arXiv subjects

Elena Asencio

Publications and source records attributed to Elena Asencio.

6 recordsLinked to original sources

arXiv2026

The tidal features of the classical Milky Way satellites: Expected in MOND but inconsistent with cold dark matter models

Most classical satellites of the Milky Way are known to display signs of tidal disturbance (e.g. tidal tails, substructures, and distorted shapes). This cannot be explained by the standard model of cosmology due to its prediction that the dark matter haloes of the classical satellites confer them with very strong self-gravity and make them resilient to the Milky Way's gravitational tides. In this work, we estimate the tidal susceptibility of the classical satellites by comparing their half-mass radius with their theoretical tidal radius at pericentre in both the standard model and in the Milgromian dynamics (MOND) model. With this approach, we demonstrate that most classical satellites are expected to be tidally perturbed in MOND, so their observed tidal features are generally in good agreement with MOND expectations. Since gravitational tides can also enhance the velocity dispersion of the satellites, we argue that MOND can plausibly explain the unusually high velocity dispersions reported for some of the classical satellites.

astro-ph.GA↗

arXiv2026

Baryonic mass budgets in the central regions of the Bullet Cluster and their consistency with strong lensing in MOND

Strong lensing observations of the Bullet Cluster have traditionally been regarded as strong evidence for dark matter and a major challenge to Milgromian dynamics (MOND). The offset between the lensing mass and the X-ray gas centroids implies a substantial amount of unseen mass near the brightest cluster galaxies (BCGs). However, the high metallicities observed in both the intracluster gas and the massive early-type member galaxies suggest a past stellar population dominated by massive stars, whose evolved remnants contribute additional baryonic mass. This effect is naturally incorporated in the integrated galaxy-wide initial mass function (IGIMF) theory, which predicts substantially larger baryonic masses than a canonical IMF. In this work, we re-estimate the baryonic masses of the three BCG-centred core regions of the Bullet Cluster using recent JWST photometry and compare them with MOND strong-lensing masses. We derive IGIMF masses using stellar population synthesis models with constant and (self-) enriched metallicities, representing lower and upper mass limits, respectively. We find that the MOND strong-lensing masses of all three cores lie within the range predicted by the IGIMF models. These results suggest that the baryonic mass budget is consistent with MOND requirements from strong-lensing observations in the core regions of the Bullet Cluster. However, the physical viability of this scenario also depends on the spatial distribution and dynamical behavior of the remnant population, which remain to be established. More generally, regardless of the validity of MOND, the results imply that less dark matter may be required than previously inferred.

astro-ph.GA↗

arXiv2025

Investigating the origin of the Milky Way streams. A revised look at their orbital pole distribution in light of precession effects

Stellar streams around the Milky Way (MW) can provide valuable insights into its history and substructure formation. Previous studies have suggested that several MW streams could have an origin related to that of the disc of satellite galaxies (DoS) and the young halo globular clusters of the MW, given that many of these structures present a similar orbital pole orientation. In this work we test the validity of this hypothesis by revising the orbital pole distribution of the MW streams with the latest stream dataset (galstreams). For a sample of 91 streams at Galactocentric distances of $d<100$ kpc we find that the pole distribution has no preferred orbital direction. However, as we subtract the streams closer to the Galactic centre, by imposing several lower distance cuts, we find that the larger the Galactocentric distance of the streams, the higher the fraction of stream poles pointing in a direction similar to the DoS. This trend could be explained if the stream pole distribution were originally anisotropic, but precession effects displaced the orbital poles of the streams closer to the Galactic centre. From the pole distribution and the estimated precession rates of the streams in the sample, we infer that the streams nearer the Galactic centre are indeed quite likely to be affected by precession. Finally, we corroborate with hydrodynamical simulations that, even in a scenario in which the MW substructures had a common origin, an overdensity in their orbital pole direction cannot be appreciated until the selected sample also includes material at $d \gtrsim 150$ kpc.

astro-ph.GA↗

arXiv2024

The Magellanic Clouds are very rare in the IllustrisTNG simulations

The Large and Small Magellanic Cloud (LMC and SMC) form the closest interacting galactic system to the Milky Way, therewith providing a laboratory to test cosmological models in the local Universe. We quantify the likelihood for the Magellanic Clouds (MCs) to be observed within the $Λ$CDM model using hydrodynamical simulations of the IllustrisTNG project. The orbits of the MCs are constrained by proper motion measurements taken by the $Hubble~Space~Telescope$ and $Gaia$. The MCs have a mutual separation of $d_{\mathrm{MCs}}~=~24.5\,\mathrm{kpc}$ and a relative velocity of $v_{\mathrm{MCs}}~=~90.8\,\mathrm{km\,s^{-1}}$, implying a phase-space density of $f_{\mathrm{MCs,obs}}~\equiv~(d_{\mathrm{MCs}} \cdot v_{\mathrm{MCs}})^{-3}~=~9.10\times10^{-11}\,\mathrm{km^{-3}\,s^{3}\,kpc^{-3}}$. We select analogues to the MCs based on their stellar masses and distances in MW-like halos. None of the selected LMC analogues have a higher total mass and lower Galactocentric distance than the LMC, resulting in $>3.75σ$ tension. We also find that the $f_{\mathrm{MCs}}$ distribution in the highest resolution TNG50 simulation is in $3.95σ$ tension with observations. Thus, a hierarchical clustering of two massive satellites like the MCs in a narrow phase-space volume is unlikely in $Λ$CDM, presumably because of short merger timescales due to dynamical friction between the overlapping dark matter halos. We show that group infall led by an LMC analogue cannot populate the Galactic disc of satellites (DoS), implying that the DoS and the MCs formed in physically unrelated ways in $Λ$CDM. Since the $20^\circ$ alignment of the LMC and DoS orbital poles has a likelihood of $P=0.030$ ($2.17σ$), adding this $χ^2$ to that of $f_{\mathrm{MCs}}$ gives a combined likelihood of $P = 3.90\times10^{-5}$ ($4.11σ$).

astro-ph.GA↗

arXiv2023

The many tensions with dark-matter based models and implications on the nature of the Universe

(Abridged) Fundamental tensions between observations and dark-matter based cosmological models have emerged. This updated review has two purposes: to explore new tensions that have arisen in recent years, compounding the unresolved tensions from previous studies, and to use the shortcomings of the current theory to guide the development of a successful model. Tensions arise in view of the profusion of thin disk galaxies, the pronounced symmetrical structure of the Local Group of Galaxies, the common occurrence of planes of satellite systems, the El Gordo and Bullet galaxy clusters, significant matter inhomogeneities on scales much larger than 100 Mpc, and the observed rapid formation of galaxies and super-massive black holes at redshifts larger than 7. Given the nature of the tensions, the real Universe needs to be described by a model in which gravitation is effectively stronger than Einsteinian/Newtonian gravitation at accelerations below Milgrom's acceleration scale. The promising nuHDM model, anchored on Milgromian dynamics but keeping the standard expansion history with dark energy, solves many of the above tensions. However galaxy formation appears to occur too late in this model, model galaxy clusters reach too large masses, and the mass function of model galaxy clusters is too flat and thus top-heavy in comparison to the observed mass function. Classes of models that reassess inflation, dark energy and the role of the CMB should be explored.

astro-ph.CO↗

arXiv2021

Barred spiral galaxies in modified gravity theories

When bars form within galaxy formation simulations in the standard cosmological context, dynamical friction with dark matter (DM) causes them to rotate rather slowly. However, almost all observed galactic bars are fast in terms of the ratio between corotation radius and bar length. Here, we explicitly display an $8σ$ tension between the observed distribution of this ratio and that in the EAGLE simulation at redshift 0. We also compare the evolution of Newtonian galactic discs embedded in DM haloes to their evolution in three extended gravity theories: Milgromian Dynamics (MOND), a model of non-local gravity, and a scalar-tensor-vector gravity theory (MOG). Although our models start with the same initial baryonic distribution and rotation curve, the long-term evolution is different. The bar instability happens more violently in MOND compared to the other models. There are some common features between the extended gravity models, in particular the negligible role played by dynamical friction $-$ which plays a key role in the DM model. Partly for this reason, all extended gravity models predict weaker bars and faster bar pattern speeds compared to the DM case. Although the absence of strong bars in our idealized, isolated extended gravity simulations is in tension with observations, they reproduce the strong observational preference for `fast' bar pattern speeds, which we could not do with DM. We confirm previous findings that apparently `ultrafast' bars can be due to bar-spiral arm alignment leading to an overestimated bar length, especially in extended gravity scenarios where the bar is already fast.

astro-ph.GA↗