Radiative transfer of ionizing radiation through gas and dust: stellar source case

We present a new dust extension to the Monte Carlo radiative transfer code crash, which enables it to simulate the propagation of ionizing radiation through mixtures of gas and dust. The new code is applied to study the impact of dust absorption on idealized galactic H II regions and on small scale reionization. We find that H II regions are reduced in size by the presence of dust, while their inner temperature and ionization structure remain largely unaffected. In the small scale reionization simulation, dust hardens ionization fronts and delays the overlap of ionized bubbles. This effect is found to depend only weakly on the assumed abundance of dust in underdense regions.Comment: 17 pages, 14 figures. Accepted for publication in MNRA

Ionizing photon production and escape fractions during cosmic reionization in the TNG50 simulation

In this work we investigate the dependence of the escape fraction of ionizing photons, $f_{\rm esc}$, on various galaxy and host halo properties during the epoch of reionization. We post-process the TNG50 magneto-hydrodynamical simulation from the IllustrisTNG project using the 3D multi-frequency radiative transfer code CRASH. Our work covers the stellar mass range $10^6 \lesssim M_\star/{\rm M_\odot} \lesssim 10^8$ at redshifts $6 < z < 10$. Adopting an unresolved, cloud-scale escape fraction parameter of unity, the halo escape fraction $f_{\rm esc}$ increases with mass from $\sim 0.3$ at $M_\star = 10^6$M$_\odot$ to $\sim 0.6$ at $M_\star = 10^{7.5}$M$_\odot$, after which we find hints of a turnover and decreasing escape fractions for even more massive galaxies. However, we demonstrate a strong and non-linear dependence of $f_{\rm esc}$ on the adopted sub-grid escape fraction. In addition, $f_{\rm esc}$ has significant scatter at fixed mass, driven by diversity in the ionizing photon rate together with a complex relationship between (stellar) source positions and the underling density distribution. The global emissivity is consistent with observations for reasonable cloud-scale absorption values, and halos with a stellar mass $\lesssim 10^{7.5}$M$_\odot$ contribute the majority of ionizing photons at all redshifts. Incorporating dust reduces $f_{\rm esc}$ by a few percent at $M_\star \lesssim 10^{6.5}$M$_\odot$, and up to 10\% for larger halos. Our multi-frequency approach shows that $f_{\rm esc}$ depends on photon energy, and is reduced substantially at $E>54.4$eV versus lower energies. This suggests that the impact of high energy photons from binary stars is reduced when accounting for an energy dependent escape fraction.Comment: 19 pages, 15 figures, submitted to MNRA

Floquet-engineering topological transitions in a twisted transition metal dichalcogenide homobilayer

Motivated by the recent experimental realization of twisted transition metal dichalcogenide bilayers, we study a simplified model driven by different forms of monochromatic light. As a concrete and representative example we use parameters that correspond to a twisted MoTe$_2$ homobilayer. First, we consider irradiation with circularly polarized light in free space and demonstrate that the corresponding Floquet Hamiltonian takes the same form as the static Hamiltonian, only with a constant overall shift in quasi-energy. This is in stark contrast to twisted bilayer graphene, where new terms are typically generated under an analagous drive. Longitudinal light, on the other hand, which can be generated from the transverse magnetic mode in a waveguide, has a much more dramatic effect--it renormalizes the tunneling strength between the layers, which effectively permits the tuning of the twist angle {\em in-situ}. We find that, by varying the frequency and amplitude of the drive, one can induce a topological transition that cannot be obtained with the traditional form of the Floquet drive in free space. Furthermore, we find that strong drives can have a profound effect on the layer pseudospin texture of the twisted system, which coincides with multiple simultaneous band gap closings in the infinite-frequency limit. Surprisingly, these bandgap closings are not associated with topological transitions. For high but finite drive frequencies near $0.7$eV, the infinite-frequency band crossings become band gap minima of the order of $10^{-6}$ eV or smaller

The physical origins of gas in the circumgalactic medium using observationally-motivated TNG50 mocks

Absorbers in the spectrum of background objects probe the circumgalactic medium (CGM) surrounding galaxies, but its physical properties remain unconstrained. We use the cosmological hydrodynamical simulation TNG50 to statistically trace the origins of HI Ly-$\alpha$ absorbers around galaxies at $z = 0.5$ with stellar masses ranging from 10$^8$ to 10$^{11}$ M$_\odot$. We emulate observational CGM studies by considering all gas within a line of sight velocity range of $\pm 500$ km s$^{-1}$ from the central, to quantitatively assess the impact of other galaxy haloes and overdense gas in the IGM that intersect sightlines. The impact of satellites to the total absorber fraction is most significant at impact parameters $0.5 R_{\rm vir} < b < R_{\rm vir}$ and satellites with masses below typical detection limits ($M_* < 10^8$ M$_\odot$) account for 10 (40) per cent of absorbers that intersect any satellite bound to $10^{10}$ and $10^{11}$ $(10^9)$ M$_\odot$ centrals. After confirming outflows are more dominant along the minor axis, we additionally show that at least 20 per cent of absorbers exhibit no significant radial movement, indicating that absorbers can also trace quasi-static gas. The metallicity of absorbers also depends on the azimuthal angle, but this signal is largely driven by enriched inflowing and quasi-static gas. Our work shows that determining the stellar mass of galaxies at $z_{\rm abs}$ is essential to constrain the physical origin of the gas traced in absorption, which in turn is key to characterising the kinematics and distribution of gas and metals in the CGM.Comment: 23 pages, 13 figures. Accepted for publication in MNRA

Does austerity drive public service innovation? Evidence from shared senior management teams in local government

Shared senior management teams are a recent and radical response to financial austerity. They aim to improve the efficiency of public services without the disruption, controversy and transaction costs associated with full-blown organizational mergers. This paper assesses the adoption of this management innovation by English district councils, identifies enablers and barriers to its effective implementation, offers a preliminary assessment of its impacts, and draws out practical lessons for policy makers

Correction: The Endocytic Adaptor Eps15 Controls Marginal Zone B Cell Numbers.

Eps15 is an endocytic adaptor protein involved in clathrin and non-clathrin mediated endocytosis. In Caenorhabditis elegans and Drosophila melanogaster lack of Eps15 leads to defects in synaptic vesicle recycling and synapse formation. We generated Eps15-KO mice to investigate its function in mammals. Eps15-KO mice are born at the expected Mendelian ratio and are fertile. Using a large-scale phenotype screen covering more than 300 parameters correlated to human disease, we found that Eps15-KO mice did not show any sign of disease or neural deficits. Instead, altered blood parameters pointed to an immunological defect. By competitive bone marrow transplantation we demonstrated that Eps15-KO hematopoietic precursor cells were more efficient than the WT counterparts in repopulating B220⁺ bone marrow cells, CD19⁻ thymocytes and splenic marginal zone (MZ) B cells. Eps15-KO mice showed a 2-fold increase in MZ B cell numbers when compared with controls. Using reverse bone marrow transplantation, we found that Eps15 regulates MZ B cell numbers in a cell autonomous manner. FACS analysis showed that although MZ B cells were increased in Eps15-KO mice, transitional and pre-MZ B cell numbers were unaffected. The increase in MZ B cell numbers in Eps15 KO mice was not dependent on altered BCR signaling or Notch activity. In conclusion, in mammals, the endocytic adaptor protein Eps15 is a regulator of B-cell lymphopoiesis

The BarYon CYCLE Project (ByCycle): Identifying and Localizing MgII Metal Absorbers with Machine Learning

The upcoming ByCycle project on the VISTA/4MOST multi-object spectrograph will offer new prospects of using a massive sample of $\sim 1$ million high spectral resolution ($R$ = 20,000) background quasars to map the circumgalactic metal content of foreground galaxies (observed at $R$ = 4000 - 7000), as traced by metal absorption. Such large surveys require specialized analysis methodologies. In the absence of early data, we instead produce synthetic 4MOST high-resolution fibre quasar spectra. To do so, we use the TNG50 cosmological magnetohydrodynamical simulation, combining photo-ionization post-processing and ray tracing, to capture MgII ($\lambda2796$, $\lambda2803$) absorbers. We then use this sample to train a Convolutional Neural Network (CNN) which searches for, and estimates the redshift of, MgII absorbers within these spectra. For a test sample of quasar spectra with uniformly distributed properties ($\lambda_{\rm{MgII,2796}}$, $\rm{EW}_{\rm{MgII,2796}}^{\rm{rest}} = 0.05 - 5.15$ \AA, $\rm{SNR} = 3 - 50$), the algorithm has a robust classification accuracy of 98.6 per cent and a mean wavelength accuracy of 6.9 \AA. For high signal-to-noise spectra ($\rm{SNR > 20}$), the algorithm robustly detects and localizes MgII absorbers down to equivalent widths of $\rm{EW}_{\rm{MgII,2796}}^{\rm{rest}} = 0.05$ \AA. For the lowest SNR spectra ($\rm{SNR=3}$), the CNN reliably recovers and localizes EW$_{\rm{MgII,2796}}^{\rm{rest}}$ $\geq$ 0.75 \AA\, absorbers. This is more than sufficient for subsequent Voigt profile fitting to characterize the detected MgII absorbers. We make the code publicly available through GitHub. Our work provides a proof-of-concept for future analyses of quasar spectra datasets numbering in the millions, soon to be delivered by the next generation of surveys.Comment: 13 pages, 9 figures, 1 table. Accepted for publication in MNRA

The motivations for the adoption of management innovation by local governments and its performance effects

This article analyses the economic, political and institutional antecedents and performance effects of the adoption of shared Senior Management Teams (SMTs) – a management innovation (MI) that occurs when a team of senior managers oversees two or more public organizations. Findings from statistical analysis of 201 English local governments and interviews with organizational leaders reveal that shared SMTs are adopted to develop organisational capacity in resource‐challenged, politically risk‐averse governments, and in response to coercive and mimetic institutional pressures. Importantly, sharing SMTs may reduce rather than enhance efficiency and effectiveness due to redundancy costs and the political transaction costs associated with diverting resources away from a high‐performing partner to support their lower‐performing counterpart

Cosmic rays and the primordial gas

One of the most outstanding problems in the gravitational collapse scenario of early structure formation is the cooling of primordial gas to allow for small mass objects to form. As the neutral primordial gas is a poor radiator at temperatures (T\le10^4\unit{K}), molecular hydrogen is needed for further cooling down to temperatures (T\sim100\unit{K}). The formation of molecular hydrogen is catalyzed by the presence of free electrons, which could be provided by the ionization due to an early population of cosmic rays. In order to investigate this possibility we developed a code to study the effects of ionizing cosmic rays on the thermal and chemical evolution of primordial gas. We found that cosmic rays can provide enough free electrons needed for the formation of molecular hydrogen, and therefore can increase the cooling ability of such primordial gas under following conditions: A dissociating photon flux with (F<10^{-18}\unit{erg cm^{-2} Hz^{-1} s^{-1}}), initial temperature of the gas (\sim10^{3}\unit{K}), total gas number densities (n\ge1\unit{cm^{-3}}), Cosmic ray sources with (\dot{\epsilon}_{CR}>10^{-33}\unit{erg cm^{-3} s^{-1}}).Comment: 15 pages, 5 figure