arXiv subjects

Andrés Escala

Publications and source records attributed to Andrés Escala.

4 recordsLinked to original sources

arXiv2026

Massive star clusters detected by JWST as natural birth places to form intermediate-mass black holes

The James Webb Space Telescope (JWST) has detected, through gravitational lensing, several young massive star clusters (YMCs), which are considered as relevant building blocks of high redshift galaxies. In this work, we show how a significant fraction of these YMCs could act as relevant birth places for intermediate-mass black holes. We first consider the formation of massive clusters and show that the population of YMCs is consistent with a steep mass-radius relation, which includes a relevant spread of roughly an order of magnitude. We pursue a comparison of this population with young star clusters in the local Universe and Milky Way globular clusters, including an analysis of the characteristic timescales. The YMCs show a wide spread over these properties, but include systems with both short relaxation times as well as relatively short collision timescales, implying they could go through efficient core collapse, which would lead to runaway collisions. We provide quantitative estimates of the sizes of the clusters that could efficiently form intermediate-mass black holes through a runaway collision-based channel, suggesting that these roughly correspond to the systems beyond the $1σ$ scatter in the mass-radius relation. This implies a fraction of ~16% of YMCs as candidates to form intermediate-mass black holes. We show that above a mass limit of ~6x10^6 M_sun, compact star clusters are likely to retain gas even in the presence of strong supernova feedback, altering the dynamics in the central core and providing the possibility to rapidly grow the central object both via gas dynamical friction and Bondi accretion. Finally, we consider the possibility of a gas-dominated regime, in which strong gravitational torques may inhibit star cluster formation and instead directly form a high-mass black holes, as suggested to have occurred in the infinity galaxy.

astro-ph.GA↗

arXiv2021

Black hole fueling in galaxy mergers: A high-resolution analysis

Using parsec scale resolution hydrodynamical adaptive mesh refinement simulations we have studied the mass transport process throughout a galactic merger. The aim of such study is to connect both the peaks of mass accretion rate onto the BHs and star formation bursts with both gravitational and hydrodynamic torques acting on the galactic gaseous component. Our merger initial conditions were chosen to mimic a realistic system. The simulations include gas cooling, star formation, supernovae feedback, and AGN feedback. Gravitational and hydrodynamic torques near pericenter passes trigger gas funneling to the nuclei which is associated with bursts of star formation and black hole growth. Such episodes are intimately related with both kinds of torques acting on the galactic gas. Pericenters trigger both star formation and mass accretion rates of $\sim$ few $(1-10)$ $M_\odot$/yr. Such episodes last $\sim$ $(50-75)$ Myrs. Close passes also can produce black hole accretion that approaches and reaches the Eddington rate, lasting $\sim$ few Myrs. Our simulation shows that both gravitational and hydrodynamic torques are enhanced at pericenter passes with gravitational torques tending to have higher values than the hydrodynamic torques throughout the merger. We also find that in the closest encounters, hydrodynamic and gravitational torques can be comparable in their effect on the gas, the two helping in the redistribution of both angular momentum and mass in the galactic disc. Such phenomena allow inward mass transport onto the BH influence radius, fueling the compact object and lighting up the galactic nuclei.

astro-ph.GA↗

arXiv2019

The role of gas fragmentation during the formation of supermassive black holes

We have performed cosmological hydrodynamic simulations to study the effect of fragmentation on the SMBH seed mass in the direct collapse formation scenario. We considered different background UV intensities, host halo spin, and halo merger histories. Our simulations in low-spin halos, in the presence of a strong UV background are consistent with the Direct Collapse Black Hole model, in which a single massive object $\sim10^5$ M$_{\odot}$ is formed in the center of a proto-galaxy. While in our simulations under the presence of a low UV background, we find fragmentation and the formation of various minor seeds. These fragments have masses of 10$^3$ - 10$^4$ M$_{\odot}$. These values are significant if we consider the potential mergers between them, and the fact that these minor objects are formed earlier in cosmic time compared to the massive single seeds. In one of our simulations, we observed gas fragmentation even in the presence of a strong UV intensity. Said structure arose in a dark matter halo that formed after various merger episodes, and the one with the highest spin value. The final mass obtained was $\sim 10^5$ M$_{\odot}$ in this run. From these results, we conclude that fragmentation in fact produces less massive objects, however, they are still prone to merge. In simulations that formed many fragments, they all approach the most massive one with time. We see no uniqueness in the strength of the UV intensity value required to achieve a DCBH, since it depends in other factors like the system dynamics in our cases.

astro-ph.GA↗

arXiv2016

Unveiling the role of galactic rotation on star formation

We study the star formation process at galactic scales and the role of rotation through numerical simulations of spiral and starburst galaxies using the adaptive mesh refinement code Enzo. We focus on the study of three integrated star formation laws found in the literature: the Kennicutt-Schmidt (KS) and Silk-Elmegreen (SE) laws, and the dimensionally homogeneous equation proposed by Escala (2015) $Σ_{\rm SFR} \propto \sqrt{G/L}Σ_{\rm gas}^{1.5}$. We show that using the last we take into account the effects of the integration along the line of sight and find a unique regime of star formation for both types of galaxies, suppressing the observed bi-modality of the KS law. We find that the efficiencies displayed by our simulations are anti-correlated with the angular velocity of the disk $Ω$ for the three laws studied in this work. Finally, we show that the dimensionless efficiency of star formation is well represented by an exponentially decreasing function of $-1.9Ωt_{\rm ff}^{\rm ini}$, where $t_{\rm ff}^{\rm ini}$ is the initial free-fall time. This leads to a unique galactic star formation relation which reduces the scatter of the bi-modal KS, SE, and Escala (2015) relations by 43%, 43%, and 35% respectively.

astro-ph.GA↗