220 research outputs found
The effect of non-equilibrium metal cooling on the interstellar medium
No full textBy using a novel interface between the modern smoothed particle hydrodynamics code GASOLINE2 and the chemistry package KROME, we follow the hydrodynamical and chemical evolution of an isolated galaxy. In order to assess the relevance of different physical parameters and prescriptions, we constructed a suite of 10 simulations, in which we vary the chemical network (primordial and metal species), how metal cooling is modelled (non-equilibrium versus equilibrium; optically thin versus thick approximation), the initial gas metallicity (from 10 to 100 per cent solar), and how molecular hydrogen forms on dust. This is the first work in which metal injection from supernovae, turbulent metal diffusion, and a metal network with non-equilibrium metal cooling are self-consistently included in a galaxy simulation. We find that properly modelling the chemical evolution of several metal species and the corresponding non-equilibrium metal cooling has important effects on the thermodynamics of the gas, the chemical abundances, and the appearance of the galaxy: the gas is typically warmer, has a larger molecular-gas mass fraction, and has a smoother disc. We also conclude that, at relatively high metallicity, the choice of molecular-hydrogen formation rates on dust is not crucial. Moreover, we confirm that a higher initial metallicity produces a colder gas and a larger fraction of molecular gas, with the low-metallicity simulation best matching the observed molecular Kennicutt-Schmidt relation. Finally, our simulations agree quite well with observations that link star formation rate to metal emission lines
The natural emergence of the correlation between H2 and star formation rate surface densities in galaxy simulations
No full textIn this study, we present a suite of high-resolution numerical simulations of an isolated galaxy to test a sub-grid framework to consistently follow the formation and dissociation of H2 with non-equilibrium chemistry. The latter is solved via the package KROME, coupled to the meshless hydrodynamic code GIZMO. We include the effect of star formation (SF), modelled with a physically motivated prescription independent of H2, supernova feedback and mass-losses from low-mass stars, extragalactic and local stellar radiation, and dust and H2 shielding, to investigate the emergence of the observed correlation betweenH2 and SF rate surface densities. We present two different sub-grid models and compare them with on-the-fly radiative transfer (RT) calculations, to assess the main differences and limits of the different approaches. We also discuss a sub-grid clumping factor model to enhance the H2 formation, consistent with our SF prescription, which is crucial, at the achieved resolution, to reproduce the correlation with H2. We find that both sub-grid models perform very well relative to the RT simulation, giving comparable results, with moderate differences, but at much lower computational cost. We also find that, while the Kennicutt-Schmidt relation for the total gas is not strongly affected by the different ingredients included in the simulations, the H2-based counterpart is much more sensitive, because of the crucial role played by the dissociating radiative flux and the gas shielding
Bar resilience to flybys in a cosmological framework
No full textIt has been proposed that close interactions with satellite galaxies can significantly perturb the morphology of the main galaxy. However, the dynamics of an already formed bar following the interaction with the external environment has not been studied in detail in a fully cosmological context. In this work, analysing the cosmological zoom-in simulation Eris2k, we study the effects that a very unequal-mass flyby crossing the stellar disc has on the stability of the pre-existing bar. We characterize the evolution of the bar strength and length showing that the perturbation exerted by the flyby shuffles the orbits of stars for less than one Gyr. After this time, the bar shows a remarkable resilience, reforming with properties comparable to those it had before the interaction. Our work shows that close unequal-mass encounters, the most frequent interactions occurring during the evolution of cosmic structures, have (i) an overall minor impact on the global evolution of the bar in the long term, still (ii) the effect is destructive, and (iii) a very weak interaction is sufficient to dismantle a strong bar leading to its "apparent death". As a consequence, due to the non-negligible duration of the bar-less period, a fraction of observed spiral galaxies classified as non-barred could be prone to bar formation
Light, medium-weight or heavy? The nature of the first supermassive black hole seeds
No full textObservations of hyper-luminous quasars at z>6 reveal the rapid growth of supermassive black holes (SMBHs >10^9 m M_{odot}) whose origin is still difficult to explain. Their progenitors may have formed as remnants of massive, metal free stars (light seeds), via stellar collisions (medium-weight seeds) and/or massive gas clouds direct collapse (heavy seeds). In this work we investigate for the first time the relative role of these three seed populations in the formation of z>6 SMBHs within an Eddington-limited gas accretion scenario. To this aim, we implement in our semi-analytical data-constrained model a statistical description of the spatial fluctuations of Lyman-Werner (LW) photo-dissociating radiation and of metal/dust enrichment. This allows us to set the physical conditions for BH seeds formation, exploring their relative birth rate in a highly biased region of the Universe at z>6. We find that the inclusion of medium-weight seeds does not qualitatively change the growth history of the first SMBHs: although less massive seeds (<10^3 m M_odot) form at a higher rate, the mass growth of a SMBH at z<15 is driven by efficient gas accretion (at a sub-Eddington rate) onto its heavy progenitors (). This conclusion holds independently of the critical level of LW radiation and even when medium-weight seeds are allowed to form in higher metallicity galaxies, via the so-called super-competitive accretion scenario. Our study suggests that the genealogy of SMBHs is characterized by a rich variety of BH progenitors, which represent only a small fraction (< 10 - 20%) of all the BHs that seed galaxies at z > 15
Global torques and stochasticity as the drivers of massive black hole pairing in the young universe
No full textThe forthcoming Laser Interferometer Space Antenna (LISA) will probe the population of coalescing massive black hole (MBH) binaries up to the onset of structure formation. Here, we simulate the galactic-scale pairing of ∼106 M☉ MBHs in a typical, non-clumpy main-sequence galaxy embedded in a cosmological environment at z = 7-6. In order to increase our statistical sample, we adopt a strategy that allows us to follow the evolution of six secondary MBHs concomitantly. We find that the magnitude of the dynamical-friction-induced torques is significantly smaller than that of the large-scale, stochastic gravitational torques arising from the perturbed and morphologically evolving galactic disc, suggesting that the standard dynamical friction treatment is inadequate for realistic galaxies at high redshift. The dynamical evolution of MBHs is very stochastic, and a variation in the initial orbital phase can lead to a drastically different time-scale for the inspiral. Most remarkably, the development of a galactic bar in the host system either significantly accelerates the inspiral by dragging a secondary MBH into the centre, or ultimately hinders the orbital decay by scattering the MBH in the galaxy outskirts. The latter occurs more rarely, suggesting that galactic bars overall promote MBH inspiral and binary coalescence. The orbital decay time can be an order of magnitude shorter than what would be predicted relying on dynamical friction alone. The stochasticity and the important role of global torques have crucial implications for the rates of MBH coalescences in the early Universe: both have to be accounted for when making predictions for the upcoming LISA observatory
Myrcia ovata Cambess., Fl. Bras. Merid.
No full text5.12. Myrcia ovata Cambess., Fl. Bras. Merid. 2: 319. 1832 (type: "In silvis caeduis prope pagum Aldea de S. Pedro et praedium S. Jacinto in provinciae Rio de Janeiro ", Saint-Hilaire s.n., P). = Myrcia atropunctata Kiaersk, Enum. Myrt. Bras.: 68. 1893 (type: Rio de Janeiro, Glaziou 11982, C, R). Syn. nov.Published as part of Sobral, M., Souza, M. C., Mazine-Capelo, F. & Lucas, E., 2010, Nomenclatural notes on Brazilian Myrtaceae, pp. 51-58 in Phytotaxa 8 on page 56, DOI: 10.11646/phytotaxa.8.1.6, http://zenodo.org/record/489525
Compositional analysis of dietary patterns
No full textSolans, M., Coenders, G., Marcos-Gragera, R. , Castelló, A., Gràcia-Lavedan, E. , Benavente, Y., Moreno, V., Pérez-Gómez, B., Amiano, P. , Fernández-Villa, T. , Guevara, M., Gómez-Acebo, I., Fernández-Tardón, G. , Vanaclocha-Espi, M. , Chirlaque, M.D., Capelo, R., Barrios, R., Aragonés, N. , Molinuevo, A., Vitelli-Storelli, F., Castilla, J., Dierssen-Sotos, T. , Castaño-Vinyals, G. , Kogevinas, M., Pollán, M., Saez, M
Night shift work and stomach cancer risk in the MCC-Spain study
No full textGyarmati, G., Turner, M.C., Castaño-Vinyals, G., Espinosa, A., Papantoniou, K., Alguacil, J., Costas, L., Pérez-Gómez, B., Martin Sanchez, V., Ardanaz, E., Moreno, V., Gómez-Acebo, I., Fernández-Tardon, G., Villanueva Ballester, V., Capelo, R., Chirlaque, M.-D., Santibáñez, M., Pollán, M., Aragonés, N., Kogevinas, M
Barred galaxies in cosmological zoom-in simulations: the importance of feedback
No full textBars are a key factor in the long-term evolution of spiral galaxies, in their unique role in redistributing angular momentum and transporting gas and stars on large scales. The Eris-suite simulations are cosmological zoom-in, N-body, smoothed-particle hydrodynamic simulations built to follow the formation and evolution of a Milky Way-sized galaxy across the build-up of the large scale structure. Here we analyse and describe the outcome of two particular simulations taken from the Eris suite – ErisBH and Eris2k – which mainly differ in the prescriptions employed for gas cooling, star formation, and feedback from supernovae and black holes. Our study shows that the enhanced effective feedback in Eris2k, due to the collective effect of the different micro-physics implementations, results in a galaxy which is less massive than its ErisBH counterpart till z ∼ 1. However, when the stellar content is large enough so that global dynamical instabilities can be triggered, the galaxy in Eris2k develops a stronger and more extended bar with respect to ErisBH. We demonstrate that he structural properties and time evolution of the two bars are very different. Our results highlight the importance of accurate sub-grid prescriptions in cosmological zoom-in simulations of the process of galaxy formation and evolution, and the possible use of a statistical sample of barred galaxies to assess the strength of the stellar feedback
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