Cosmology

The Origin and Evolution of Galaxies and Large Scale Structures

The past decade has witnessed spectacular progress in our empirical exploration of the Universe. WMAP observations and the study of distant supernovae have ushered in a new era of precision cosmology, including discoveries into the geometry of the universe, the kinematics of the Hubble expansion, and the cosmic mass-energy content. However, structure formation continues to be elusive due to inability of measuring key properties of galaxies without large systematic errors and inaccuracies in predicting details about star formation. Cosmology surveys have pushed the most powerful ground- and space-based facilities to their limits to partially reveal the evolution of some types of galaxies; however, a number of fundamental limitations are becoming increasingly clear. due to biases in optical and near-IR based galaxy selection methods and the inability to measure results in spectroscopic redshift for galaxies at redshift z > 6.5. Consequently, a different, complementary approach is needed to obtain the complete picture of cosmic star formation history and galaxy evolution.

Galaxy Clusters

Clusters of galaxies, having nearly reached dynamical equilibrium, offer an impressive laboratory to test models of large scale structure formation and the dependence on environment of galaxy formation and evolution. Historically, mm-wavelength observations of clusters have focused on the redshift-independent brightness of the Sunyaev-Zel'dovich Effect (SZE), but with its high resolution and exquisite surface brightness sensitivity, the LMT offers a fundamentally new observational window into the study of galaxy clusters, groups, and other mass-biased environments. LMT users will map the distribution of the intracluster medium (ICM) with 6-10 times higher angular resolution than previous studies. This will in turn enable us to probe the formation process of clusters. Using the Redshift Search Receiver, LMT users will study starburst galaxies in order to better understand the rates of star formation within galaxy clusters.

szeffect

Left: Preliminary map of the Sunyaev-Zel'dovich effect and sub-millimeter galaxy background in the Bullet Cluster by AzTEC at 1.1 mm wavelength. The bright point source in the East is a background luminous infrared galaxy at z ~ 2.7 being lensed by the cluster potential. Right: AzTEC contours overlaid on the X-ray image of the Bullet Cluster.

The LMT also offers an opportunity to study cooling flows in clusters. It has long been understood that the high density and short cooling time in cluster centers should lead to a cooling flow, unless the cooling flow is shut off by an additional source of energy. LMT users will be able to investigate the nature of cooling flows and possible re-heating mechanisms through detailed mapping of the gas and dust distribution in nearby cooling clusters.

Dark Matter and the Structure of Galaxies

According to current theory of structure formation, the matter content of the universe is dominated by cold dark matter (CDM). Because of gravitational instability, perturbations in the CDM density distribution grow with time and form quasi-static clumps called dark matter halos. Luminous objects, such as galaxies and galaxy clusters, are assumed to form in the gravitational potential wells of CDM halos. Thus, a first step in understanding galaxy distribution in the universe is to understand how CDM halos are distributed in space and how galaxies interact with them.

The properties of the dark halo population can be studied in great detail through numerical simulaions and analytical modeling. One method of exploring CDM halo reaction with galaxies is based the conditional luminosity function model, which links galaxies and dark matter halos by matching the number density and clustering properties of galaxies with those of dark matter halos in the current CDM model. Another method uses galaxy systems identified from large redshift surveys of galaxies.