Browsing by Author "Sillero, Emanuel"

Now showing 1 - 4 of 4
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    Modelling H2 and its effects on star formation using a joint implementation of gadget-3 and KROME
    (2021) Sillero, Emanuel; Tissera, Patricia B.; Lambas, Diego G.; Bovino, Stefano; Schleicher, Dominik R.; Grassi, Tommaso; Bruzual, Gustavo; Charlot, Stephane
    We present p-gadget3-k, an updated version of gadget-3, that incorporates the chemistry package krome. p-gadget3-k follows the hydrodynamical and chemical evolution of cosmic structures, incorporating the chemistry and cooling of H-2 and metal cooling in non-equilibrium. We performed different runs of the same ICs to assess the impact of various physical parameters and prescriptions, namely gas metallicity, molecular hydrogen formation on dust, star formation recipes including or not H-2 dependence, and the effects of numerical resolution. We find that the characteristics of the simulated systems, both globally and at kpc-scales, are in good agreement with several observable properties of molecular gas in star-forming galaxies. The surface density profiles of star formation rate (SFR) and H-2 are found to vary with the clumping factor and resolution. In agreement with previous results, the chemical enrichment of the gas component is found to be a key ingredient to model the formation and distribution of H-2 as a function of gas density and temperature. A star formation algorithm that takes into account the H-2 fraction together with a treatment for the local stellar radiation field improves the agreement with observed H-2 abundances over a wide range of gas densities and with the molecular Kennicutt-Schmidt law, implying a more realistic modelling of the star formation process.
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    On the Evolutionary History of a Simulated Disk Galaxy as Seen by Phylogenetic Trees
    (2024) Silva, Danielle de Brito; Jofre, Paula; Tissera, Patricia B.; Yaxley, Keaghan J.; Jara, Jenny Gonzalez; Eldridge, Camilla J. L.; Sillero, Emanuel; Yates, Robert M.; Hua, Xia; Das, Payel; Aguilera-Gomez, Claudia; Johnston, Evelyn J.; Rojas-Arriagada, Alvaro; Foley, Robert; Gilmore, Gerard
    Phylogenetic methods have long been used in biology and more recently have been extended to other fields-for example, linguistics and technology-to study evolutionary histories. Galaxies also have an evolutionary history and fall within this broad phylogenetic framework. Under the hypothesis that chemical abundances can be used as a proxy for the interstellar medium's DNA, phylogenetic methods allow us to reconstruct hierarchical similarities and differences among stars-essentially, a tree of evolutionary relationships and thus history. In this work, we apply phylogenetic methods to a simulated disk galaxy obtained with a chemodynamical code to test the approach. We found that at least 100 stellar particles are required to reliably portray the evolutionary history of a selected stellar population in this simulation, and that the overall evolutionary history is reliably preserved when the typical uncertainties in the chemical abundances are smaller than 0.08 dex. The results show that the shapes of the trees are strongly affected by the age-metallicity relation, as well as the star formation history of the galaxy. We found that regions with low star formation rates produce shorter trees than regions with high star formation rates. Our analysis demonstrates that phylogenetic methods can shed light on the process of galaxy evolution.
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    The evolution of the oxygen abundance gradients in star-forming galaxies in the EAGLE simulations
    (2022) Tissera, Patricia B.; Rosas-Guevara, Yetli; Sillero, Emanuel; Pedrosa, Susana E.; Theuns, Tom; Bignone, Lucas
    We analyse the evolution of the oxygen abundance gradient of star-forming galaxies with stellar mass M-* >= 10(9)M(circle dot) in the EAGLE simulation over the redshift range z = [0, 2.5]. We find that the median metallicity gradient of the simulated galaxies is close to zero at all z, whereas the scatter around the median increases with z. The metallicity gradients of individual galaxies can evolve from strong to weak and vice versa, since mostly low-metallicity gas accretes on to the galaxy, resulting in enhanced star formation and ejection of metal-enriched gas by energy feedback. Such episodes of enhanced accretion, mainly dominated by major mergers, are more common at higher z and hence contribute to increasing the diversity of gradients. For galaxies with negative metallicity gradients, we find a redshift evolution of similar to -0.03 dex kpc(-1)/delta z. A positive mass dependence is found at z <= 0.5, which becomes slightly stronger for higher redshifts and, mainly, for M-* < 10(9.)(5) M-circle dot. Only galaxies with negative metallicity gradients define a correlation with galaxy size, consistent with an inside-out formation scenario. Our findings suggest that major mergers and/or significant gas accretion can drive strong negative or positive metallicity gradients. The first ones are preferentially associated with disc-dominated galaxies, and the second ones with dispersion-dominated systems. The comparison with forthcoming observations at high redshift will allow a better understanding of the potential role of metallicity gradients as a chemical probe of galaxy formation.
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    Understanding the Early Stages of Galaxy Formation Using Very Metal-poor Stars from the Hamburg/ESO Survey
    (2023) Carollo, Daniela; Christlieb, Norbert; Tissera, Patricia B.; Sillero, Emanuel
    We explore the chemodynamical properties of a sample of very metal-poor (VMP) stars selected from the Hamburg/ESO survey, matched with Gaia EDR3, in the phase space identified by the three integrals of motion (L-z , E, I-3). Disk and halo orbits are separated by using the criteria defined in Carollo & Chiba. We found 26 stars with [Fe/H] <= -2.5 possessing disk kinematics, of which 13 are extremely metal-poor. At these metallicities, the number of stars with disk kinematics is three times its retrograde counterpart. In the same range of metallicity we also identified 37 halo stars most tightly bound to the gravitational potential of the progenitor halo. The origins of these stars are investigated by comparing the observational results with simulated galaxies from the Aquarius Project and the IllustrisTNG simulations. We found two mechanisms of formation of VMP stars with disk kinematics: accretion from early satellites (which is dominant), and in situ formation. These stars are very old, with ages >12.5 Gyr (z > 5), and they are alpha-enriched. Accretion and in situ formation are also found for the retrograde counterparts, with accretion also being the dominant mode. Contributing accreted satellites have stellar masses in the range 10(6)-10(9) M-circle dot and are very gas-rich. The most bound halo stars are the oldest detected, with a median age of similar to 13.3 Gyr (z similar to 11), and are alpha-enriched. Our finding clearly shows that very old, VMP stars store important information on the first stages of assembly of our Galaxy and its halo.