The Impact of Galaxy Formation on the Diffuse Background Radiation

The far infrared background is a sink for the hidden aspects of galaxy formation. At optical wavelengths, ellipticals and spheroids are old, even at $z \sim 1.$ Neither the luminous formation phase nor their early evolution is seen in the visible. We infer that ellipticals and, more generally, most spheroids must have formed in dust-shrouded starbursts. In this article, we show how separate tracking of disk and spheroid star formation enables us to infer that disks dominate near the peak in the cosmic star formation rate at z \lapproxeq 2 and in the diffuse ultraviolet/optical/infrared background, whereas spheroid formation dominates the submillimetre background.Comment: 12 pages, 5 figures, to appear in proceedings of IAU symp.204, "The Extragalactic Infrared Background and its Cosmological Implications", Martin Harwit and Michael G. Hauser, ed

Macroeconomic effects of demographic change in an OLG model for a small open economy : the case of Belgium

In the absence of behavioural adjustments, demographic change may cut off about 0.4%- point on average from the annual per capita growth rate in the next 25 years. The behavioural responses of households and firms to declining fertility and rising life expectancy may significantly change this outcome, but the sign and the size of this change are unclear. In this paper we construct and parameterize a large-scale OLG model for a small open economy to quantify (the net effect of) these behavioural adjustments. Important endogenous variables in the model are hours worked and (un)employment, investment in human and physical capital, per capita growth and inequality. Individuals differ not only by age, but also by innate ability. We calibrate the model to Belgium and find that it replicates key data since about 1960 remarkably well. Simulating the model, we observe significant (positive) behavioural adjustments by households and firms, but these do not reverse the negative arithmetical effect of projected future demographic change on per capita growth. Many of the adjustments have already taken place in previous decades. Furthermore, ongoing adjustments do not affect future domestic output due to capital outflow in a small open economy. To counter (very) poor per capita growth in the next two decades, policy changes will be necessary

Galactic star formation in parsec-scale resolution simulations

The interstellar medium (ISM) in galaxies is multiphase and cloudy, with stars forming in the very dense, cold gas found in Giant Molecular Clouds (GMCs). Simulating the evolution of an entire galaxy, however, is a computational problem which covers many orders of magnitude, so many simulations cannot reach densities high enough or temperatures low enough to resolve this multiphase nature. Therefore, the formation of GMCs is not captured and the resulting gas distribution is smooth, contrary to observations. We investigate how star formation (SF) proceeds in simulated galaxies when we obtain parsec-scale resolution and more successfully capture the multiphase ISM. Both major mergers and the accretion of cold gas via filaments are dominant contributors to a galaxy's total stellar budget and we examine SF at high resolution in both of these contexts.Comment: 4 pages, 4 figures. To appear in the proceedings for IAU Symposium 270: Computational Star Formation (eds. Alves, Elmegreen, Girart, Trimble

Galaxy Modelling - II. Multi-Wavelength Faint Counts from a Semi-Analytic Model of Galaxy Formation

(Abridged) This paper predicts self-consistent faint galaxy counts from the UV to the submm wavelength range. The STARDUST spectral energy distributions described in Devriendt et al. (1999) are embedded within the explicit cosmological framework of a simple semi-analytic model of galaxy formation and evolution. We build a class of models which capture the luminosity budget of the universe through faint galaxy counts and redshift distributions in the whole wavelength range spanned by our spectra. In contrast with a rather stable behaviour in the optical and even in the far-IR, the submm counts are dramatically sensitive to variations in the cosmological parameters and changes in the star formation history. Faint submm counts are more easily accommodated within an open universe with a low value of $\Omega_0$, or a flat universe with a non-zero cosmological constant. This study illustrates the implementation of multi-wavelength spectra into a semi-analytic model. In spite of its simplicity, it already provides fair fits of the current data of faint counts, and a physically motivated way of interpolating and extrapolating these data to other wavelengths and fainter flux levels.Comment: 13 pages, 10 figures, to appear in A&

The spectral appearance of primeval galaxies

The current and forthcoming observations of large samples of high-redshift galaxies selected according to various photometric and spectroscopic criteria can be interpreted in the context of galaxy formation, by means of models of evolving spectral energy distributions (SEDs). We hereafter present STARDUST which gives synthetic SEDs from the far UV to the submm wavelength range. These SEDs are designed to be implemented into semi-analytic models of galaxy formation.Comment: 10 pages, Latex, 8 postscript figures, to be published in the Proceedings of the meeting ``Clustering at High Redshift'', ASP Conference Serie

ETEC colonisation factors disrupt the antigen presenting capacity of porcine intestinal dendritic cells

Enterotoxigenic E. coli (ETEC) are not only a major cause of diarrhoea in travellers to and children in developing countries, but also cause neonatal and postweaning diarrhoea in piglets, leading to a reduced feed conversion and a higher mortality rate. As a consequence ETEC infections result in severe economic losses in the swine production industry. This intestinal pathogen displays colonisation factors or fimbriae on its surface enabling the microorganism to adhere to the intestinal epithelium (Fig. 1). In pig, F4 and F18 fimbriae are the most frequently associated with ETEC-induced diarrhoea1. As opposed to F4 fimbriae, oral immunisation with F18 fimbriae doesn’t protect piglets from a subsequent challenge infection2. F18 fimbriae bind glycosphingolipids in the apical membrane of enterocytes, but no transcytosis occurs, resulting in lower sunepithelial antigen concentrations as compared to F4 fimbriae, which bind the transcytotic receptor aminopeptidase N3,4. However, M-cell mediated transport of F18 fimbriae should still occur. Hence, besides a lower antigen concentration, these fimbriae could affect the function of intestinal antigen presenting cells. Here, we investigated the influence of purified F18 fimbriae on the antigen presentation capacity of small intestinal lamina propria dendritic cells (LPDCs)

Zooming in on supermassive black holes: how resolving their gas cloud host renders their accretion episodic

Born in rapidly evolving mini-halos during the first billion years of the Universe, super- massive black holes (SMBH) feed from gas flows spanning many orders of magnitude, from the cosmic web in which they are embedded to their event horizon. As such, accretion onto SMBHs constitutes a formidable challenge to tackle numerically, and currently requires the use of sub-grid models to handle the flow on small, unresolved scales. In this paper, we study the impact of resolution on the accretion pattern of SMBHs initially inserted at the heart of dense galactic gas clouds, using a custom super-Lagrangian refinement scheme to resolve the black hole (BH) gravitational zone of influence. We find that once the self-gravitating gas cloud host is sufficiently well re- solved, accretion onto the BH is driven by the cloud internal structure, independently of the BH seed mass, provided dynamical friction is present during the early stages of cloud collapse. For a pristine gas mix of hydrogen and helium, a slim disc develops around the BH on sub-parsec scales, turning the otherwise chaotic BH accretion duty cycle into an episodic one, with potentially important consequences for BH feedback. In the presence of such a nuclear disc, BH mass growth predominantly occurs when infalling dense clumps trigger disc instabilities, fuelling intense albeit short-lived gas accretion episodes.Comment: Resubmitted to mnras after reviewer comments, 24 page

AGN feedback using AMR cosmological simulations

Feedback processes are thought to solve some of the long-standing issues of the numerical modelling of galaxy formation: over-cooling, low angular momentum, massive blue galaxies, extra-galactic enrichment, etc. The accretion of gas onto super-massive black holes in the centre of massive galaxies can release tremendous amounts of energy to the surrounding medium. We show, with cosmological Adaptive Mesh Refinement simulations, how the growth of black holes is regulated by the feedback from Active Galactic Nuclei using a new dual jet/heating mechanism. We discuss how this large amount of feedback is able to modify the cold baryon content of galaxies, and perturb the properties of the hot plasma in their vicinity.Comment: 4 pages, 2 figures, contribution to the Astronomical Society of the Pacific Conference Series for the Cefal\`u meeting "Advances in computational astrophysics: methods, tools and outcomes

Sparse Regression with Multi-type Regularized Feature Modeling

Within the statistical and machine learning literature, regularization techniques are often used to construct sparse (predictive) models. Most regularization strategies only work for data where all predictors are treated identically, such as Lasso regression for (continuous) predictors treated as linear effects. However, many predictive problems involve different types of predictors and require a tailored regularization term. We propose a multi-type Lasso penalty that acts on the objective function as a sum of subpenalties, one for each type of predictor. As such, we allow for predictor selection and level fusion within a predictor in a data-driven way, simultaneous with the parameter estimation process. We develop a new estimation strategy for convex predictive models with this multi-type penalty. Using the theory of proximal operators, our estimation procedure is computationally efficient, partitioning the overall optimization problem into easier to solve subproblems, specific for each predictor type and its associated penalty. Earlier research applies approximations to non-differentiable penalties to solve the optimization problem. The proposed SMuRF algorithm removes the need for approximations and achieves a higher accuracy and computational efficiency. This is demonstrated with an extensive simulation study and the analysis of a case-study on insurance pricing analytics