Browsing by Author "Padilla, N. D."

Now showing 1 - 6 of 6
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    Dark matter from primordial black holes would hold charge
    (2023) Araya, I. J.; Padilla, N. D.; Rubio, M. E.; Sureda, J.; Magana, J.; Osorio, L.
    We explore the possibility that primordial black holes (PBHs) contain electric charge down to the present day. We find that PBHs should hold a non-zero net charge at their formation, due to either Poisson fluctuations at horizon crossing or high-energy particle collisions. Although initial charge configurations are subject to fast discharge processes through particle accretion or quantum particle emission, we show that maximally rotating PBHs could produce magnetic fields able to shield them from discharge. Moreover, given that electrons are the lightest and fastest charge carriers, we show that the plasma within virialised dark matter haloes can endow PBHs with net negative charge. We report charge-to-mass ratios between 10-31 C/kg and 10-15 C/kg for PBHs within the mass windows that allow them to constitute the entirety of the dark matter in the Universe.
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    Gravitational redshifting of galaxies in the SPIDERS cluster catalogue
    (2021) Mpetha, C. T.; Collins, C. A.; Clerc, N.; Finoguenov, A.; Peacock, J. A.; Comparat, J.; Schneider, D.; Capasso, R.; Damsted, S.; Furnell, K.; Merloni, A.; Padilla, N. D.; Saro, A.
    Data from the SPectroscopic IDentification of ERosita Sources (SPIDERS) are searched for a detection of the gravitational redshifting of light from similar to 20 000 galaxies in similar to 2500 galaxy clusters using three definitions of the cluster centre: its Brightest Cluster Galaxy (BCG), the redMaPPer identified Central Galaxy (CG), or the peak of X-ray emission. Distributions of velocity offsets between galaxies and their host cluster's centre, found using observed redshifts, are created. The quantity (Delta) over cap, the average of the radial velocity difference between the cluster members and the cluster systemic velocity, reveals information on the size of a combination of effects on the observed redshift, dominated by gravitational redshifting. The change of (Delta) over cap with radial distance is predicted for SPIDERS galaxies in General Relativity (GR), and f(R) gravity, and compared to the observations. The values of (Delta) over cap = -13.5 +/- 4.7 kms(-1), (Delta) over cap = -12.5 +/- 5.1 kms(-1), and (Delta) over cap = -18.6 +/- 4.8 kms(-1) for the BCG, X-ray, and CG cases, respectively, broadly agree with the literature. There is no significant preference of one gravity theory over another, but all cases give a clear detection (>2.5 sigma) of (Delta) over cap. The BCG centroid is deemed to be the most robust method in this analysis, due to no well-defined central redshift when using an X-ray centroid, and CGs identified by redMaPPer with no associated spectroscopic redshift. For future gravitational redshift studies, an order-of-magnitude more galaxies, similar to 500 000, will be required - a possible feat with the forthcoming Vera C. Rubin Observatory, Euclid and eROSITA.
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    Halo merger tree comparison: impact on galaxy formation models
    (2022) Gomez, Jonathan S.; Padilla, N. D.; Helly, J. C.; Lacey, C. G.; Baugh, C. M.; Lagos, C. D. P.
    We examine the effect of using different halo finders and merger tree building algorithms on galaxy properties predicted using the galform semi-analytical model run on a high resolution, large volume dark matter simulation. The halo finders/tree builders hbt, rockstar, subfind, and VELOCI raptor differ in their definitions of halo mass, on whether only spatial or phase-space information is used, and in how they distinguish satellite and main haloes; all of these features have some impact on the model galaxies, even after the trees are post-processed and homogenized by galform. The stellar mass function is insensitive to the halo and merger tree finder adopted. However, we find that the number of central and satellite galaxies in galform does depend slightly on the halo finder/tree builder. The number of galaxies without resolved subhaloes depends strongly on the tree builder, with VELOCIraptor, a phase-space finder, showing the largest population of such galaxies. The distributions of stellar masses, cold and hot gas masses, and star formation rates agree well between different halo finders/tree builders. However, because VELOCIraptor has more early progenitor haloes, with these trees galform produces slightly higher star formation rate densities at high redshift, smaller galaxy sizes, and larger stellar masses for the spheroid component. Since in all cases these differences are small we conclude that, when all of the trees are processed so that the main progenitor mass increases monotonically, the predicted galform galaxy populations are stable and consistent for these four halo finders/tree builders.
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    Magnetic field generation from PBH distributions
    (2021) Araya, I. J.; Rubio, M. E.; San Martin, M.; Stasyszyn, F. A.; Padilla, N. D.; Magana, J.; Sureda, J.
    We introduce a statistical method for estimating magnetic field fluctuations generated from primordial black hole (PBH) populations. To that end, we consider monochromatic and extended Press-Schechter PBH mass functions, such that each constituent is capable of producing its own magnetic field due to some given physical mechanism. Assuming a linear correlation between magnetic field fluctuations and matter overdensities, our estimates depend on the mass function, the physical field generation mechanism by each PBH constituent, and the characteristic PBH separation. After computing the power spectrum of magnetic field fluctuations, we apply our formalism to study the plausibility that two particular field generation mechanisms could have given rise to the expected seed fields according to current observational constraints. The first mechanism is the Biermann battery and the second one is due to the accretion of magnetic monopoles at PBH formation, constituting magnetic PBHs. Our results show that, for monochromatic distributions, it does not seem to be possible to generate sufficiently intense seed fields in any of the two field generation mechanisms. For extended distributions, it is also not possible to generate the required seed field by only assuming a Biermann battery mechanism. In fact, we report an average seed field by this mechanism of about 10(-47) G, at z = 20. For the case of magnetic monopoles, we instead assume that the seed values from the literature are achieved and calculate the necessary number density of monopoles. In this case, we obtain values that are below the upper limits from current constraints.
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    Redshift evolution of the dark matter haloes shapes
    (2023) Cataldi, P.; Pedrosa, S. E.; Tissera, P. B.; Artale, M. C.; Padilla, N. D.; Dominguez-Tenreiro, R.; Bignone, L.; Gonzalez, R.; Pellizza, L. J.
    In this work, we aim at investigating the morphology evolution of Milky Way mass-like dark matter haloes selected from the cielo and IllustrisTNG projects. The connection between halo shapes and their environment has been studied in previous works at z = 0 but their connection remains yet to be fully understood. We focus on the evolution across cosmic time of the halo shapes and the relation with the infalling material, using hydrodynamical simulations. Our findings show that haloes tend to be more triaxial at earlier times as a consequence of stronger accretion in the direction of the filaments. As the haloes evolve towards a dominant isotropic accretion mode and relaxation, their shape at 20 per cent of the virial radius becomes more spherical. In agreement with previous results, baryons have an important effect within the inner regions of the haloes, driving them from triaxial to rounder shapes. We also find a correlation between the strength of the quadrupole infalling mode and the degree of ellipticity of the haloes: as the filament strength decreases steadily with redshift, the haloes became more spherical and less elliptical.
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    Satellite galaxies in groups in the CIELO Project I. Gas removal from galaxies and its re-distribution in the intragroup medium
    (2022) Rodriguez, S.; Garcia Lambas, D.; Padilla, N. D.; Tissera, P.; Bignone, L.; Dominguez-Tenreiro, R.; Gonzalez, R.; Pedrosa, S.
    We study the impact of the environment on galaxies as they fall in and orbit in the potential well of a Local Group (LG) analogue, following them with high cadence. The analysis is performed on eight disc satellite galaxies from the CIELO suite of hydrodynamical simulations. All galaxies have stellar masses within the range [10(8.1)-10(9.56)] M(circle dot)h(-1). We measure tidal torques, ram pressure, and specific star formation rates (sSFRs) as a function of time, and correlate them with the amount of gas lost by satellites along their orbits. Stronger removal episodes occur when the disc plane is oriented perpendicular to the direction of motion. More than one peripassage is required to significantly modify the orientations of the discs with respect to the orbital plane. The gas removed during the interaction with the central galaxies may also be found opposite to the direction of motion, depending on the orbital configuration. Satellites are not totally quenched when the galaxies reach their first peripassage and continue forming about 10 per cent of the final stellar mass after this event. The fraction of removed gas is found to be the product of the joint action of tidal torque and ram pressure, which can also trigger new star formation activity and subsequent supernova feedback.