1,721,002 research outputs found
Formation of disc galaxies from cosmological simulations: galactic outflows and chemical evolution
Full text linkIn this Thesis, I study the formation of late-type galaxies and the role that feedback from stars
and supermassive black holes (SMBHs) plays in galaxy evolution across cosmic time.
By carrying out cosmological hydrodynamical simulations, I investigate how different processes,
such as the cosmological gas accretion from the large scale environment, star formation and chemical
enrichment, stellar and AGN (Active Galactic Nucleus) feedback, affect the early stages of forming galaxies
and contribute to determine their present-day properties.
Driven by the challenging task of simulating late-type galaxies with a limited bulge and a dominant disc
in a cosmological context, I study the impact of galactic outflow modelling on the formation and evolution
of a disc galaxy. I find that galactic outflows regulate the timing of gas accretion and
determine the star formation history of the forming galaxy.
Also, I quantify the strong interplay between the adopted hydrodynamical scheme and the
sub-resolution model describing star formation and stellar feedback.
Throughout this Thesis, I devote particular emphasis to connect chemical evolution and gas dynamics,
in order to interpret observations of metal abundance in the interstellar medium (ISM) and
circumgalactic medium (CGM). I investigate the metal content of gas and stars, and explore how the variation
of the essential elements contributing to define the model of chemical evolution determine final metal abundance
trends. The investigation that I present is guided by observations and focusses on the results at redshift z = 0,
with particular emphasis on the role played by the high-mass end of the IMF.
Moreover, I introduce a novel methodology to generate synthetic stars from star particles.
The technique that I developed takes properties of star particles from simulations as input
and allows to obtain a catalogue of mock stars, provided with photometric properties, whose
characteristics are drawn from the input features.
The ultimate goal of this method is to translate the populations of star particles of a simulation
into stellar populations, thereby enabling a direct and accurate comparison with observations.
This technique will be of paramount importance with ongoing survey data
releases (e.g. GAIA and surveys of resolved stellar populations).
Also, I investigate the role of AGN feedback in regulating the formation and evolution of late-type galaxies.
I introduce a new model aimed at investigating the interaction between the central SMBH and the
various gas phases which coexist in the ISM of the host galaxy
Dynamical friction and evolution of black holes in cosmological simulations: a new implementation in OpenGadget3
Full text linkFil: Damiano, Alice. Dipartimento di Fisica dell’Università di Trieste. Sez. di Astronomia; Italy.Fil: Damiano, Alice. Istituto Nazionale di Astrofisica. Osservatorio Astronomico di Trieste; Italy.Fil: Damiano, Alice. Istituto Nazionale di Astrofisica. Instituto Nazionale di Fisica Nucleare; Italy.Fil: Damiano, Alice. Italian Research Center on High Performance Computing. Big Data and Quantum Computing; Italy.Fil: Valentini, Milena. Dipartimento di Fisica dell’Università di Trieste. Sez. di Astronomia; Italy.Fil: Valentini, Milena. Istituto Nazionale di Astrofisica. Osservatorio Astronomico di Trieste; Italy.Fil: Valentini, Milena. Istituto Nazionale di Astrofisica. Instituto Nazionale di Fisica Nucleare; Italy.Fil: Valentini, Milena. Italian Research Center on High Performance Computing. Big Data and Quantum Computing; Italy.Fil: Borgani, Stefano. Dipartimento di Fisica dell’Università di Trieste. Sez. di Astronomia; Italy.Fil: Borgani, Stefano. Istituto Nazionale di Astrofisica. Osservatorio Astronomico di Trieste; Italy.Fil: Borgani, Stefano. Institute for Fundamental Physics of the Universe; Italy.Fil: Borgani, Stefano. Istituto Nazionale di Astrofisica. Instituto Nazionale di Fisica Nucleare; Italy.Fil: Borgani, Stefano. Italian Research Center on High Performance Computing. Big Data and Quantum Computing; Italy.Fil: Tornatore, Luca. Istituto Nazionale di Astrofisica. Osservatorio Astronomico di Trieste; Italy.Fil: Tornatore, Luca. Italian Research Center on High Performance Computing. Big Data and Quantum Computing; Italy.Fil: Murante, Giuseppe. Istituto Nazionale di Astrofisica. Osservatorio Astronomico di Trieste; Italy.Fil: Murante, Giuseppe. Institute for Fundamental Physics of the Universe; Italy.Fil: Murante, Giuseppe. Italian Research Center on High Performance Computing. Big Data and Quantum Computing; Italy.Fil: Ragagnin, Antonio. Institute for Fundamental Physics of the Universe; Italy.Fil: Ragagnin, Antonio. Osservatorio di Astrofisica e Scienza dello Spazio di Bologna; Italy.Fil: Ragagnin, Antonio. Alma Mater Studiorum Università di Bologna. Dipartimento di Fisica e Astronomia "Augusto Righi"; Italy.Fil: Ragone-Figueroa, Cinthia. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina.Fil: Ragone-Figueroa, Cinthia. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Astronomía Teórica y Experimental; Argentina.Fil: Ragone-Figueroa, Cinthia. Istituto Nazionale di Astrofisica. Osservatorio Astronomico di Trieste; Italy.Fil: Dolag, Klaus. Universitäts-Sternwarte München; Germany.Fil: Dolag, Klaus. Max-Plank-Institut für Astrophysik; Germany.We implement a sub-resolution prescription for the unresolved dynamical friction onto black holes (BHs) in the OpenGadget3 code. We carry out cosmological simulations of a volume of 16 cMpc3 and zoom-ins of a galaxy group and of a galaxy cluster. The advantages of our new technique are assessed in comparison to commonly adopted methods to hamper spurious BH displacements, i.e. repositioning onto a local minimum of the gravitational potential and ad-hoc boosting of the BH particle dynamical mass. The newly-introduced dynamical friction correction provides centering of BHs on host halos which is at least comparable with the other techniques. It predicts half as many merger events with respect to the repositioning prescription, with the advantage of being less prone to leave sub-structures without any central BH. Simulations featuring our dynamical friction prescription produce a smaller (by up to 50% with respect to repositioning) population of wandering BHs and final BH masses in good agreement with observations. As for individual BH-BH interactions, our dynamical friction model captures the gradual inspiraling of orbits before the merger occurs. By contrast, the repositioning scheme, in its most classical renditions considered, describes extremely fast mergers, while the dynamical mass misrepresents the BHs' dynamics, introducing numerical scattering between the orbiting BHs. Given its performances in describing the centering of BHs within host galaxies and the orbiting of BH pair before their merging, our dynamical friction correction opens interesting applications for an accurate description of the evolution of BH demography within cosmological simulations of galaxy formation at different cosmic epochs and within different environments.info:eu-repo/semantics/acceptedVersionFil: Damiano, Alice. Dipartimento di Fisica dell’Università di Trieste. Sez. di Astronomia; Italy.Fil: Damiano, Alice. Istituto Nazionale di Astrofisica. Osservatorio Astronomico di Trieste; Italy.Fil: Damiano, Alice. Istituto Nazionale di Astrofisica. Instituto Nazionale di Fisica Nucleare; Italy.Fil: Damiano, Alice. Italian Research Center on High Performance Computing. Big Data and Quantum Computing; Italy.Fil: Valentini, Milena. Dipartimento di Fisica dell’Università di Trieste. Sez. di Astronomia; Italy.Fil: Valentini, Milena. Istituto Nazionale di Astrofisica. Osservatorio Astronomico di Trieste; Italy.Fil: Valentini, Milena. Istituto Nazionale di Astrofisica. Instituto Nazionale di Fisica Nucleare; Italy.Fil: Valentini, Milena. Italian Research Center on High Performance Computing. Big Data and Quantum Computing; Italy.Fil: Borgani, Stefano. Dipartimento di Fisica dell’Università di Trieste. Sez. di Astronomia; Italy.Fil: Borgani, Stefano. Istituto Nazionale di Astrofisica. Osservatorio Astronomico di Trieste; Italy.Fil: Borgani, Stefano. Institute for Fundamental Physics of the Universe; Italy.Fil: Borgani, Stefano. Istituto Nazionale di Astrofisica. Instituto Nazionale di Fisica Nucleare; Italy.Fil: Borgani, Stefano. Italian Research Center on High Performance Computing. Big Data and Quantum Computing; Italy.Fil: Tornatore, Luca. Istituto Nazionale di Astrofisica. Osservatorio Astronomico di Trieste; Italy.Fil: Tornatore, Luca. Italian Research Center on High Performance Computing. Big Data and Quantum Computing; Italy.Fil: Murante, Giuseppe. Istituto Nazionale di Astrofisica. Osservatorio Astronomico di Trieste; Italy.Fil: Murante, Giuseppe. Institute for Fundamental Physics of the Universe; Italy.Fil: Murante, Giuseppe. Italian Research Center on High Performance Computing. Big Data and Quantum Computing; Italy.Fil: Ragagnin, Antonio. Institute for Fundamental Physics of the Universe; Italy.Fil: Ragagnin, Antonio. Osservatorio di Astrofisica e Scienza dello Spazio di Bologna; Italy.Fil: Ragagnin, Antonio. Alma Mater Studiorum Università di Bologna. Dipartimento di Fisica e Astronomia "Augusto Righi"; Italy.Fil: Ragone-Figueroa, Cinthia. Universidad Nacional de Córdoba. Observatorio Astronómico de Córdoba; Argentina.Fil: Ragone-Figueroa, Cinthia. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Astronomía Teórica y Experimental; Argentina.Fil: Ragone-Figueroa, Cinthia. Istituto Nazionale di Astrofisica. Osservatorio Astronomico di Trieste; Italy.Fil: Dolag, Klaus. Universitäts-Sternwarte München; Germany.Fil: Dolag, Klaus. Max-Plank-Institut für Astrophysik; Germany
AGN-stimulated cooling of hot gas in elliptical galaxies
Full text linkWe study the impact of relatively weak active galactic nucleus (AGN) feedback on the interstellar medium (ISM) of intermediate and massive elliptical galaxies. We find that the AGN activity, while globally heating the ISM, naturally stimulates some degree of hot gas cooling on scales of several kpc. This process generates the persistent presence of a cold ISM phase, with mass ranging between 104and ≳ 5 × 107M⊙, where the latter value is appropriate for group centred, massive galaxies. Widespread cooling occurs where the ratio of cooling to free-fall time before the activation of the AGN feedback satisfies tcool/tff≲ 70, that is we find a less restrictive threshold than commonly quoted in the literature. This process helps explaining the body of observations of cold gas (both ionized and neutral/molecular) in Ellipticals and, perhaps, the residual star formation detected in many early-type galaxies. The amount and distribution of the off-centre cold gas vary irregularly with time. The cold ISM velocity field is irregular, initially sharing the (outflowing) turbulent hot gas motion. Typical velocity dispersions of the cold gas lie in the range 100-200 km s-1. Freshly generated cold gas often forms a cold outflow and can appear kinematically misaligned with respect to the stars. We also follow the dust evolution in the hot and cold gas. We find that the internally generated cold ISM has a very low dust content, with representative values of the dust-to-gas ratio of 10-4-10-5. Therefore, this cold gas can escape detection in the traditional dust-absorption maps
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The role of physical and numerical viscosity in hydrodynamical instabilities
Full text linkThe evolution of the Kelvin-Helmholtz Instability (KHI) is widely used to
assess the performance of numerical methods. We employ this instability to test
both the smoothed particle hydrodynamics (SPH) and the meshless finite mass
(MFM) implementation in OpenGadget3. We quantify the accuracy of SPH and MFM in
reproducing the linear growth of the KHI with different numerical and physical
set-ups. Among them, we consider: numerical induced viscosity, and
physically motivated, Braginskii viscosity, and compare their effect on the
growth of the KHI. We find that the changes of the inferred numerical viscosity
when varying nuisance parameters such as the set-up or the number of neighbours
in our SPH code are comparable to the differences obtained when using different
hydrodynamical solvers, i.e. MFM. SPH reproduces the expected reduction of the
growth rate in the presence of physical viscosity and recovers well the
threshold level of physical viscosity needed to fully suppress the instability.
In the case of galaxy clusters with a virial temperature of K,
this level corresponds to a suppression factor of of the
classical Braginskii value. The intrinsic, numerical viscosity of our SPH
implementation in such an environment is inferred to be at least an order of
magnitude smaller (i.e. ), re-ensuring that modern SPH methods
are suitable to study the effect of physical viscosity in galaxy clusters.Comment: 22 pages, 22 figures, accepted in MNRA
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Chemical evolution of disc galaxies from cosmological simulations
Full text linkWe perform a suite of cosmological hydrodynamical simulations of disc galaxies, with zoomed-in initial conditions leading to the formation of a halo of mass M_{halo, DM} ̃eq 2 × 10^{12} M⊙ at redshift z = 0. These simulations aim at investigating the chemical evolution and the distribution of metals in a disc galaxy, and at quantifying the effect of (i) the assumed IMF, (ii) the adopted stellar yields, and (iii) the impact of binary systems originating SNe Ia on the process of chemical enrichment. We consider either a Kroupa, Tout & Gilmore (1993) or a more top-heavy Kroupa (2001) IMF, two sets of stellar yields and different values for the fraction of binary systems suitable to give rise to SNe Ia. We investigate stellar ages, SN rates, stellar and gas metallicity gradients, and stellar α-enhancement in simulations, and compare predictions with observations. We find that a Kroupa et al. (1993) IMF has to be preferred when modelling late-type galaxies in the local Universe. On the other hand, the comparison of stellar metallicity profiles and α-enhancement trends with observations of Milky Way stars shows a better agreement when a Kroupa (2001) IMF is assumed. Comparing the predicted SN rates and stellar α-enhancement with observations supports a value for the fraction of binary systems producing SNe Ia of 0.03, at least for late-type galaxies and for the considered IMFs. Adopted stellar yields are crucial in regulating cooling and star formation, and in determining patterns of chemical enrichment for stars, especially for those located in the galaxy bulge
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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