Observational Tests for Competing Theories of Galaxy Formation and the Nature of Dark Matter

Dr Lim, Jeremy Jin Leong   (Principal Investigator (PI))

Dr Coe Dan   (Co-Investigator)

Dr Diego Jose M.   (Co-Investigator)

Mr Lam Daniel   (Co-Investigator)

Dr Umetsu Keiichi   (Co-Investigator)

Dr Zitrin Adi   (Co-Investigator)

Dr Benítez Narciso   (Co-Investigator)

Professor Broadhurst Tom   (Co-Investigator)

Professor Bouwens Rychard J   (Co-Investigator)

36

2016-09-01

540824

Observational Tests for Competing Theories of Galaxy Formation and the Nature of Dark Matter

Dark Matter, Galaxies and Galaxy clusters, Galaxy Formation, Gravitational Lensing, High Redshifts

Physics,Others - Physical Sciences

Physical Sciences (P)

17319316

General Research Fund (GRF)

2016

Completed

1 Robust Lens Models for Galaxy Clusters: The most massive galaxy clusters, like the majority in HFF, are likely to comprise mergers between two galaxy clusters. Our team has developed a unique hybrid scheme to model lensing by galaxy clusters that includes cluster member galaxies but which makes no assumptions about the distribution of matter on larger spatial scales. Referred to as WSLAP+, this method is therefore well suited to the complexity of the massive merging clusters chosen for HFF. This scheme requires a relatively high surface density of multiply-lensed images for generating high-resolution mass maps, a condition best met by the exceptional depth of HFF. Using WSLAP+, we have constructed a rigorous lens model for Abell 2744, the first HFF cluster completed. For the first time ever, we showed that the relative apparent magnitudes of the multiply-lensed images predicted by our lens model are in excellent agreement with their observed apparent magnitudes. With this reliable correction for lensing, we are able to obtain the intrinsic properties of all the lensed galaxies, including those more weakly lensed and do not produce multiple images. The lensed galaxies reach typically 2–3 magnitudes fainter than those found in the deepest blind-field surveys, and provide the crucial leverage for distinguishing between competing theories for galaxy formation that incorporate different forms of dark matter. We also plan to construct robust lens models for the most powerful lensing clusters in the Cluster Lensing And Supernova survey with Hubble (CLASH) program, the predecessor to HFF. By combining results from both CLASH and HFF in our studies, we will be able to take full advantage of the best cluster lensing data currently available. 2 Intrinsic Properties of Multiply-Lensed Sources: With robust lens models in hand, we can maximize the effectiveness of finding multiply-lensed images belonging to the same galaxy by accurately predicting the positions of their counter-images. We also can securely identify each set of lensed images belonging to a given source, derive the geometric redshifts of all the multiply-lensed sources to check against their photometric redshifts (sometimes ambiguous for, especially, galaxies at very high redshifts), and reliably derive their intrinsic properties (luminosity and size). Finally, we can accurately reconstruct the delensed images of well-resolved sources to study their morphology. 3 Galaxy Luminosity and Size Functions: With knowledge of the intrinsic properties of the lensed galaxies, we can then compute the luminosity and size functions of galaxies. More practically, we can derive their luminosity and size distributions – the number of galaxies as a function of luminosity or size over a given field. To derive these distributions, we have developed algorithms to correct for the varying magnification over the cluster and hence the different surface areas at different redshifts probed at different source locations. By comparing the measured luminosity and size distributions against those predicted by theory, we will test competing theories for galaxy formation that incorporate different forms of dark matter. Specifically, we demonstrate that, from the HFF cluster fields, we can address whether the galaxy space density increases with decreasing luminosity as might be expected if DM is cold and collisionless, or whether there is an abrupt decrease (turnover) at a particular luminosity indicative of a lower limiting mass for DM halos imposed by its wavelike nature.