Dark-ages Reionization & Galaxy Formation Simulation VIII. Suppressed growth of dark matter halos during the Epoch of Reionization

We investigate how the hydrostatic suppression of baryonic accretion affects the growth rate of dark matter halos during the Epoch of Reionization. By comparing halo properties in a simplistic hydrodynamic simulation in which gas only cools adiabatically, with its collisionless equivalent, we find that halo growth is slowed as hydrostatic forces prevent gas from collapsing. In our simulations, at the high redshifts relevant for reionization (between ${\sim}6$ and ${\sim}11$), halos that host dwarf galaxies ($\lesssim 10^{9} \mathrm{M_\odot}$) can be reduced by up to a factor of 2 in mass due to the hydrostatic pressure of baryons. Consequently, the inclusion of baryonic effects reduces the amplitude of the low mass tail of the halo mass function by factors of 2 to 4. In addition, we find that the fraction of baryons in dark matter halos hosting dwarf galaxies at high redshift never exceeds ${\sim}90\%$ of the cosmic baryon fraction. When implementing baryonic processes, including cooling, star formation, supernova feedback and reionization, the suppression effects become more significant with further reductions of ${\sim}30\%$ to 60\%. Although convergence tests suggest that the suppression may become weaker in higher resolution simulations, this suppressed growth will be important for semi-analytic models of galaxy formation, in which the halo mass inherited from an underlying N-body simulation directly determines galaxy properties. Based on the adiabatic simulation, we provide tables to account for these effects in N-body simulations, and present a modification of the halo mass function along with explanatory analytic calculations.Comment: 17 pages, 11 figures; Updated to match the published version. Two changes in Figures 1 and 3 in order to 1) correct bin sizes of the 10^8 and 10^8.5 Msol bins for NOSN_NOZCOOL_NoRe (was 0.5, should be 0.25); 2) include stellar mass in baryon fraction (was missed in Fig. 3). Quantitative description of Fig. 3 changed slightly in Section 2.2. All other results and conclusions remain unchange

Dark-ages reionization and galaxy formation simulation--VII. The sizes of high-redshift galaxies

We investigate high-redshift galaxy sizes using a semi-analytic model constructed for the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulation project. Our fiducial model, including strong feedback from supernovae and photoionization background, accurately reproduces the evolution of the stellar mass function and UV luminosity function. Using this model, we study the size--luminosity relation of galaxies and find that the effective radius scales with UV luminosity as $R_\mathrm{e}\propto L^{0.25}$ at $z{\sim}5$--$9$. We show that recently discovered very luminous galaxies at $z{\sim}7$ (Bowler et al. 2016) and $z{\sim}11$ (Oesch et al. 2016) lie on our predicted size--luminosity relations. We find that a significant fraction of galaxies at $z>8$ will not be resolved by JWST, but GMT will have the ability to resolve all galaxies in haloes above the atomic cooling limit. We show that our fiducial model successfully reproduces the redshift evolution of average galaxy sizes at $z>5$. We also explore galaxy sizes in models without supernova feedback. The no-supernova feedback models produce galaxy sizes that are smaller than observations. We therefore confirm that supernova feedback plays an important role in determining the size--luminosity relation of galaxies and its redshift evolution during reionization.Comment: 10 pages, 4 figures, Accepted for publication in MNRA

Dark ages reionization & galaxy formation simulation XII: Bubbles at dawn

Direct detection of regions of ionized hydrogen (HII) has been suggested as a promising probe of cosmic reionization. Observing the redshifted 21-cm signal of hydrogen from the epoch of reionization (EoR) is a key scientific driver behind new-generation, low-frequency radio interferometers. We investigate the feasibility of combining low-frequency observations with the Square Kilometre Array and near infra-red survey data of the Wide-Field Infrared Survey Telescope to detect cosmic reionization by imaging HII bubbles surrounding massive galaxies during the cosmic dawn. While individual bubbles will be too small to be detected, we find that by stacking redshifted 21-cm spectra centred on known galaxies, it will be possible to directly detect the EoR at $z \sim 9-12$, and to place qualitative constraints on the evolution of the spin temperature of the intergalactic medium (IGM) at $z \geq 9$. In particular, given a detection of ionized bubbles using this technique, it is possible to determine if the IGM surrounding them is typically in absorption or emission. Determining the globally-averaged neutral fraction of the IGM using this method will prove more difficult due to degeneracy with the average size of HII regions.Comment: 14 pages, 11 figures, 2 tables, published in MNRAS. Updated to match published version. Additional results and comments added from previous version. All other results and conclusions remain unchange

Dark-ages Reionization and Galaxy Formation Simulation - X. The small contribution of quasars to reionization

Motivated by recent measurements of the number density of faint AGN at high redshift, we investigate the contribution of quasars to reionization by tracking the growth of central supermassive black holes in an update of the Meraxes semi-analytic model. The model is calibrated against the observed stellar mass function at $z\sim0.6-7$, the black hole mass function at $z\lesssim0.5$, the global ionizing emissivity at $z\sim2-5$ and the Thomson scattering optical depth. The model reproduces a Magorrian relation in agreement with observations at $z<0.5$ and predicts a decreasing black hole mass towards higher redshifts at fixed total stellar mass. With the implementation of an opening angle of 80 deg for quasar radiation, corresponding to an observable fraction of ${\sim}23.4$ per cent due to obscuration by dust, the model is able to reproduce the observed quasar luminosity function at $z\sim0.6-6$. The stellar light from galaxies hosting faint AGN contributes a significant or dominant fraction of the UV flux. At high redshift, the model is consistent with the bright end quasar luminosity function and suggests that the recent faint $z\sim4$ AGN sample compiled by Giallongo et al. (2015) includes a significant fraction of stellar light. Direct application of this luminosity function to the calculation of AGN ionizing emissivity consequently overestimates the number of ionizing photons produced by quasars by a factor of 3 at $z\sim6$. We conclude that quasars are unlikely to make a significant contribution to reionization.Comment: 21 pages, 12 figures; Updated to match the published version. All results and conclusions remain unchange

Complexity and Autonomy in Bronze Age Europe: Assessing Cultural Developments in Eastern Hungary.

This dissertation develops a general anthropological method for studying ‘middle-range societies’ (which includes ‘tribes,’ ‘chiefdoms,’ and ‘ranked’ societies) and applies it to the Middle Bronze Age archaeological sequence in the Körös basin of eastern Hungary (2150-1400 BC). The theoretical emphasis focuses on eight social dimensions that are both cross-culturally significant and archaeologically observable. These dimensions allow monitoring social change at both the local and regional levels. This facilitates integrating models of social change with archaeological evidence such as storage location, house size, scalar stress at large settlements, the intensity of craft production, and estimates of agricultural yields based on intensive gardening and plough agriculture. Site catchment and settlement pattern analysis is another component of the approach, allowing the possibility of inter-site inequalities or dependencies to be evaluated. This anthropological method is used to assess the orthodox understanding of Bronze Age societies – the Ottomány (Otomani) and Gyulavarsánd cultures – as hierarchical polities with elites controlling the production and distribution of prestige goods and other crafts. In contrast, the evidence from the Körös basin in the published literature and from new systematic collection and excavation indicates a pattern of autonomous villages with no sub-segment controlling metallurgy or subsistence goods. This model may not hold in areas surrounding the basin, however, suggesting organizational forms existed as a heterogeneous mosaic across the Bronze Age landscape of the Carpathian Basin.Ph.D.AnthropologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/75970/1/pduffy_1.pd

Dark-ages Reionization and Galaxy Formation Simulation - XIV. Gas accretion, cooling and star formation in dwarf galaxies at high redshift

We study dwarf galaxy formation at high redshift ($z\ge5$) using a suite of high- resolution, cosmological hydrodynamic simulations and a semi-analytic model (SAM). We focus on gas accretion, cooling and star formation in this work by isolating the relevant process from reionization and supernova feedback, which will be further discussed in a companion paper. We apply the SAM to halo merger trees constructed from a collisionless N-body simulation sharing identical initial conditions to the hydrodynamic suite, and calibrate the free parameters against the stellar mass function predicted by the hydrodynamic simulations at z = 5. By making comparisons of the star formation history and gas components calculated by the two modelling techniques, we find that semi-analytic prescriptions that are commonly adopted in the literature of low-redshift galaxy formation do not accurately represent dwarf galaxy properties in the hydrodynamic simulation at earlier times. We propose 3 modifications to SAMs that will provide more accurate high-redshift simulations. These include 1) the halo mass and baryon fraction which are overestimated by collisionless N-body simulations; 2) the star formation efficiency which follows a different cosmic evolutionary path from the hydrodynamic simulation; and 3) the cooling rate which is not well defined for dwarf galaxies at high redshift. Accurate semi-analytic modelling of dwarf galaxy formation informed by detailed hydrodynamical modelling will facilitate reliable semi-analytic predictions over the large volumes needed for the study of reionization.Comment: 20 pages, 10 figures; Updated to match the published version. All results and conclusions remain unchange

Dark-ages reionization and galaxy formation simulation - IX. Economics of reionizing galaxies

Using a series of high-resolution hydrodynamical simulations we show that during the rapid growth of high-redshift (z > 5) galaxies, reserves of molecular gas are consumed over a time-scale of 300Myr, almost independent of feedback scheme. We find that there exists no such simple relation for the total gas fractions of these galaxies, with little correlation between gas fractions and specific star formation rates. The bottleneck or limiting factor in the growth of early galaxies is in converting infalling gas to cold star-forming gas. Thus, we find that the majority of high redshift dwarf galaxies are effectively in recession, with demand (of star formation) never rising to meet supply (of gas), irrespective of the baryonic feedback physics modelled. We conclude that the basic assumption of self-regulation in galaxies - that they can adjust total gas consumption within a Hubble time - does not apply for the dwarf galaxies thought to be responsible for providing most UV photons to reionize the high redshift Universe. We demonstrate how this rapid molecular time-scale improves agreement between semi-analytic model predictions of the early Universe and observed stellar mass functions.Comment: 17 pages, 27 figures, accepted for publication in MNRAS, minor updates to align with final published versio

Dark-ages reionization & galaxy formation simulation IV: UV luminosity functions of high-redshift galaxies

In this paper we present calculations of the UV luminosity function from the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulations (DRAGONS) project, which combines N-body, semi-analytic and semi-numerical modelling designed to study galaxy formation during the Epoch of Reionization. Using galaxy formation physics including supernova feedback, the model naturally reproduces the UV LFs for high-redshift star-forming galaxies from $z{\sim}5$ through to $z{\sim}10$. We investigate the luminosity--star formation rate (SFR) relation, finding that variable SFR histories of galaxies result in a scatter around the median relation of $0.1$--$0.3$ dex depending on UV luminosity. We find close agreement between the model and observationally derived SFR functions. We use our calculated luminosities to investigate the luminosity function below current detection limits, and the ionizing photon budget for reionization. We predict that the slope of the UV LF remains steep below current detection limits and becomes flat at $M_\mathrm{UV}{\gtrsim}{-14}$. We find that $48$ ($17$) per cent of the total UV flux at $z{\sim}6$ ($10$) has been detected above an observational limit of $M_\mathrm{UV}{\sim}{-17}$, and that galaxies fainter than $M_\mathrm{UV}{\sim}{-17}$ are the main source of ionizing photons for reionization. We investigate the luminosity--stellar mass relation, and find a correlation for galaxies with $M_\mathrm{UV}{<}{-14}$ that has the form $M_*{\propto}10^{-0.47M_\mathrm{UV}}$, in good agreement with observations, but which flattens for fainter galaxies. We determine the luminosity--halo mass relation to be $M_\mathrm{vir}{\propto}10^{-0.35M_\mathrm{UV}}$, finding that galaxies with $M_\mathrm{UV}{=}{-20}$ reside in host dark matter haloes of $10^{11.0\pm 0.1}\mathrm{M_\odot}$ at $z{\sim}6$, and that this mass decreases towards high redshift.Comment: 17 pages, 14 figures, Accepted for publication in MNRA

Dark-ages reionization and galaxy formation simulation XI: Clustering and halo masses of high redshift galaxies

We investigate the clustering properties of Lyman-break galaxies (LBGs) at $z\sim6$ - $8$. Using the semi-analytical model {\scshape Meraxes} constructed as part of the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulation (DRAGONS) project, we predict the angular correlation function (ACF) of LBGs at $z\sim6$ - $8$. Overall, we find that the predicted ACFs are in good agreement with recent measurements at $z\sim 6$ and $z\sim 7.2$ from observations consisting of the Hubble eXtreme Deep Field (XDF), the Hubble Ultra-Deep Field (HUDF) and Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. We confirm the dependence of clustering on luminosity, with more massive dark matter haloes hosting brighter galaxies, remains valid at high redshift. The predicted galaxy bias at fixed luminosity is found to increase with redshift, in agreement with observations. We find that LBGs of magnitude $M_{{\rm AB(1600)}} < -19.4$ at $6\lesssim z \lesssim 8$ reside in dark matter haloes of mean mass $\sim 10^{11.0}$- $10^{11.5} M_{\rm \odot}$, and this dark matter halo mass does not evolve significantly during reionisation.Comment: 14 pages, 10 figures, published in MNRA