Matias Zaldarriaga

Lyα COOLING EMISSION FROM GALAXY FORMATION

Recent numerical and analytical studies have shown thai galaxies accrete most of their baryons via the cold mode, from streams with temperatures T ~ 10 4 -10 5 K. At these temperatures, the streams should radiate primarily in the Lycc line and have therefore been proposed as a model to power the extended, high-redshift objects known as Lyor blobs, and may also be relevant for powering a range of less luminous Lyor sources. We introduce a new Lyor radiative transfer code, aRT, and calculate the transport of the Lycc emission from cold accretion in cosmological hydrodynamical simulations. In this paper, we describe our methodology, and address physical and numerical issues that arc critical to making accurate predictions for the cooling luminosity, but that have been mostly neglected or treated simplistically so far. In particular, we highlight the importance of self-shielding and of properly treating sub-resolution models in numerical simulations. Most existing simulations do not self-consistcntly incorporate these effects, which can lead to order-of-magnitude errors in the predicted cooling luminosity, Using a combination of post-processing ionizing radiative transfer and re-simulation techniques, we develop an approximation to the consistent evolution of the self-shielded gas. We quantify the dependence of the Lya cooling luminosity on halo mass at ; = 3 for the simplified problem of pure gas accretion embedded in the cosmic radiation background and without feedback, and present radiative transfer results for a particular system. While pure cooling in massive halos (without additional energy input from star formation and active galactic nuclei) is in principle sufficient to produce L a ~ lO^-lO 44 erg s 1 blobs, this requires including energy released in gas of density sufficient to form stars, but which is kept 100% gaseous in our optimistic estimates. Excluding emission from such dense gas yields lower luminosities by up to one to two orders of magnitude at high masses, making it difficult to explain the observed Lya blobs with pure cooling. Resonanl scattering produces diffuse Lya halos, even for centrally concentrated emission, and broad double peaked line profiles. In particular, the emergent line widths are in general not representative of the velocity dispersion within galactic halos and cannot be directly used to infer host halo masses.

Cosmic Microwave Background Observables and Their Cosmological Implications

We show that recent measurements of the power spectrum of cosmic microwave background anisotropies by Boomerang and MAXIMA can be mainly characterized by four observables: the position of the first acoustic peak, l1 = 206 ± 6; the height of the first peak relative to COBE normalization, H1 = 7.6 ± 1.4; the height of the second peak relative to the first, H2 = 0.38 ± 0.04; and the height of the third peak relative to the first, H3 = 0.43 ± 0.07. This phenomenological representation of the measurements complements more detailed likelihood analyses in multidimensional parameter space, clarifying the dependence on prior assumptions and the specific aspects of the data leading to the constraints. We illustrate their use in the flat ΛCDM family of models, where we find Ωmh3.8 > 0.079 (or nearly equivalently, the age of the universe t0 0.019, a matter density Ωmh2 0.85 from the peak heights (95% confidence limit). With the aid of several external constraints, notably nucleosynthesis, the age of the universe, and the cluster abundance and baryon fraction, we construct the allowed region in the (Ωm, h) plane; it points to high h (0.6 < h < 0.9) and moderate Ωm (0.25 < Ωm < 0.6).We show that recent measurements of the power spectrum of cosmic microwave background anisotropies by BOOMERanG and MAXIMA can be characterized by four observables, the position of the first acoustic peak l_1= 206 pm 6, the height of the first peak relative to COBE normalization H_1= 7.6 pm 1.4, the height of the second peak relative to the first H_2 = 0.38 pm 0.04, and the height of the third peak relative to the first H_3 = 0.43 pm 0.07. This phenomenological representation of the measurements complements more detailed likelihood analyses in multidimensional parameter space, clarifying the dependence on prior assumptions and the specific aspects of the data leading to the constraints. We illustrate their use in the flat LCDM family of models, where we find Omega_m h^{3.8} > 0.079 (or nearly equivalently, the age of the universe t_0 0.019, a matter density Omega_m h^2 0.85 from the peak heights (95% CL). With the aid of several external constraints, notably nucleosynthesis, the age of the universe and the cluster abundance and baryon fraction, we construct the allowed region in the (Omega_m,h) plane; it points to high h (0.6< h < 0.9) and moderate Omega_m (0.25 < Omega_m < 0.6).

Cosmological Non-Linearities as an Effective Fluid

The universe is smooth on large scales but very inhomogeneous on small scales. Why is the spacetime on large scales modeled to a good approximation by the Friedmann equations? Are we sure that small-scale non-linearities do not induce a large backreaction? Related to this, what is the effective theory that describes the universe on large scales? In this paper we make progress in addressing these questions. We show that the effective theory for the long-wavelength universe behaves as a viscous fluid coupled to gravity: integrating out short-wavelength perturbations renormalizes the homogeneous background and introduces dissipative dynamics into the evolution of long-wavelength perturbations. The effective fluid has small perturbations and is characterized by a few parameters like an equation of state, a sound speed and a viscosity parameter. These parameters can be matched to numerical simulations or fitted from observations. We find that the backreaction of small-scale non-linearities is very small, being suppressed by the large hierarchy between the scale of non-linearities and the horizon scale. The effective pressure of the fluid is always positive and much too small to significantly affect the background evolution. Moreover, we prove that virialized scales decouple completely from the large-scale dynamics, at all orders in the post-Newtonian expansion. We propose that our effective theory be used to formulate a well-defined and controlled alternative to conventional perturbation theory, and we discuss possible observational applications. Finally, our way of reformulating results in second-order perturbation theory in terms of a long-wavelength effective fluid provides the opportunity to understand non-linear effects in a simple and physically intuitive way.

Power Spectrum Correlations Induced by Nonlinear Clustering

Gravitational clustering is an intrinsically nonlinear process that generates significant non-Gaussian signatures in the density field. We consider how these affect power spectrum determinations from galaxy and weak-lensing surveys. Non-Gaussian effects not only increase the individual error bars compared to the Gaussian case but, most importantly, lead to nontrivial cross-correlations between different band powers, correlating small-scale band powers both among themselves and with those at large scales. We calculate the power-spectrum covariance matrix in nonlinear perturbation theory (weakly nonlinear regime), in the hierarchical model (strongly nonlinear regime), and from numerical simulations in real and redshift space. In particular, we show that the hierarchical Ansatz cannot be strictly valid for the configurations of the trispectrum involved in the calculation of the power-spectrum covariance matrix. We discuss the impact of these results on parameter estimation from power-spectrum measurements and their dependence on the size of the survey and the choice of band powers. We show that the non-Gaussian terms in the covariance matrix become dominant for scales smaller than the nonlinear scale knl ~ 0.2 h-1 Mpc-1, depending somewhat on power normalization. Furthermore, we find that cross-correlations mostly deteriorate the determination of the amplitude of a rescaled power spectrum, whereas its shape is less affected. In weak lensing surveys the projection tends to reduce the importance of non-Gaussian effects. Even so, for background galaxies at redshift z ~ 1, the non-Gaussian contribution rises significantly around l ~ 1000 and could become comparable to the Gaussian terms depending upon the power spectrum normalization and cosmology. The projection has another interesting effect: the ratio between non-Gaussian and Gaussian contributions saturates and can even decrease at small enough angular scales if the power spectrum of the three-dimensional field falls faster than k-2.

Constraints from the Lyα Forest Power Spectrum

We use published measurements of the transmission power spectrum of the Ly? forest to constrain several parameters that describe cosmology and thermal properties of the intergalactic medium (IGM). A six-parameter grid is constructed using particle-mesh dark matter simulations together with scaling relations to make predictions for the gas properties. We fit for all parameters simultaneously and identify several degeneracies. We find that the temperature of the IGM can be well determined from the falloff of the power spectrum at small scales. We find a temperature of around 2 ? 104 K, dependent on the slope of the gas equation of state. We see no evidence for evolution in the IGM temperature. We place constraints on the amplitude of the dark matter fluctuations. However, contrary to previous results, the slope of the dark matter power spectrum is poorly constrained. This is because of uncertainty in the effective Jeans smoothing scale, which depends on the temperature as well as the thermal history of the gas.

Reconstructing projected matter density power spectrum from cosmic microwave background

Gravitational lensing distorts the cosmic microwave background (CMB) anisotropies and imprints a characteristic pattern onto it. The distortions depend on the projected matter density between today and redshift

Towards a refined cosmic concordance model: Joint 11-parameter constraints from the cosmic microwave background and large-scale structure

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Galaxy bias and non-linear structure formation in general relativity

. In this paper we develop a method for a direct reconstruction of the projected matter density from the CMB anisotropies. This reconstruction is obtained by averaging over quadratic combinations of the derivatives of CMB field. We test the method using simulations and show that it can successfully recover projected density profile of a cluster of galaxies if there are measurable anisotropies on scales smaller than the characteristic cluster size. In the absence of sufficient small scale power the reconstructed maps have low signal to noise on individual structures, but can give a positive detection of the power spectrum or when cross correlated with other maps of large scale structure. We develop an analytic method to reconstruct the power spectrum including the effects of noise and beam smoothing. Tests with Monte Carlo simulations show that we can recover the input power spectrum both on large and small scales, provided that we use maps with sufficiently low noise and high angular resolution.

Current Cosmological Constraints from a 10 Parameter Cosmic Microwave Background Analysis

We present a method for calculating large numbers of power spectra

CMBFAST for Spatially Closed Universes

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