Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

A range of experimental results point to the existence of a massive neutrino. The recent high precision measurements of the cosmic microwave background and the large scale surveys of galaxies can be used to place an upper bound on this mass. In this paper we perform a thorough analysis of all assumptions that go into obtaining a credible limit on $\sum m_{\nu}$. In particular we explore the impact of extending parameter space beyond the current standard cosmological model, the importance of priors and the uncertainties due to biasing in large scale structure. We find that the mass constraints are independent of the choice of parameterization as well as the inclusion of spatial curvature. The results of including the possibility of dark energy and tensors perturbations are shown to depend critically on the data sets used. The difference between an upper bound of 2.2 eV, assuming generic initial conditions, and an upper bound of 0.63 eV, assuming adiabaticity and a galaxy bias of 1, demonstrate the dependence of such a constraint on the assumptions in the analysis.

Abstract:

We report on the science case high level specifications for a wide field spectrograph instrument for an Extremely Large Telescope (ELT) and present possible concepts. Preliminary designs are presented which resort to different instrument concepts: monolithic integral field (IFU), multi-IFU, and a smart tunable filter. This work is part of the activities performed in the work package 'Instrumentation' of the 'ELT Design Study', a programme supported by the European Community, Framework Programme 6.

Abstract:

A self consistent effective field theory of modified gravity has recently been proposed with spontaneous breaking of local Lorentz invariance. The symmetry is broken by a vector field with the wrong-sign mass term and it has been shown to have additional graviton modes and modified dispersion relations. In this paper we study the evolution of a homogeneous and isotropic universe in the presence of such a vector field with a minimum lying along the time-like direction. A plethora of different regimes is identified, such as accelerated expansion, loitering, collapse and tracking.

Abstract:

We investigate the relation between the mass of super-massive black holes (Mbh) in QSOs and the mass of the dark matter halos hosting them (Mdh). We measure the widths of broad emission lines (Mgii lambda 2798, Civ lambda 1549) from QSO composite spectra as a function of redshift. These widths are then used to determine virial black hole mass estimates. We compare our virial black hole mass estimates to dark matter halo masses for QSO hosts derived by Croom et al. (2005) based on measurements of QSO clustering. This enables us to trace the Mbh-Mdh relation over the redshift range z=0.5 to 2.5. We calculate the mean zero-point of the Mbh-Mdh relation to be Mbh=10^(8.4+/-0.2)Msun for an Mdh=10^(12.5)Msun. These data are then compared with several models connecting Mbh and Mdh as well as recent hydrodynamical simulations of galaxy evolution. We note that the flux limited nature of QSO samples can cause a Malmquist-type bias in the measured zero-point of the Mbh-Mdh relation. The magnitude of this bias depends on the scatter in the Mbh-Mdh relation, and we reevaluate the zero-point assuming three published values for this scatter. (abridged)