105 research outputs found

    What drives black hole and galaxy growth in the EAGLE simulation?

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    In this thesis we investigate what drives the evolution of actively accreting central supermassive black holes and unusually active strongly star-forming galaxies using the Evolution and Assembly of GaLaxies and their Environments (EAGLE) suite of cosmological hydrodynamical simulations. We find that many of our results are intimately tied to the complex evolutionary pathway taken by the central black holes within the simulation. This evolution can be separated into three distinct phases, each related to the mass of the host dark matter halo. In low mass haloes, stellar feedback dominates by driving an effective outflow and substantially hinders the growth of the central black hole. As haloes become more massive, the stellar feedback loses its efficiency, and the outflow stalls. This gives the first opportunity for the central black hole to grow, which is does so initially at a rapid rate. After this phase of rapid growth, the central black hole then becomes sufficiently massive to regulate the gas inflow onto the halo, resulting in both the star formation of the galaxy and any continued rapid growth of the central black hole to be substantially restricted via the outputted energy of an actively accreting supermassive black hole (referred to as an active galactic nuclei, or AGN). In Chapter 2 we discover that this complex evolutionary behaviour is integral to understanding how the growth rates of galaxies and their black holes are related to each other throughout cosmic time. We use this behaviour to explain why the current observational studies report different relationships between galaxy and black hole growth rates depending on the initial selection method used. Finally, in Chapter 3 we find that the evolutionary state of the black hole is also closely connected with high star formation rates in lower mass galaxies (M1011M_* \lesssim 10^{11}~\Msol, where MM_* is the stellar mass of the galaxy). Such 'starbursting' galaxies are rare, and we argue that they are produced through a culmination of two coinciding events; (1) the galaxy must host an underdeveloped black hole (one that has not yet entered its rapid growth phase), thus ensuring that the galaxy has maintained a gas rich reservoir and contains a low mass black hole; and (2) the galaxy must undergo an interaction to kick-start the starburst process. This tells us that strongly star-forming galaxies are a predominately merger driven population that host undermassive black holes, making them fundamentally distinct from the 'typical' star-forming population

    Cirrhosis of the Liver: A Clinical Study of 100 Cases in Glasgow, 1946-1957

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    The gas fractions of dark matter haloes hosting simulated similar to L-star galaxies are governed by the feedback history of their black holes

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    We examine the origin of scatter in the relationship between the gas fraction and mass of dark matter haloes hosting present-day similar to L-star central galaxies in the EAGLE simulations. The scatter is uncorrelated with the accretion rate of the central galaxy's black hole (BH), but correlates strongly and negatively with the BH's mass, implicating differences in the expulsion of gas by active galactic nucleus feedback, throughout the assembly of the halo, as the main cause of scatter. Haloes whose central galaxies host undermassive BHs also tend to retain a higher gas fraction, and exhibit elevated star formation rates (SFRs). Diversity in the mass of central BHs stems primarily from diversity in the dark matter halo binding energy, as these quantities are strongly and positively correlated at fixed halo mass, such that similar to L-star galaxies hosted by haloes that are more (less) tightly bound develop central BHs that are more (less) massive than is typical for their halo mass. Variations in the halo gas fraction at fixed halo mass are reflected in both the soft X-ray luminosity and thermal Sunyaev-Zel'dovich flux, suggesting that the prediction of a strong coupling between the properties of galaxies and their halo gas fractions can be tested with measurements of these diagnostics for galaxies with diverse SFRs but similar halo masses.Peer reviewe

    Interacting galaxies in the IllustrisTNG simulations - I : Triggered star formation in a cosmological context

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    We use the IllustrisTNG cosmological hydrodynamical simulations to investigate how the specific star formation rates (sSFRs) of massive galaxies (M-* > 10(10) M-circle dot) depend on the distance to their closest companions. We estimate sSFR enhancements by comparing with control samples that are matched in redshift, stellar mass, local density, and isolation, and we restrict our analysis to pairs with stellar mass ratios of 0.1 to 10. At small separations (similar to 15 kpc), the mean sSFR is enhanced by a factor of 2.0 +/- 0.1 in the flagship (110.7Mpc)(3) simulation (TNG100-1). Statistically significant enhancements extend out to 3D separations of 280 kpc in the (302.6Mpc)(3) simulation (TNG300-1). We find similar trends in the EAGLE and Illustris simulations, although their sSFR enhancements are lower than those in TNG100-1 by about a factor of two. Enhancements in IllustrisTNG galaxies are seen throughout the redshift range explored (0Peer reviewe

    Supermassive black holes in cosmological simulations - II : the AGN population and predictions for upcoming X-ray missions

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    In large-scale hydrodynamical cosmological simulations, the fate of massive galaxies is mainly dictated by the modelling of feedback from active galactic nuclei (AGNs). The amount of energy released by AGN feedback is proportional to the mass that has been accreted on to the black holes (BHs), but the exact subgrid modelling of AGN feedback differs in all simulations. While modern simulations reliably produce populations of quiescent massive galaxies at z = 10(45) erg s(-1) (although this is sensitive to AGN variability), and leads to smaller fractions of AGN in massive galaxies than in the observations at zPeer reviewe

    Herpesvirus-Associated Acute Urticaria: An Age Matched Case-Control Study

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    Background Acute and recurrent acute urticaria are often associated with multiple factors including infections and recent data suggest a role for herpesviruses. Objective To test the null hypothesis, that is, there is no association of herpesvirus infections with urticaria. Methods Thirty-seven patients between one month and 15 years of age were age matched to 37 controls who were healthy or had mild acute respiratory infections but without urticaria. Patients and controls were followed for 1 to 6 years. Diagnostic studies included DNA detection by real-time PCR for herpes simplex virus (HSV) types 1 and 2, Epstein-Barr virus (EBV), cytomegalovirus (CMV) and human herpesvirus-6 (HHV-6). Tests for other infections included adenovirus, parvovirus B 19, respiratory syncytial virus, influenza A, Group A streptococci, rotavirus, and parasites. Results Specific infections were diagnosed in 26 of 37 cases and among 9 of 37 control children (P=0.0002). Single or concomitant herpesvirus infections occurred in 24 cases and in 4 controls (65% vs 11 %, p=0.0003). Cases had 10 HHV-6 infections, 8 CMV infections, 5 EBV infections, and 4 HSV-1 infections. Conclusion Herpesvirus infections are associated with acute or recurrent acute urticaria