Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

Molecular clouds (MCs) are highly structured and ``turbulent''. Colliding gas streams of atomic hydrogen have been suggested as a possible source of MCs, imprinting the filamentary structure as a consequence of dynamical and thermal instabilities. We present a 2D numerical analysis of MC formation via converging HI flows. Even with modest flow speeds and completely uniform inflows, non-linear density perturbations as possible precursors of MCs arise. Thus, we suggest that MCs are inevitably formed with substantial structure, e.g., strong density and velocity fluctuations, which provide the initial conditions for subsequent gravitational collapse and star formation in a variety of galactic and extragalactic environments.

Abstract:

The very high rates of second generation star formation detected and inferred in high-redshift objects should be accompanied by intense millimetre-wave emission from hot core molecules. We calculate the molecular abundances likely to arise in hot cores associated with massive star formation at high redshift, using several different models of metallicity in the early Universe. If the number of hot cores exceeds that in the Milky Way Galaxy by a factor of at least 1000, then a wide range of molecules in high-redshift hot cores should have detectable emission. It should be possible to distinguish between different models for the production of metals and hence hot core molecules should be useful probes of star formation at high redshift. © 2005 RAS.

Abstract:

We analyse the redshift-space (z-space) distortions of quasi-stellar object (QSO) clustering in the 2-degree field instrument (2dF) QSO Redshift Survey (2QZ). To interpret the z-space correlation function, ξ(σ, π), we require an accurate model for the QSO real-space correlation function, ξ(r). Although a single power-law ξ(r) ξ r-γ model fits the projected correlation function [wp(σ)] at small scales, it implies somewhat too shallow a slope for both wp(σ) and the z-space correlation function, ξ(s), at larger scales (≳20 h-1 Mpc). Motivated by the form for ξ(r) seen in the 2dF Galaxy Redshift Survey (2dFGRS) and in standard A cold dark matter (COM) predictions, we use a double power-law model for ξ(r), which gives a good fit to ξ(s) and w p(σ). The model is parametrized by a slope of γ = 1.45 for 1 < r < 10 h-1 Mpc and γ = 2.30 for 10 < r < 40 h-1 Mpc. As found for the 2dFGRS, the value of β determined from the ratio of ξ(s)/ξ(r) depends sensitively on the form of ξ(r) assumed. With our double power-law form for ξ(r), we measure β(z = 1.4) = 0.32-0.11+0.09. Assuming the same model for ξ(r), we then analyse the z-space distortions in the 2QZ ξ(σ, π) and put constraints on the values of Ωm0 and β(z = 1.4), using an improved version of the method of Hoyle et al. The constraints we derive are Ωm0 = 0.35-0.13+0.19, β(z = 1.4) = 0.50-0.15+0.13 in agreement with our ξ(s)/ξ(r) results at the ∼1σ level. © 2005 RAS.

Abstract:

We address the degree and rapidity of generation of small-scale power over the course of structure formation in cosmologies where the primordial power spectrum is strongly suppressed beyond a given wavenumber. We first summarize the situations where one expects such suppressed power spectra and point out their diversity. We then employ an exponential cut-off, which characterizes warm dark matter (WDM) models, as a template for the shape of the cut-off and focus on damping scales ranging from 106 to 109 h -1 M⊙. Using high-resolution simulations, we show that the suppressed part of the power spectrum is quickly (re)generated and catches up with both the linear and the non-linear evolution of the unsuppressed power spectrum. From z = 2 onwards, a power spectrum with a primordial cut-off at 109 h-1 MŁódź, becomes virtually indistinguishable from an evolved cold dark matter (CDM) power spectrum. An attractor such as that described in Zaldarriaga, Scoccimarro & Hui for power spectra with different spectral indices also emerges in the case of truncated power spectra. Measurements of z ∼ 0 non-linear power spectra at ∼100 h-1 kpc cannot rule out the possibility of linear power spectra damped below ∼109 h-1 M ⊙. Therefore, WDM or scenarios with similar features should be difficult to exclude in this way. © 2005 RAS.