A halo model for cosmological Lyman-limit systems

We present an analytical model for cosmological Lyman-limit systems (LLS) that successfully reproduces the observed evolution of the mean free path (λeff) of ionizing photons. The evolution of the co-moving mean free path is predominantly a consequence of the changing meta galactic photoionization rate and the increase with cosmic time of the minimum mass below which haloes lose their gas due to photoheating. In the model, Lyman-limit absorption is caused by highly ionized gas in the outskirt of dark matter haloes. We exploit the association with haloes to compute statistical properties of λeff and of the bias, b, of LLS. The latter increases from b ∼ 1.5 → 2.6 from redshifts z = 2 → 6. Combined with the rapid increase with redshift of the bias of the haloes that host a quasar, the model predicts a rapid drop in the value of λeff when measured in quasar spectra from z = 5 → 6, whereas the actual value of λeff falls more smoothly. We derive an expression for the effective optical depth due to Lyman limit absorption as a function of wavelength and show that it depends sensitively on the poorly constrained number density of LLS as a function of column density. The optical depth drops below unity for all wavelengths below a redshift of ∼2.5 which is therefore the epoch when the Universe first became transparent to ionizing photons

The impact of stellar feedback on galaxies and dark matter halos

In Chapter 2, we study the inner dark matter profiles of galaxies with halo masses between 1e9-1e12Msun and stellar masses between 1e4-1e11Msun in the ``Feedback In Realistic Environment'' (FIRE) cosmological simulations. We find repeated episodes of feedback-driven outflows can transfer energy to DM and flatten the inner DM profiles. kpc-size DM cores form in galaxies with halo masses similar 1e11Msun, since feedback energy is sufficient to reduce inner DM density. At halo mass similar to 1e12 Msun, baryonic infall into halo center can contract DM halos, which effectively cancel the effect from feedback, producing DM profiles close to the Navarro-Frenk-White (NFW) profile.In Chapter 3, we study the formation mechanism of the ultra diffuse galaxies (UDGs) with galaxies with the z=0 stellar masses between 1e4-1e11Msun in the cosmological FIRE simulations. We show dwarf galaxies with stellar mass similar to 1e8 Msun, expanded by stellar feedback, quenched, and then passively evolving in galaxy clusters, can reproduce the properties of ``red'' UDGs. We find if those dwarf galaxies are not quenched, they produce blue diffuse galaxies, which could be prevalent in the field environment. In Chapter 4, we present the first implementation of the cosmic ray (CR) feedback in the FIRE simulation. We study non cosmological simulations of dwarf, dwarf starburst, and Lstar galaxies with CR feedback, including advection, isotropic/anisotropic diffusion, and/or streaming. We constrain CR propagation models by comparing the simulated star formation rate and GeV gamma-ray emission with the observed nearby and starburst galaxies. We find the ``effective'' isotropic diffusion coefficients to be around 3e29cm^2/s to match the observations

Simulations of the reionization of the clumpy intergalactic medium with a novel particle-based two-moment radiative transfer scheme

The progress of cosmic reionization depends on the presence of over-dense regions that act as photon sinks. Such sinks may slow down ionization fronts as compared to a uniform intergalactic medium (IGM) by increasing the clumping factor. We present simulations of reionization in a clumpy IGM resolving even the smallest sinks. The simulations use a novel, spatially adaptive and efficient radiative transfer implementation in the SWIFT SPH code, based on the two-moment method. We find that photon sinks can increase the clumping factor by a factor of ∼10 during the first ∼100 Myrs after the passage of an ionization front. After this time, the clumping factor decreases as the smaller sinks photoevaporate. Altogether, photon sinks increase the number of photons required to reionize the Universe by a factor of η ∼2, as compared to the homogeneous case. The value of η also depends on the emissivity of the ionizing sources

The impact and response of mini-haloes and the interhalo medium on cosmic reionization

An ionization front (I-front) that propagates through an inhomogeneous medium is slowed down by self-shielding and recombination's. We perform cosmological radiation hydrodynamics simulations of the I-front propagation during the epoch of cosmic reionization. The simulations resolve gas in mini-haloes (halo mass 104 ≲ Mh[M⊙] ≲ 108) that could dominate recombination's, in a computational volume that is large enough to sample the abundance of such haloes. The numerical resolution is sufficient (gas-particle mass ∼20 M⊙ and spatial resolution <0.1 ckpc) to allow accurate modelling of the hydrodynamic response of gas to photoheating. We quantify the photoevaporation time of mini-haloes as a function of Mh and its dependence on the photoionization rate, Γ−12, and the redshift of reionization, zi. The recombination rate can be enhanced over that of a uniform medium by a factor ∼10−20 early on. The peak value increases with Γ−12 and decreases with zi, due to the enhanced contribution from mini-haloes. The clumping factor, cr, decreases to a factor of a few at ∼100 Myr after the passage of the I-front when the mini-haloes have been photoevaporated; this asymptotic value depends only weakly on Γ−12. Recombination's increase the required number of photons per baryon to reionize the Universe by 20 per cent–100 per cent, with the higher value occurring when Γ−12 is high and zi is low. We complement the numerical simulations with simple analytical models for the evaporation rate and the inverse Strömgren layer. The study also demonstrates the proficiency and potential of SPH-M1RT to address astrophysical problems in high-resolution cosmological simulations

Reconciling observed and simulated stellar halo masses

We use cosmological hydrodynamical simulations of Milky-Way-mass galaxies from the FIRE project to evaluate various strategies for estimating the mass of a galaxy's stellar halo from deep, integrated-light images. We find good agreement with integrated-light observations if we mimic observational methods to measure the mass of the stellar halo by selecting regions of an image via projected radius relative to the disk scale length or by their surface density in stellar mass . However, these observational methods systematically underestimate the accreted stellar component, defined in our (and most) simulations as the mass of stars formed outside of the host galaxy, by up to a factor of ten, since the accreted component is centrally concentrated and therefore substantially obscured by the galactic disk. Furthermore, these observational methods introduce spurious dependencies of the estimated accreted stellar component on the stellar mass and size of galaxies that can obscure the trends in accreted stellar mass predicted by cosmological simulations, since we find that in our simulations the size and shape of the central galaxy is not strongly correlated with the assembly history of the accreted stellar halo. This effect persists whether galaxies are viewed edge-on or face-on. We show that metallicity or color information may provide a way to more cleanly delineate in observations the regions dominated by accreted stars. Absent additional data, we caution that estimates of the mass of the accreted stellar component from single-band images alone should be taken as lower limits.Comment: Version accepted by Ap

Swift: A modern highly-parallel gravity and smoothed particle hydrodynamics solver for astrophysical and cosmological applications

Numerical simulations have become one of the key tools used by theorists in all the fields of astrophysics and cosmology. The development of modern tools that target the largest existing computing systems and exploit state-of-the-art numerical methods and algorithms is thus crucial. In this paper, we introduce the fully open-source highly-parallel, versatile, and modular coupled hydrodynamics, gravity, cosmology, and galaxy-formation code Swift. The software package exploits hybrid shared- and distributed-memory task-based parallelism, asynchronous communications, and domain-decomposition algorithms based on balancing the workload, rather than the data, to efficiently exploit modern high-performance computing cluster architectures. Gravity is solved for using a fast-multipole-method, optionally coupled to a particle mesh solver in Fourier space to handle periodic volumes. For gas evolution, multiple modern flavours of Smoothed Particle Hydrodynamics are implemented. Swiftalso evolves neutrinos using a state-of-the-art particle-based method. Two complementary networks of sub-grid models for galaxy formation as well as extensions to simulate planetary physics are also released as part of the code. An extensive set of output options, including snapshots, light-cones, power spectra, and a coupling to structure finders are also included. We describe the overall code architecture, summarise the consistency and accuracy tests that were performed, and demonstrate the excellent weak-scaling performance of the code using a representative cosmological hydrodynamical problem with ≈300 billion particles. The code is released to the community alongside extensive documentation for both users and developers, a large selection of example test problems, and a suite of tools to aid in the analysis of large simulations run with Swift

Swift: A modern highly-parallel gravity and smoothed particle hydrodynamics solver for astrophysical and cosmological applications

Numerical simulations have become one of the key tools used by theorists in all the fields of astrophysics and cosmology. The development of modern tools that target the largest existing computing systems and exploit state-of-the-art numerical methods and algorithms is thus crucial. In this paper, we introduce the fully open-source highly-parallel, versatile, and modular coupled hydrodynamics, gravity, cosmology, and galaxy-formation code Swift. The software package exploits hybrid task-based parallelism, asynchronous communications, and domain-decomposition algorithms based on balancing the workload, rather than the data, to efficiently exploit modern high-performance computing cluster architectures. Gravity is solved for using a fast-multipole-method, optionally coupled to a particle mesh solver in Fourier space to handle periodic volumes. For gas evolution, multiple modern flavours of Smoothed Particle Hydrodynamics are implemented. Swift also evolves neutrinos using a state-of-the-art particle-based method. Two complementary networks of sub-grid models for galaxy formation as well as extensions to simulate planetary physics are also released as part of the code. An extensive set of output options, including snapshots, light-cones, power spectra, and a coupling to structure finders are also included. We describe the overall code architecture, summarize the consistency and accuracy tests that were performed, and demonstrate the excellent weak-scaling performance of the code using a representative cosmological hydrodynamical problem with $\approx$$300$ billion particles. The code is released to the community alongside extensive documentation for both users and developers, a large selection of example test problems, and a suite of tools to aid in the analysis of large simulations run with Swift.Comment: 39 pages, 18 figures, submitted to MNRAS. Code, documentation, and examples available at www.swiftsim.co

The impact of stellar feedback on galaxies and dark matter halos

In Chapter 2, we study the inner dark matter profiles of galaxies with halo masses between 1e9-1e12Msun and stellar masses between 1e4-1e11Msun in the ``Feedback In Realistic Environment'' (FIRE) cosmological simulations. We find repeated episodes of feedback-driven outflows can transfer energy to DM and flatten the inner DM profiles. kpc-size DM cores form in galaxies with halo masses similar 1e11Msun, since feedback energy is sufficient to reduce inner DM density. At halo mass similar to 1e12 Msun, baryonic infall into halo center can contract DM halos, which effectively cancel the effect from feedback, producing DM profiles close to the Navarro-Frenk-White (NFW) profile.In Chapter 3, we study the formation mechanism of the ultra diffuse galaxies (UDGs) with galaxies with the z=0 stellar masses between 1e4-1e11Msun in the cosmological FIRE simulations. We show dwarf galaxies with stellar mass similar to 1e8 Msun, expanded by stellar feedback, quenched, and then passively evolving in galaxy clusters, can reproduce the properties of ``red'' UDGs. We find if those dwarf galaxies are not quenched, they produce blue diffuse galaxies, which could be prevalent in the field environment. In Chapter 4, we present the first implementation of the cosmic ray (CR) feedback in the FIRE simulation. We study non cosmological simulations of dwarf, dwarf starburst, and Lstar galaxies with CR feedback, including advection, isotropic/anisotropic diffusion, and/or streaming. We constrain CR propagation models by comparing the simulated star formation rate and GeV gamma-ray emission with the observed nearby and starburst galaxies. We find the ``effective'' isotropic diffusion coefficients to be around 3e29cm^2/s to match the observations

Expression of aquaporin-1 in human peritoneal mesothelial cells and its upregulation by glucose In vitro

Aquaporin (AQP) is a family of water channels that are highly selective for the passage of water and occasionally glycerol. In previous studies, only AQP1 was found in human peritoneal endothelial cells in both control subjects and patients on peritoneal dialysis. As human peritoneal mesothelial cells (HPMC) play an important role in dialysis adequacy and fluid balance in continuous ambulatory peritoneal dialysis patients, this study examined whether AQP1 is present in HPMC. It was found that AQP1 mRNA and protein are present in HPMC constitutively. The localization of AQP1 protein in peritoneal mesothelial cells was confirmed by double immunohistochemical staining of the mesothelial lining of human peritoneal membrane. More important, the expression of AQP1 in HPMC is not constitutive and the transcription and biosynthesis of AQP1 in HPMC is inducible by osmotic agents such as glucose and mannitol. There was significant enhancement of AQP1 biosynthesis upon exposure to glucose in a time- and dose-dependent manner (P < 0.0001). Similar findings were observed in the AQP1 biosynthesis by an endothelial cell line, EA.hy 926. Of particular interest, the upregulation in AQP1 mRNA or biosynthesis in mesothelial cells was always significantly higher than that of endothelial cells when the experiments were conducted under identical settings (P < 0.001). AQP1 expression in HPMC was demonstrated for the first time. Osmotic agents upregulate both mRNA and protein expression of this aquaporin. The role of AQP1 in HPMC in maintaining the ultrafiltration of the peritoneal membrane is potentially of clinical interest.link_to_subscribed_fulltex