Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

We present the size evolution of passively evolving galaxies at z 2 identified in Wide-Field Camera 3 imaging from the Early Release Science program. Our sample was constructed using an analog to the passive BzK galaxy selection criterion, which isolates galaxies with little or no ongoing star formation at z ≳ 1.5. We identify 30 galaxies in 40arcmin2 to H < 25mag. By fitting the 10-band Hubble Space Telescope photometry from 0.22 μm ≲ λobs ≲ 1.6 μm with stellar population synthesis models, we simultaneously determine photometric redshift, stellar mass, and a bevy of other population parameters. Based on the six galaxies with published spectroscopic redshifts, we estimate a typical redshift uncertainty of 0.033(1 + z). We determine effective radii from Sérsic profile fits to the H-band image using an empirical point-spread function. By supplementing our data with published samples, we propose a mass-dependent size evolution model for passively evolving galaxies, where the most massive galaxies (M * 1011 M) undergo the strongest evolution from z 2 to the present. Parameterizing the size evolution as (1 + z)-α, we find a tentative scaling of α (- 0.6 0.7) + (0.9 0.4)log (M */109 M), where the relatively large uncertainties reflect the poor sampling in stellar mass due to the low numbers of high-redshift systems. We discuss the implications of this result for the redshift evolution of the M *-Re relation for red galaxies. © 2012. The American Astronomical Society All rights reserved.

Abstract:

In this paper we consider an extension to Eddington's proposal for the gravitational action. We study tensor perturbations of a homogeneous and isotropic space-time in the Eddington regime, where modifications to Einstein gravity are strong. We find that the tensor mode is linearly unstable deep in the Eddington regime and discuss its cosmological implications.

Abstract:

Providing a theoretical basis for the baryonic Tully-Fisher Relation (BTFR; baryonic mass vs rotational velocity in spiral galaxies) in the LCDM paradigm has proved problematic. Simple calculations suggest too low a slope and too high a scatter, and recent semi-analytic models and numerical galaxy simulations typically fail to reproduce some aspects of the relation. Furthermore, the assumptions underlying one model are often inconsistent with those behind another. This paper aims to develop a rigorous prediction for the BTFR in the context of LCDM, using only a priori expected effects and relations, a minimum of theoretical assumptions, and no free parameters. The robustness of the relation to changes in key galactic parameters will be explored. I adopt a modular approach, taking each of the stand alone galaxy relations necessary for constructing the BTFR from up-to-date numerical simulations of dark halos. These relations -- and their expected scatter -- are used to describe model spirals with a range of masses, resulting in a band in the space of the BTFR that represents the current best guess for the LCDM prediction. Consistent treatment of expected LCDM effects goes a large way towards reconciling the naive slope-3 LCDM prediction with the data, especially in the range 10^9 M_sun < M_bar < 10^11 M_sun. The theoretical BTFR becomes significantly curved at M_bar > 10^11 M_sun, but this is difficult to test observationally due to the scarcity of extremely high mass spirals. Low mass gas-rich galaxies have systematically lower rotational velocity than the LCDM prediction, although the relation used to describe baryon mass fractions must be extrapolated in this regime. The fact that the BTFR slope derived here is significantly greater than in early predictions is a direct consequence of a corresponding increase in the expected sensitivity of baryon mass fraction to total halo mass.