Sergio Martin-Alvarez
Kavli Institute for Particle Astrophysics and Cosmology
KIPAC - Stanford University
MY RESEARCH PROJECTS
Below you can find a short description of what I have done and what my main results were for some of the research projects I have led during the last few years.
Figure: relative effect of baryonic feedback on the matter power spectrum of Fable (coloured), compared with that of other large simulation collaborations (blue tones).
Stirring the Cosmic Pot - How different AGN models affect the matter power spectrum
S. Martin-Alvarez, V. Iršič, S. Koudmani, et al. submitted
Using Fable simulations featuring AGN model variations (Hendel et al. 2018), I investigate how feedback affects the matter power spectrum (MPS) across times and scales. I found Quasar mode feedback dominates suppression at early times and small scales, whereas the Radio mode dominates at late times and large scales.
While AGN primarily suppress the MPS by reducing power inside haloes at low redshift, at earlier times the Quasar mode has a notable impact outside haloes. I also showed how selecting galaxies according to their black hole mass better probes power suppression.
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Figure: comparison of far infrared (left) vs radio (right) total intensity as observed by SOFIA and VLA, respectively. Overlaid cyan quivers showcase observed polarization (rotated 90º).
Tomographic comparison of far infrared and radio emission with simulated galaxies
S. Martin-Alvarez, E. Lopez-Rodriguez, SALSA, et al. 2024a
Using some of my previous high-resolution MHD cosmological simulations, I generate and compared detailed polarimetric observations of radio synchrotron and far infrared emission from galaxies.
In addition to beautifully reproduce the qualitative appearance of observed galaxies (see e.g. R. Beck's or E. Lopez-Rodriguez's SALSA observations), I showed how radio emerges from large scale (300 pc and above) and neutral medium, and FIR from small scales (10 pc and possibly below) and cold medium. I characterised the disk emission half-thickness of each as ~230pc (radio) and 110pc (FIR).
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Figure: front view of the Pandora suite presentation. It showcases the high-resolution, and comprehensive physical view provided by including all these additional physics.
The Pandora Project - I. Radiation, cosmic rays and magnetism in galaxy formation
S. Martin-Alvarez, D. Sijacki, M. Haehnelt, et al. 2023
Galaxy formation recognises magnetism, cosmic rays and radiative transfer as fundamental galaxy formation physics, despite these are frequently unaccounted for in modern simulations.
With my new Pandora simulations, I pioneered the first extensive suite of high-resolution models including all these physics and all their possible separate combinations. I show how they naturally lead to more realistic galaxies, providing a promising avenue for the next generation of galaxy formation simulations.
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Figure: comparison of the uniform resolution (top row) vs quasi-Lagrangian refinement (bottom row), showcasing the striking impact. Rightmost column shows a cosmological view of the galaxy.
Towards convergence of turbulence and magnetic amplification in galaxy simulations
S. Martin-Alvarez, J. Devriendt, A. Slyz, et al. 2022
MHD and turbulence are extremely complicated to capture, particularly in galaxy simulations, where cosmological, galaxy formation and ISM processes demand resolving a vast scales range. Even galaxy simulations with exquisite MHD solvers such as RAMSES appear at odds with turbulent theoretical predictions.
I showed how this tension with theoretical expectations is solved by simulating galaxies with uniform resolution, leading to resolved ISM turbulence, magnetic energy amplification and rich small-scale structure.
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Figure: comparison of two galaxies magnetised with both astrophysical and with either strong (top row) or weak (bottom row) primordial magnetic fields. From left to right columns show: optical view of the galaxy; intrinsic gas density (cyan) and magnetisation (green) view; magnetic fields separated into primordial (green) and astrophysical (red), with colours compounding depending on their proportion - the blue colour corresponds to constructive energetic interference of the two fields
Unraveling the Origin of Magnetic Fields in Galaxies
S. Martin-Alvarez, H. Katz, D. Sijacki et al. 2021
I generate novel simulations using magnetic tracers, capable of separately tracing the evolution of astrophysical and primordial magnetic fields, to investigate the elusive nature of magnetic fields in galaxies.
I found that if magnetisation from the early Universe was strong enough, the resulting magnetic fields will survive alongside those of astrophysical origin, predominantly residing in (galactic) large-scales, and permeating metal-poor, colder gas. This finding points to a new avenue to study primordial magnetism in our Universe through a detailed understanding of magnetic fields in galaxies.
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Figure: galaxy visualisation of the same galaxy simulated with increasingly stronger magnetic fields (from left to right). This leads to galaxies that shrink and concentrate in size.
How strong magnetisation of galaxies shrinks their sizes
S. Martin-Alvarez, A. Slyz, J. Devriendt, et al. 2020
I generated an extended sample of simulations varying initial configuration and degree of magnetisation of galaxies, as well as feedback prescription. Depending on their strength magnetic fields are capable of significantly impacting global galactic properties.
Their primary effect is concentrating the size and star formation of galaxies towards their centre, reducing their rotational support. These effects are distinguishable with JWST observations.
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Figure: magnetic energy of the galaxy growing over time for three different supernova explosion models. Energy increases following three time phases.
Three-phase magnetic field amplification in galaxies
S. Martin-Alvarez, J. Devriendt, A. Slyz, et al. 2018
I generated and analysed three simulations of the NUT galaxy under different supernova prescriptions. I showed how all models exhibit significant magnetic field amplification, separated in three phases: galaxy collapse, accretion-driven amplification, and feedback driven amplification. Different feedback models lead to varying turbulent amplification rates.
I also address the role of mergers on amplification and perform a resolution study.
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