Universidad Autonoma de Madrid
Universidad Autónoma de Madrid
Deparment of Theoretical Physics

Facultad de Ciencias Departamento de Fisica Teorica Grupo de Astrofisica

Yago Ascasibar - Research

Scientific interests

Most of my research belongs to the realm of Extragalactic Astrophysics. In particular, I am interested in galaxy formation and evolution, understood in a very broad sense. Although my work is mainly of theoretical nature, comparison with observations is always sought, often involving measurements at very different wavelengths. In this respect, I have greatly benefited from many discussions, and sometimes close collaboration, with observational astronomers, as well as scientists from other fields (mathematicians and particle physicists).

Here I list just a few (not completely independent) topics where I have tried to add some noise to the discussion:

  1. DARK MATTER
    • Structure of dark matter haloes

      In the current paradigm of cosmic structure formation, all galaxies are thought to reside in a dark matter halo that contains most of the mass. The physical properties of these objects has been extensively studied during the past three decades using different techniques, and N-body simulations are arguably one of the most powerful. I am mostly interested in the internal dynamics of simulated dark matter haloes as well as their structure in the six-dimensional phase space of particle positions and velocities.

      Nevertheless, the hierarchical assembly of dark matter haloes is an extremely violent process, and the results of cosmological simulations are often difficult to interpret. The physical origin of their dynamical structure is still unknown, and there are currently two opposite views: in one of them, it is (re)set during galaxy-galaxy mergers; in the other (that I support), it merely reflects the initial conditions in the primordial universe, and mergers play only a minor role. In this scenario, the evolution of a dark matter halo can be understood in terms of a relatively simple model that assumes spherical symmetry.

    • Nature of dark matter particles

      In addition to the traditional methods based on its gravitational influence, the last few years have witnessed a growing interest in indirect dark matter detection through the emission of photons and high-energy particles during dark matter annihilation or decay. I am interested in the expected signal at different wavelengths (from radio to gamma rays) for different dark matter candidates, but also on less standard (and more astrophysical) issues such as the potential effects on the rotation curves and the star formation activity in galaxies, or the cooling flows in galaxy clusters.

  2. GALAXIES
    • Star formation

      The physics of galaxy formation is much more complex than the gravitational interaction that governs the dynamics of dark matter particles. Among other things, stars inject a significant amount of energy into the surrounding gas; although emphasis is usually put on supernova explosions, I am personally more concerned with other effects, such as turbulence, magnetic fields, cosmic rays, or the photoionization and photodissociation of hydrogen.

      One of the key open questions in the field is the main mechanism that regulates star formation in galaxies. On the smallest scales, the HII regions caused by the ultraviolet radiation of young stars constitute ideal laboratories to compare the predictions of detailed photoionization models and observational data at different wavelengths. On galactic scales, simpler models may be used in order to gain some information about the underlying physics from large observational samples.

    • Chemical evolution

      Stars are also responsible for the synthesis of most chemical elements. The abundance of each chemical species, as well as their spatial distribution throughout a galaxy, provide additional constraints on the path it has followed to reach its present state. In particular, self-consistent models of star formation, chemical evolution, and stellar population synthesis may be used to investigate the infall and ouflow of gas in dwarf irregular and blue compact dwarf galaxies, suggesting that, contrary to the common view, these objects are able to retain most of their metals.

    • Statistics

      Another piece of the puzzle is given by the statistics of the overall galaxy population, whose study has been made possible thanks to the advent of large systematic surveys. Models should not only match the observable properties of individual galaxies, but also integrated quantities such as the cosmic star formation history or the diffuse extragalactic gackground light. The luminosity function in different bands, as well as the observed correlations between luminosities, colours, masses of different phases (dark matter, neutral and molecular gas, stars of different ages), chemical abundances, etc., also have to be reproduced at all redshifts.

      On the other hand, the mere existence of all these correlations raises the question of the number of degrees of freedom (i.e. independent parameters) that are necessary in order to describe a galaxy. It seems that the optical spectra of normal galaxies follow a well-defined sequence in spectral space (which could be interpreted as a one-to-one mapping between the mass of the dark matter halo and all the galaxy properties), whereas optically-active galaxies are arranged in a roughly orthogonal branch that intersects the main sequence at the location of the "green valley" (consistent with a temporary phase, associated to the exhaustion of cold gas, the termination of star formation, and the transition from the blue cloud to the red sequence).

  3. GALAXY CLUSTERS
    • Structure of the intracluster medium

      Unlike dark matter haloes, galaxies living in different environments feature very distinctive properties, and one of the possible reasons is that they are inmersed in the hot, diffuse gas of the intracluster medium. Although the density and temperature of the gas can display a remarkable degree of structure (such as shock waves, or cold fronts of different types), it is possible to capture the overall properties of clusters (most importantly, their X-ray emission and scaling relations, but also the signal at radio and microwave frequencies) by means of a relatively simple analytical model.

  4. NUMERICAL METHODS
    • Politeware

      Most of the work along any of the lines above involves a significant amount of numerical effort. Quite often, the analysis of numerical data also calls for fairly sophisticated - sometimes completely new -algorithms, either because of the complexity of the problem or because of its scale (i.e. memory and/or CPU requirements). Source code is publicly available as politeware in all cases.


Publications

An up-to-date list from the NASA/ADS database may be obtained here.


Research projects

  • October 2013 - September 2017: "Study of Emission Line Galaxies with Integral Field Spectroscopy" (SELGIFS)
    EU Marie Curie Actions (FP7-PEOPLE-2013-IRSES-612701)
    Global Coordinator: Ángeles Díaz
    Scientific project Manager: Yago Ascasibar
  • January 2014 - December 2016: "El papel de los estallidos de formación estelar en la formación y evolución de galaxias: Estallidos 5"
    Co-PIs: Ángeles Díaz, Yago Ascasibar (MINECO, Spain, AYA2013-47742-C4-3-P)
  • January 2014 - December 2015: "The chemical and dynamical structure of disk galaxies"
    Co-PIs: Yago Ascasibar, Cecilia Scannapieco (DAAD, Germany, PPP-Spain-57050803)
  • January 2011 - December 2013: "Estallidos y su huella en la evolución cósmica de las galaxias"
    PI: Ángeles Díaz (MICINN, Spain, AYA 2010-21887-C04-03)
  • January 2010 - December 2012: "Astrofísica y desarrollos tecnológicos en la Comunidad de Madrid"
    PI: José M. Mas Hesse (CAM, Spain, P2009/ESP-1496)
  • January 2008 - December 2010: "Estallidos de formación estelar en galaxias, 3ª fase"
    PI: Ángeles Díaz (MEC, Spain, AYA 2007-67965-C03-03)
  • January 2008 - December 2010: "Astrophysical signatures of dark matter: its nature, the structure of haloes, and galaxy formation"
    PI: Yago Ascasibar (DFG, Germany, AS 312/1-1)
  • January 2008 - December 2009: "Structure formation in constrained simulations"
    PI: Stefan Gottlöber (DAAD, Germany, PPP-USA 315-sc-ab)
  • November 2007: "The phase-space structure of dark matter haloes"
    PI: Yago Ascasibar (ESF, EU, Astrosim/2027)
  • October 2006 - September 2009: "Astropartículas en el universo: materia oscura, neutrinos y rayos cósmicos"
    PI: Gustavo Yepes (MEC, Spain, FPA 2006-01105)
  • October 2006 - September 2007: "Estudio multifrecuencial de cúmulos de galaxias"
    PI: José M. Diego (MEC, Spain, AYA 2006-06266)
  • September 2005 - August 2007: "The most interesting cluster in the universe"
    PI: Maxim Markevitch (NASA, USA, G04-5152-X)
  • September 2003 - August 2005: "Gas density discontinuities in merging clusters"
    PI: Maxim Markevitch (NASA, USA, G02-3164-X)
  • January 2000 - December 2004: "The nature of dark matter"
    PI: Joseph I. Silk (Leverhume Trust, UK, F/08776A)
  • January 2003 - December 2004: "Cúmulos de galaxias: evolución, dinámica y efecto Sunyaev-Zeldovich"
    PI: Fernando Atrio Barandela (MCyT, Spain, HA 02-84)
  • January 2001 - December 2002: "Formación y evolución de cúmulos de galaxias en diferentes marcos cosmológicos"
    PI: Gustavo Yepes (MCyT, Spain, HA 2000-0026)
  • January 2001 - December 2003: "Estudio de la formación y evolución de galaxias en diferentes épocas cosmológicas y de la estructura a gran escala del universo"
    PI: Ángeles I. Díaz (MCyT, Spain, AYA 2000-0973)


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