3.5 km/s and ±5.4 km/s respectively. The analysis was carried out with a sample of 9.1 * 10⁶ galaxies distributed over 6 * 10⁴ clusters.

The LSST is expected to observed 10⁵ clusters, which would make it possible to obtain a total of 1-2 * 10⁷ galaxies from these. Based on extrapolations performed, this would make it possible to bring the error on the gravitational redshift down to ±3 km/s for the photometric datasets, (2) and (3), making it possible to detect gravitational redshift with photometry.

Link to thesis ––>> here