The Enrichment History of Baryons in the Universe

We present predictions for the cosmic metal budget in various phases of baryons from redshift z=6-0, taken from a cosmological hydrodynamic simulation that includes a well-constrained model for enriched galactic outflows. We find that substantial amounts of metals are found in every baryonic phase at all epochs, with diffuse intergalactic gas dominating the metal budget at early epochs and stars and halo gas dominating at recent epochs. We provide a full accounting of metals in the context of the missing metals problem at z~2.5, showing that ~40% of the metals are in galaxies, and the remainder is divided between diffuse IGM gas and shocked gas in halos and filamentary structures. Comparisons with available observations of metallicity and metal mass fraction evolution show broad agreement. We predict stars have a mean metallicity of one-tenth solar already at z=6, which increases slowly to one-half solar today, while stars just forming today have typically solar metallicity. Our HI column density-weighted mean metallicity (comparable to Damped Ly-alpha system metallicities) slowly increases from one-tenth to one-third solar from z=6-1, then falls to one-quarter solar at z=0. The global mean metallicity of the universe tracks ~50% higher than that of the diffuse phase down to z~1, and by z=0 it has a value around one-tenth solar. Metals move towards higher densities and temperatures with time, peaking around the mean cosmic density at z=2 and an overdensity of 100 at z=0. We study how carbon and oxygen ions trace the path of metals in phase space, and show that OIII-OVII lines provide the most practical option for constraining intergalactic medium metals at z<2.Comment: 10 pages, MNRAS accepted. Minor changes, Figure 1c fixe

A cortical potential reflecting cardiac function

Emotional trauma and psychological stress can precipitate cardiac arrhythmia and sudden death through arrhythmogenic effects of efferent sympathetic drive. Patients with preexisting heart disease are particularly at risk. Moreover, generation of proarrhythmic activity patterns within cerebral autonomic centers may be amplified by afferent feedback from a dysfunctional myocardium. An electrocortical potential reflecting afferent cardiac information has been described, reflecting individual differences in interoceptive sensitivity (awareness of one's own heartbeats). To inform our understanding of mechanisms underlying arrhythmogenesis, we extended this approach, identifying electrocortical potentials corresponding to the cortical expression of afferent information about the integrity of myocardial function during stress. We measured changes in cardiac response simultaneously with electroencephalography in patients with established ventricular dysfunction. Experimentally induced mental stress enhanced cardiovascular indices of sympathetic activity (systolic blood pressure, heart rate, ventricular ejection fraction, and skin conductance) across all patients. However, the functional response of the myocardium varied; some patients increased, whereas others decreased, cardiac output during stress. Across patients, heartbeat-evoked potential amplitude at left temporal and lateral frontal electrode locations correlated with stress-induced changes in cardiac output, consistent with an afferent cortical representation of myocardial function during stress. Moreover, the amplitude of the heartbeat-evoked potential in the left temporal region reflected the proarrhythmic status of the heart (inhomogeneity of left ventricular repolarization). These observations delineate a cortical representation of cardiac function predictive of proarrhythmic abnormalities in cardiac repolarization. Our findings highlight the dynamic interaction of heart and brain in stress-induced cardiovascular morbidity

When Does the Intergalactic Medium Become Enriched?

We use cosmological hydrodynamic simulations including galactic feedback based on observations of local starbursts to find a self-consistent evolutionary model capable of fitting the observations of the intergalactic metallicity history as traced by C IV between z=6.0->1.5. Our main finding is that despite the relative invariance in the measurement of Omega(C IV) as well as the column density and linewidth distributions over this range, continual feedback from star formation-driven winds are able to reproduce the observations, while an early enrichment scenario where a majority of the metals are injected into the IGM at z>6 is disfavored. The constancy of the C IV observations results from a rising IGM metallicity content balanced by a declining C IV ionization fraction due to a 1) decreasing physical densities, 2) increasing ionization background strength, and 3) metals becoming more shock-heated at lower redshift. Our models predict that ~20x more metals are injected into the IGM between z=6->2 than at z>6. We show that the median C IV absorber at z=2 traces metals injected 1 Gyr earlier indicating that the typical metals traced by C IV are neither from very early times nor from very recent feedback.Comment: 6 pages, 3 figures, to appear in the proceedings of "Chemodynamics: from the First Stars to Local Galaxies", Lyon, France, July 10-14, 200

Non-equilibrium chemistry and cooling in the diffuse interstellar medium - I. Optically thin regime

An accurate treatment of the multiphase interstellar medium (ISM) in hydrodynamic galaxy simulations requires that we follow not only the thermal evolution of the gas, but also the evolution of its chemical state, including its molecular chemistry, without assuming chemical (including ionisation) equilibrium. We present a reaction network that can be used to solve for this thermo-chemical evolution. Our model follows the evolution of all ionisation states of the 11 elements that dominate the cooling rate, along with important molecules such as H2 and CO, and the intermediate molecular species that are involved in their formation (20 molecules in total). We include chemical reactions on dust grains, thermal processes involving dust, cosmic ray ionisation and heating and photochemical reactions. We focus on conditions typical for the diffuse ISM, with densities of 10^-2 cm^-3 < nH < 10^4 cm^-3 and temperatures of 10^2 K < T < 10^4 K, and we consider a range of radiation fields, including no UV radiation. In this paper we consider only gas that is optically thin, while paper II considers gas that becomes shielded from the radiation field. We verify the accuracy of our model by comparing chemical abundances and cooling functions in chemical equilibrium with the photoionisation code Cloudy. We identify the major coolants in diffuse interstellar gas to be CII, SiII and FeII, along with OI and H2 at densities nH > 10^2 cm^-3. Finally, we investigate the impact of non-equilibrium chemistry on the cooling functions of isochorically or isobarically cooling gas. We find that, at T < 10^4 K, recombination lags increase the electron abundance above its equilibrium value at a given temperature, which can enhance the cooling rate by up to two orders of magnitude. The cooling gas also shows lower H2 abundances than in equilibrium, by up to an order of magnitude.Comment: 26 pages, 13 figures, accepted for publication in MNRAS. Corrected an error in figure 2. Supplementary material can be found at http://noneqism.strw.leidenuniv.n

Reionization in Technicolor

We present the Technicolor Dawn simulations, a suite of cosmological radiation-hydrodynamic simulations of the first 1.2 billion years. By modeling a spatially-inhomogeneous UVB on-the-fly with 24 frequencies and resolving dark matter halos down to $10^8 M_\odot$ within 12 $h^{-1}$ Mpc volumes, our simulations unify observations of the intergalactic and circumgalactic media, galaxies, and reionization into a common framework. The only empirically-tuned parameter, the fraction $f_{\mathrm{esc,gal}}(z)$ of ionizing photons that escape the interstellar medium, is adjusted to match observations of the Lyman-$\alpha$ forest and the cosmic microwave background. With this single calibration, our simulations reproduce the history of reionization; the stellar mass-star formation rate relation of galaxies; the number density and metallicity of damped Lyman-$\alpha$ absorbers (DLAs) at $z\sim5$; the abundance of weak metal absorbers; the ultraviolet background (UVB) amplitude; and the Lyman-$\alpha$ flux power spectrum at $z=5.4$. The galaxy stellar mass and UV luminosity functions are underproduced by $\leq2\times$, suggesting an overly vigorous feedback model. The mean transmission in the Lyman-$\alpha$ forest is underproduced at $z<6$, indicating tension between measurements of the UVB amplitude and Lyman-$\alpha$ transmission. The observed SiIV column density distribution is reasonably well-reproduced ($\sim 1\sigma$ low). By contrast, CIV remains significantly underproduced despite being boosted by an intense $>4$ Ryd UVB. Solving this problem by increasing metal yields would overproduce both weak absorbers and DLA metallicities. Instead, the observed strength of high-ionization emission from high-redshift galaxies and absorption from their environments suggest that the ionizing flux from conventional stellar population models is too soft.Comment: 24 pages, 17 figures, accepted to MNRA