arXiv subjects

Juan Manuel Pacheco-Arias

Publications and source records attributed to Juan Manuel Pacheco-Arias.

3 recordsLinked to original sources

arXiv2026

IllustrisTNG50 angular momentum maps: tracing the morpho-kinematic evolution of galaxies

Following the first observational study of the two-dimensional spatial distribution of stellar specific angular momentum (sAM) in late-type galaxies, we quantify the morpho-kinematic diversity of galaxy simulations using the newly proposed j-types classification. We analyse the stellar sAM surface density (sAMSD) of $\sim$8000 TNG50 stellar discs spanning $0 \leq z \leq 3.5$ and $9.5 \leq \log(M_\star/\mathrm{M}_\odot) \leq 11.2$, selected from the TNG50 MW/M31 parent sample. We characterize their j-substructures using four morpho-kinematic metrics derived from comparisons with the Freeman sAMSD distribution and the Fourier decomposition of the galaxies in the sAMSD space. A Gaussian mixture model with four fully covariant components assigns each galaxy a probability of belonging to one of four j-types. We find that TNG50 discs exhibit a morpho-kinematic diversity consistent with observations, redistributing stellar angular momentum through four dominant j-substructures that evolve with redshift as follows: j-irregulars ($\bar{z}=0.91$), j-spirals ($\bar{z}=0.76$), j-rings ($\bar{z}=0.62$), and j-bars ($\bar{z}=0.39$). The gas fraction and stellar rotational support ($V/σ$) drive this evolution: gas-rich galaxies preferentially host j-irregulars and j-spirals, whereas gas-poor systems favour j-rings and j-bars. At fixed gas fraction, higher $V/σ$ favours j-spirals and j-rings, respectively. We conclude that there is a canonical pathway for the redistribution of angular momentum within galactic discs undergoing secular evolution in TNG50, accessible only through their morpho-kinematic description. The sAMSD analysis links variations in stellar dynamics to their consequences for mass redistribution, enabling the reconstruction of comprehensive galactic evolutionary histories.

astro-ph.GA↗

arXiv2026

New morpho-kinematic classification: The two-dimensional spatial distribution of stellar specific angular momentum in late-type galaxies

The two-dimensional spatial distribution of stellar specific angular momentum (sAM) within galaxies has never been previously analysed. We investigate its morpho-kinematics and its relation to total stellar sAM (jstar) and stellar mass (Mstar) for 30 spiral and irregular galaxies from the GHASP survey. We constructed high-resolution stellar sAM surface density (sAMSD) maps by combining 3.4 micron WISE photometry with Halpha velocity fields and HI rotation curves. Their structure was quantified using non-parametric morphological indicators (concentration, asymmetry, smoothness) plus two additional coefficients measuring similarity to an axisymmetric Freeman disc and the strength of bisymmetric substructures in sAMSD space. Each galaxy was assigned to one of five new morpho-kinematic classes based on its dominant sAMSD feature: jstar-ring, jstar-spiral, jstar-bar, jstar-clump, and jstar-irregular. This defines a classification scheme that combines directly morphology and dynamics. For 14 galaxies, the classical morphological type differs from the sAMSD-based category. As expected, jstar correlates strongly with Mstar. We also find correlations between jstar and star formation rate, and between jstar and total HI mass. The mean jstar and Mstar for the different jstar types occupy distinct regions along the Fall relation, with significant internal scatter. The link between the two-dimensional sAMSD distribution and global jstar, together with the location of each type in the jstar-Mstar plane, suggests a possible morpho-kinematic evolutionary sequence for late-type galaxies. The mechanisms reshaping galaxies in sAMSD space appear to be related to disc stability: in low-mass systems, angular momentum redistribution may arise from feedback, dynamical friction, shocks, and resonances, whereas in massive spirals it is likely driven by quasi-stationary rotating density waves.

astro-ph.GA↗

arXiv2023

Formation of black holes in the pair-instability mass gap: Hydrodynamical simulations of a head-on massive star collision

The detection of the binary black hole merger GW190521, with primary black hole mass $85^{+21}_{-14}$ ${\rm M}_{\odot}$, proved the existence of black holes in the theoretically predicted pair-instability gap ($\sim60-120 \, {\rm M}_{\odot}$) of their mass spectrum. Some recent studies suggest that such massive black holes could be produced by the collision of an evolved star with a carbon-oxygen core and a main sequence star. Such a post-coalescence star could end its life avoiding the pair-instability regime and with a direct collapse of its very massive envelope. It is still not clear, however, how the collision shapes the structure of the newly produced star and how much mass is actually lost in the impact. We investigated this issue by means of hydrodynamical simulations with the smoothed particle hydrodynamics code {\sc StarSmasher}, finding that a head-on collision can remove up to 12\% of the initial mass of the colliding stars. This is a non-negligible percentage of the initial mass and could affect the further evolution of the stellar remnant, particularly in terms of the final mass of a possibly forming black hole. We also found that the main sequence star can plunge down to the outer boundary of the core of the primary, changing the inner chemical composition of the remnant. The collision expels the outer layers of the primary, leaving a remnant with an helium-enriched envelope (reaching He fractions of about 0.4 at the surface). These more complex abundance profiles can be directly used in stellar evolution simulations of the collision product.

astro-ph.SR↗