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The Parameterized Post-Friedmann Framework for Theories of Modified Gravity: Concepts, Formalism and Examples

(2012)

Authors:

Tessa Baker, Pedro G Ferreira, Constantinos Skordis

The Parameterized Post-Friedmann Framework for Theories of Modified Gravity: Concepts, Formalism and Examples

ArXiv 1209.2117 (2012)

Authors:

Tessa Baker, Pedro G Ferreira, Constantinos Skordis

Abstract:

A unified framework for theories of modified gravity will be an essential tool for interpreting the forthcoming deluge of cosmological data. We present such a formalism, the Parameterized Post-Friedmann framework (PPF), which parameterizes the cosmological perturbation theory of a wide variety of modified gravity models. PPF is able to handle spin-0 degrees of freedom from new scalar, vector and tensor fields, meaning that it is not restricted to simple models based solely on cosmological scalar fields. A direct correspondence is maintained between the parameterization and the underlying space of theories, which allows us to build up a `dictionary' of modified gravity theories and their PPF correspondences. In this paper we describe the construction of the parameterization and demonstrate its use through a number of worked examples relevant to the current literature. We indicate how the formalism will be implemented numerically, so that the dictionary of modified gravity can be pitted against forthcoming observations.

Constraining stellar assembly and AGN feedback at the peak epoch of star formation

Monthly Notices of the Royal Astronomical Society: Letters, Volume 425, Issue 1 (2012)

Authors:

T Kimm, S Kaviraj, J Devriendt, S Cohen, R Windhorst, Y Dubois, A Slyz, N Hathi, RR Jr, R O'Connell, M Dopita, J Silk

Abstract:

We study stellar assembly and feedback from active galactic nuclei (AGN) around the epoch of peak star formation (1

Halo abundances and shear in void models

Physics of the Dark Universe Elsevier 1:1-2 (2012) 24-31

Authors:

David Alonso, J Garc铆a-Bellido, T Haugb酶lle, A Knebe

Abstract:

We study the non-linear gravitational collapse of dark matter into halos through numerical N-body simulations of Lema卯tre鈥揟olman鈥揃ondi void models. We extend the halo mass function formalism to these models in a consistent way. This extension not only compares well with the simulated data at all times and radii, but it also gives interesting clues about the impact of the background shear on the growth of perturbations. Our results give hints about the possibility of constraining the background shear via cluster number counts, which could then give rise to strong constraints on general inhomogeneous models, of any scale.

Lyman-alpha emission properties of simulated galaxies: interstellar medium structure and inclination effects

ArXiv 1208.4781 (2012)

Authors:

Anne Verhamme, Yohan Dubois, Jeremy Blaizot, Thibault Garel, Roland Bacon, Julien Devriendt, Bruno Guiderdoni, Adrianne Slyz

Abstract:

[abridged] Aims. The aim of this paper is to assess the impact of the interstellar medium (ISM) physics on Lyman-alpha (Lya) radiation transfer and to quantify how galaxy orientation with respect to the line of sight alters observational signatures. Methods. We compare the results of Lya radiation transfer calculations through the ISM of a couple of idealized galaxy simulations with different ISM models. Results. First, the small-scale structuration of the ISM plays a determinant role in shaping a galaxys Lya properties.The artificially warm, and hence smooth, ISM of G1 yields an escape fraction of 50 percent at the Lya line center, and produces symmetrical double-peak profiles. On the contrary, in G2, most young stars are embedded in thick star-forming clouds, and the result is a 10 times lower escape fraction. G2 also displays a stronger outflowing velocity field, which favors the escape of red-shifted photons, resulting in an asymmetric Lya line. Second, the Lya properties of G2 strongly depend on the inclination at which it is observed: From edge-on to face-on, the line goes from a double-peak profile with an equivalent width of -5 Angstrom to a 15 times more luminous red-shifted asymmetric line with EW 90 Angstrom. Conclusions. Lya radiation transfer calculations can only lead to realistic properties in simulations where galaxies are resolved into giant molecular clouds, putting these calculations out of reach of current large scale cosmological simulations. Finally, we find inclination effects to be much stronger for Lya photons than for continuum radiation. This could potentially introduce severe biases in the selection function of narrow-band Lya emitter surveys, which could indeed miss a significant fraction of the high-z galaxy population.