Most of the luminous matter in the Universe reside in the most massive galaxies, as much as 45% in galaxies with mass greater than 1e11 solar masses. This means that most of the star formation in earlier epochs of the universe resulted in the formation of massive galaxies. Thus understanding the evolution and assembly of these galaxies means understanding the history of the majority of baryons ending up as luminous matter.
Massive galaxies also contain most of the mass locked in black holes in the universe and are often sites of violent activity. They also trace the structure of the universe and the most massive elliptical galaxies are found in abundance only in the densest regions of the universe, the galaxy clusters, where they are key players in determining the physical properties of the intra-cluster medium (ICM).
Despite all these striking facts, the formation and evolution of massive galaxies and their central black holes is still relatively poorly understood.
From the point of view of keeping track of the matter content of the universe this is clearly unsatisfactory. One of the reasons for this is he fact that massive galaxies, while containing the majority of stars in the universe, are few in number and the properties of their active galactic nucleus (AGN) and its influence on the surrounding medium can only be properly studied using multi-wavelength data. Thus the need arises for wide-field multi-wavelength data, which only now is becoming available.
The proposed project will consist of three interconnected studies to significantly further our understanding of massive galaxies: 1) The interaction and transformation of massive galaxies through merging, 2) The AGNs in massive galaxies, both their intrinsic properties and their influence on their host galaxy and surrounding medium, and 3) The influence of the environment of the massive galaxies on their physical properties, with a particular emphasis on galaxy clusters.
We will study the interaction and present-day assembly of massive galaxies by conducting a comprehensive survey of mergers of massive galaxies in the last 2.5 billion years using data from the Sloan Digital Sky Survey (SDSS). This study will lead to the largest sample of galaxy mergers ever assembled. The galaxy spectra will be analyzed to derive physical parameters for the galaxies – especially their recent star formation histories to put observational limits on the time-scales involved in the merging of massive galaxies - a poorly known quantity and crucial to understand the relative importance of different paths of massive galaxy assembly. In the longer term we expect this to be a reference sample for future ALMA follow-up studies to understand mergers in detail.
Mergers of massive galaxies are also thought to fuel super-massive black holes in the centre of the galaxies. The resulting AGN activity in turn influences the surrounding medium and our second strand of investigation aims to further our understanding of this interaction between very small and large scales. This will be a multi-wavelength study basing the study of the nuclear region on a sample of more than 500,000 galaxies from the SDSS that have all been spectrally classified into absorption-line, HII, LINERs, transition and Seyfert galaxies. This will be used to construct optical, radio and black hole mass functions, studying the redshift and volume distribution of the sources, as well as tracing the accretion histories and multi-wavelength evolution of the different AGN subclasses and control samples. On a longer time-scale the study will provide fertile ground for high-resolution observations using ALMA.
To study the interaction between the AGN and their surrounding medium we will focus our attention on those AGN residing in clusters, where the ambient density is higher. Here our study will focus on an appropriate high redshift cluster and a sample of galaxy clusters selected from the SDSS at lower redshift. We will obtain radio observations of these clusters and study the properties of the intra-cluster medium (ICM) and its relationship to the AGN residing in the clusters - for the SDSS clusters utilizing the in-depth study of the AGNs mentioned previously. In the longer term we will use this sample as a starting-point to obtain ALMA observations to determine the age of the last AGN turn-on event, and possibly last merger, through synchrotron emission using ALMA observations.
The third part of our project looks at the interaction of galaxies and clusters at a larger scale far out where the ICM density is lower and aims to understand the transformation of galaxies falling into clusters. We will do this using a multi-wavelength study of individual cluster galaxies and their gas content to understand the physical properties of galaxies in clusters and understand in detail how they acquire their characteristics
27 July 2007
26 July 2010