arXiv subjects

Victor Robles

Publications and source records attributed to Victor Robles.

8 recordsLinked to original sources

arXiv2026

Variability in Supermassive Black-Hole Accretion Rates in Fuzzy Dark Matter Cores due to Black-Hole Wandering

Soliton cores in fuzzy dark matter (FDM) deepen nuclear potentials and have been proposed to strongly boost Bondi accretion, potentially aiding rapid black-hole growth at high redshift. We test this in live Schrodinger-Poisson FDM cores coupled to isothermal gas, evolving a moving black hole that grows via a strictly mass-conserving sink. We measure boosts relative to the initial mean-density Bondi rate. Low-mass seeds, with initial black-hole masses less than about 10^6 solar masses, do not sustain large boosts: black-hole wandering and soliton sloshing drive bursty accretion, with dense gas only intermittently present near the black hole. Intermediate seeds, with initial black-hole masses around 10^7 solar masses, produce the most durable enhancement, reaching boosts of order 100 for sound speed cs = 60 km/s, while hotter gas approaches near-background Bondi rates. High-mass seeds, with initial black-hole masses around 10^8 solar masses, quickly exhaust the sink-scale reservoir and become supply-limited, suppressing long-lived growth despite the deepened potential. In general, central-potential deepening, for example by a soliton halo, does not guarantee long-lived fueling: sustained boosts emerge only when the black hole remains dynamically confined within the dense nuclear gas region. Our results suggest that SMBH formation channels relying on soliton-enhanced accretion alone are unlikely to provide sufficient early growth.

astro-ph.CO↗

arXiv2023

On the Dynamical Heating of Dwarf Galaxies in a Fuzzy Dark Matter Halo

Fuzzy Dark Matter (FDM), consisting of ultralight bosons, is an intriguing alternative to Cold Dark Matter. Numerical simulations solving the Schr\"odinger-Poisson (SP) equation, which governs FDM dynamics, show that FDM halos consist of a central solitonic core (representing the ground state of the SP equation), surrounded by a large envelope of excited states. Wave interference gives rise to order unity density fluctuations throughout the envelope and causes the soliton to undergo density oscillations and execute a confined random walk in the central region of the halo. The resulting gravitational potential perturbations are an efficient source of dynamical heating. Using high-resolution numerical simulations of a $6.6 \times 10^{9} \rm M_{\odot}$ FDM halo with boson mass, $m_{\rm b}=8 \times 10^{-23} \ \rm eV$, we investigate the impact of this dynamical heating on the structure and kinematics of spheroidal dwarf galaxies of a fixed mass but different initial sizes and ellipticities. The galaxies are set up in equilibrium in the time-and-azimuthally averaged halo potential and evolved for $10 \ \rm Gyr$ in the live FDM halo. We find that they continuously increase their sizes and central velocity dispersions. In addition, their kinematic structures become strongly radially anisotropic, especially in the outskirts. Dynamical heating also causes initially ellipsoidal galaxies to become more spherical over time from the inside out and gives rise to distorted, non-concentric isodensity contours. These tell-tale characteristics of dynamical heating of dwarf galaxies in FDM halos can potentially be used to constrain the boson mass.

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arXiv2021

The central densities of Milky Way-mass galaxies in cold and self-interacting dark matter models

We present a suite of baryonic cosmological zoom-in simulations of self-interacting dark matter (SIDM) haloes within the ``Feedback In Realistic Environment'' (FIRE) project. The three simulated haloes have virial masses of $\sim 10^{12}\, \text{M}_\odot$ at $z=0$, and we study velocity-independent self-interaction cross sections of 1 and 10 ${\rm cm^2 \, g^{-1}}$. We study star formation rates and the shape of dark matter density profiles of the parent haloes in both cold dark matter (CDM) and SIDM models. Galaxies formed in the SIDM haloes have higher star formation rates at $z\leq1$, resulting in more massive galaxies compared to the CDM simulations. While both CDM and SIDM simulations show diverse shape of the dark matter density profiles, the SIDM haloes can reach higher and more steep central densities within few kpcs compared to the CDM haloes. We identify a correlation between the build-up of the stars within the half-mass radii of the galaxies and the growth in the central dark matter densities. The thermalization process in the SIDM haloes is enhanced in the presence of a dense stellar component. Hence, SIDM haloes with highly concentrated baryonic profiles are predicted to have higher central dark matter densities than the CDM haloes. Overall, the SIDM haloes are more responsive to the presence of a massive baryonic distribution than their CDM counterparts.

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arXiv2019

First star-forming structures in fuzzy cosmic filaments

In hierarchical models of structure formation, the first galaxies form in low-mass dark matter potential wells, probing the behavior of dark matter on kiloparsec (kpc) scales. Even though these objects are below the detection threshold of current telescopes, future missions will open an observational window into this emergent world. In this Letter we investigate how the first galaxies are assembled in a `fuzzy' dark matter (FDM) cosmology where dark matter is an ultralight $\sim 10^{-22}$~eV boson and the primordial stars are expected to form along dense dark matter filaments. Using a first-of-its-kind cosmological hydrodynamical simulation, we explore the interplay between baryonic physics and unique wavelike features inherent to FDM. In our simulation, the dark matter filaments show coherent interference patterns on the boson de Broglie scale and develop cylindrical soliton-like cores which are unstable under gravity and collapse into kpc-scale spherical solitons. Features of the dark matter distribution are largely unaffected by the baryonic feedback. On the contrary, the distributions of gas and stars, which do form along the entire filament, exhibit central cores imprinted by dark matter -- a smoking gun signature of FDM.

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arXiv2018

Dwarf Galaxies in CDM, WDM, and SIDM: Disentangling Baryons and Dark Matter Physics

We present a suite of FIRE-2 cosmological zoom-in simulations of isolated field dwarf galaxies, all with masses of $M_\mathrm{halo} \approx 10^{10}\,$M$_\odot$ at $z=0$, across a range of dark matter models. For the first time, we compare how both self-interacting dark matter (SIDM) and/or warm dark matter (WDM) models affect the assembly histories as well as the central density structure in fully hydrodynamical simulations of dwarfs. Dwarfs with smaller stellar half-mass radii (r$_{1/2}<500$ pc) have lower $\sigma_\star/V_\mathrm{max}$ ratios, reinforcing the idea that smaller dwarfs may reside in halos that are more massive than is naively expected. The majority of dwarfs simulated with self-interactions actually experience contraction of their inner density profiles with the addition of baryons relative to the cores produced in dark-matter-only runs, though the simulated dwarfs are always less centrally dense than in $\Lambda$CDM. The V$_{1/2}-$r$_{1/2}$ relation across all simulations is generally consistent with observations of Local Field dwarfs, though compact objects such as Tucana provide a unique challenge. Spatially-resolved rotation curves in the central regions ($<400$ pc) of small dwarfs could provide a way to distinguish between CDM, WDM, and SIDM, however: at the masses probed in this simulation suite, cored density profiles in dwarfs with small r$_{1/2}$ values can only originate from dark matter self-interactions.

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arXiv2017

Galaxy Formation with BECDM: I. Turbulence and relaxation of idealised haloes

We present a theoretical analysis of some unexplored aspects of relaxed Bose-Einstein condensate dark matter (BECDM) haloes. This type of ultralight bosonic scalar field dark matter is a viable alternative to the standard cold dark matter (CDM) paradigm, as it makes the same large-scale predictions as CDM and potentially overcomes CDM's small-scale problems via a galaxy-scale de Broglie wavelength. We simulate BECDM halo formation through mergers, evolved under the Schr\"odinger-Poisson equations. The formed haloes consist of a soliton core supported against gravitational collapse by the quantum pressure tensor and an asymptotic $r^{-3}$ NFW-like profile. We find a fundamental relation of the core=to-halo mass with the dimensionless invariant $\Xi \equiv \lvert E \rvert/M^3/(Gm/\hbar)^2$ or $M_{\rm c}/M \simeq 2.6 \Xi^{1/3}$, linking the soliton to global halo properties. For $r \geq 3.5 \,r_{\rm c}$ core radii, we find equipartition between potential, classical kinetic, and quantum gradient energies. The haloes also exhibit a conspicuous turbulent behavior driven by the continuous reconnection of vortex lines due to wave interference. We analyse the turbulence 1D velocity power spectrum and find a $k^{-1.1}$ power-law. This suggests the vorticity in BECDM haloes is homogeneous, similar to thermally-driven counterflow BEC systems from condensed matter physics, in contrast to a $k^{-5/3}$ Kolmogorov power-law seen in mechanically-driven quantum systems. The mode where the power spectrum peaks is approximately the soliton width, implying the soliton-sized granules carry most of the turbulent energy in BECDM haloes.

astro-ph.CO↗

arXiv2013

A Review on the Scalar Field/ Bose-Einstein Condensate Dark Matter Model

We review the work done so far aimed at modeling in an alternative way the dark matter in the Universe: the scalar field/ Bose-Einstein condensate dark matter (SFDM/BEC) model. We discuss a number of important achievements and characteristics of the model. We also describe some of our most recent results and predictions of the model compared to those of the standard model of $\Lambda$CDM.

astro-ph.CO↗

arXiv2012

A brief Review of the Scalar Field Dark Matter model

In the last time the cold dark matter (CDM) model has suggested more and more that it is not able to describe all the properties of nearby galaxies that can be observed in great detail as well as that it has some problems in the mechanism by which matter is more rapidly gathered into large-scale structure such as galaxies and clusters of galaxies. In this work we revisit an alternative model, the scalar field dark matter (SFDM) model, which proposes that the galactic haloes form by condensation of a scalar field (SF) very early in the Universe, i.e., in this model the haloes of galaxies are astronomical Bose-Einstein Condensate drops of SF. On the other hand, large-scale structures like clusters or superclusters of galaxies form similar to the $\Lambda$CDM model, by hierarchy, thus all the predictions of the $\Lambda$CDM model at cosmological scales are reproduced by SFDM. This model predicts that all galaxy haloes must be very similar and exist for higher redshifts than in the $\Lambda$CDM model. In the first part of this review we revisit the cosmological evolution of SFDM model with a scalar potential $m^2\Phi^2/2+\lambda\Phi^4/4$ with two different frameworks: the field and fluid approach. The scalar fluctuations have an oscillating growing mode and therefore, this kind of dark matter could lead to the early formation of gravitational structures in the Universe. In the last part, we study the core central density profiles of BEC dark matter haloes and fit high-resolution rotation curves of low surface brightness galaxies. The mean value of the logarithmic inner density slopes is $\alpha = - $0.27 $\pm$ 0.18 and we show that the recent observation of the constant dark matter central surface density can be reproduced. We conclude that in light of the difficulties that the $\Lambda$CDM model is currently facing the SFDM model can be a worthy alternative to keep exploring further.

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