arXiv subjects

Manuel Zamora-Avilés

Publications and source records attributed to Manuel Zamora-Avilés.

At least 19 recordsLinked to original sources

arXiv2026

Bridging the gap between stars and planets

The formation mechanisms of brown dwarfs (BDs) and free-floating planets (FFPs) are poorly constrained. The two main competing scenarios include the star-like scenario, where these objects correspond to the least massive gravitationally unstable fragments of molecular clouds, and the planet-like scenario, where these objects form in a circumstellar disk and are subsequently ejected after a dynamical interaction. A new generation millimeter interferometer, such as ALMA2040, is required to disentangle the relevance of these scenarios. For this, ALMA2040 must provide the appropriate performance to explore BD/FFP formation from the cloud scale (~10 pc) down to the disk scale (~10 au). At cloud scales, ALMA2040 must detect a ~1 Mjup embedded FFP in the outer Galaxy (~10 kpc) in 1 h, or the same object in nearby clouds (<~ 400 pc) in about tens of seconds so that large-scale surveys of entire clouds can be performed. This would provide key censuses to compare the results with the predictions from each scenario. At disk scales, ALMA2040 must detect CO outflows from first hydrostatic cores in the substellar regime and potential molecular outflows from ~1 Mjup FFPs in nearby clouds, both with specific predictions in the star-like scenario. In addition, the planet-like scenario predicts a disk mass-to-star mass ratio for BDs larger than the star-like case, and testing this requires detecting disks of ~2 Earth masses around young BDs. Furthermore, the predicted emission for the star-like case of complex organic molecules in proto-BDs at 400 pc must be detected with ALMA2040, requiring a factor of 10 increase in line sensitivity at a spatial resolution of 5-10 au. Finally, ALMA2040 must detect Earth-like protoplanets around young BDs at 400 pc, in order to provide key observational constraints on the radial drift behaviour and planet formation mechanisms in the substellar regime.

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arXiv2026

Synthetic polarization observations of magnetized pillars in HII regions: Assessing the reliability of the Davis-Chandrasekhar-Fermi method

We investigated the morphology and strength of magnetic fields in pillar-shaped structures at the boundaries of HII regions by combining three-dimensional radiation-magnetohydrodynamic (R-MHD) simulations with synthetic polarimetric and molecular-line observations. Our analysis focuses on a self-consistently formed pillar as a proof of concept to test the Davis-Chandrasekhar-Fermi (DCF) method under externally driven conditions. The pillar arises as an ionization front compresses a dense clump, producing a magnetically aligned, elongated structure whose morphology and field configuration resemble systems such as the pillars in M16. Synthetic 850 μm dust-polarization maps reproduce the pillar's large-scale magnetic-field morphology, confirming polarimetry as a reliable tracer of magnetic-field geometry. To evaluate DCF-based methods, we extract local density and velocity dispersion self-consistently from synthetic 13CO observations and measure polarization-angle dispersion using single-Gaussian fits to the synthetic polarization-angle distributions. We find that DCF-based methods systematically overestimate the intrinsic plane-of-sky magnetic-field strength by average factors of ~7 for the classical DCF method and ~5 for the modified Skalidis & Tassis formulation. This overestimation is already present in the full-pillar measurement and is not removed by applying polarimetric S/N cuts or by excluding the dynamically complex head. We attribute the discrepancy to external compression by the expanding H II region, which organizes the magnetic field on pillar scales while driving non-thermal gas motions. Consequently, the measured velocity and polarization-angle dispersions no longer trace the same turbulence-driven perturbation field assumed by DCF. Our results highlight the need for caution when applying DCF-based analyses to pillars or other externally compressed structures.

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arXiv2026

The efficiency per free-fall time as a ratio of the Star Formation Rate to the gas-infall rate in collapsing cores: dependence on the core definition, accretion, and radial structure

A parameter used to characterise star formation activity in MCs is the efficiency per free-fall time, $ε_{\rm ff}$, although commonly referred to as an efficiency, it is formally the ratio between the star formation rate (SFR) and the gas-infall rate. Here we numerically study the collapse of cores and define $ε_{\rm ff}\equiv\langle\dot{M}_\star\rangle/(M_{\rm core}/τ_{\rm ff})$, where $\langle\dot{M}_\star\rangle$ is the average SFR, $M_{\rm core}$ is the gas mass within the core (as the gas cells above a density threshold), and $τ_{\rm ff}$ is the free-fall time of the core gas. We perform simplified numerical experiments of the gravitational collapse of an isolated core, varying the initial mean number density ($n_0=100$ and $1000~\rm cm^{-3}$) and adopting closed/open BCs to (dis)allow fresh gas accretion into the domain. The simulations start with a slight central Gaussian overdensity that evolved into a power-law profile, $n\propto r^{-p}$ with $p\to2$. As the collapse proceeds, a sink particle forms in the center of the core. We find that both the BCs and the adopted core definition modify the measured core properties and, consequently, the inferred $ε_{\rm ff}$. Low-density models have less mass available, and their accretion histories are therefore much more sensitive to the choice of BCs, while high-density runs, with their larger mass reservoirs, maintain similar accretion histories regardless of the BCs. In all models, after sink formation, $ε_{\rm ff}$ rises and then remains relatively stable while accretion continues to replenish the core's mass, but increases once the gas reservoir is exhausted. Somewhat counterintuitively, $ε_{\rm ff}$ is higher in the low-mass cores, since the larger gas infall rates onto the high-mass cores compensate for their higher SFR. We conclude that the inferred $ε_{\rm ff}$ depends sensitively on both the adopted core definition and external mass supply

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arXiv2026

Comparing the $M_{gas}-N_{yso}$ Relation inside a Giant Molecular Cloud

In this paper we present a simple analysis around scaling relations derived from the Schmidt conjecture for star-forming molecular clouds, at the intra-cloud scale. Using a hierarchical tree (dendrograms) above a constant threshold ($A_V$ = 7 mag), we separate individual gas structures in a column density map of the nearby Giant Molecular Cloud Orion A, constructed from Herschel far-infrared maps. These structures define regions of dense molecular gas that can actively form stars. We also estimate their current embedded population using a list of known young stars. From the combined analysis of the column density map and the young star catalog, we construct a series of plots that show the intra-cloud level behavior of three well-known scaling relations: $N_{yso}$ vs. $M_{gas}$, $Σ_{SFR}$ vs. $Σ_{gas}$ and $R_{eq}$ vs. $M_{gas}$. Our dataset, along with other sets from literature, show the validity of a linear relation for $N_{yso}$ vs. $M_{gas}$, from intra-cloud to inter-cloud scales, over three orders of magnitude. We also especulate on the possibility that the relation could be valid over an even larger scale range. Additionally, our data are consistent with the $R_{eq}$ vs. $M_{gas}$ discussed in previous studies. However, our data is not quite in agreement with previously proposed fits for the $Σ_{SFR}$ vs. $Σ_{gas}$ relation, and we discuss the implications of using the free-fall timescale as the main parameter defining the star-forming efficiency in dense gas regions.

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arXiv2025

Peculiar galaxies I: A Catalog of Polar-Ring Galaxies from the TNG50 Simulation

The hydrodynamic cosmological simulation, TNG50, is employed to conduct an analysis of multi-spin galaxies that exhibit ringed structures composed of gas and stars that orbit nearly perpendicular around a host galaxy, known as polar ring galaxies (PRG). To ensure a robust sample, we select subhalos based on the angle subtended by the angular momentum profiles, as well as on a visual inspection. The analysis is focused on galaxies with stellar masses greater than 10$^{9}$ M$_\odot$. In addition, a dynamic decomposition is employed to separate the stellar and gaseous ring from the host galaxy. This results in a sample of 32 subhalos with PRGs. This sample exhibits properties similar to those observed. These include colours typical of early-type galaxies (ETGs) or those transitioning toward blue systems. Most host galaxies are classified as ETGs, with 37.5\% exhibiting a disk-dominated morphology. The mean bulge-to-total (B/T) ratio is 0.64. Rings have average radii that are 2.36 and 3.41 times larger than their effective radii for the stellar and gaseous components, respectively, with star formation occurring predominantly within the rings. In contrast with observations, rings in the simulation tend to be less massive and slightly less perpendicular. The obtained sample displays a variety of host galaxy morphologies, including wide and narrow rings, providing a robust framework for studying the varied structural characteristics of PRG variants.

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arXiv2025

The Turbulent Support (TS) and Global Hierarchical Collapse (GHC) models for molecular clouds compared. Differences, convergence, and myths

We provide a detailed comparison between the ``turbulent support'' (TS) and ``global hierarchical collapse'' (GHC) models for molecular clouds and star formation, their respective interpretations of the observational data, the features they share, and suggested tests and observations to discern between them. Also, we clarify common misconceptions in recent literature about the global and hierarchical nature of the GHC scenario, and briefly discuss the evolution of some aspects of both models toward convergence. TS assumes that star-forming molecular clouds and their substructures are either in approximate virial equilibrium between gravity and turbulence or overvirial, so that the cloud is either confined or expanding, and its substructures (clumps, filaments and cores) are produced by turbulent compressions. In this scheme, the star formation rate (SFR) is time-independent and determined by the turbulent and gravitational parameters of the clouds, in particular the virial parameter $\av$. Conversely, GHC assumes that most star-forming molecular clouds and their substructures are part of a continuous gravitationally-driven flow, each accreting from their parent structure. Therefore, GHC is an intrinsically {\it evolutionary} model for the clouds and their star formation rate, determined by the evolution of the collapse flow. It interprets nonthermal motions as a mixture of infall and turbulent components, with the relative importance of the former increasing as the objects become denser and/or more massive, and thus $\av$ is an {\it evolving variable} of the clouds. Tests that may provide clues to distinguishing between TS and GHC must take into account that the innermost parts of globally gravitationally bound structures may not locally appear bound, and thus the binding may have to be searched for at the largest scale of the structure.

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arXiv2024

Gravity or turbulence? VI. The physics behind the Kennicutt-Schmidt relations

We explain the large variety of star formation laws in terms of one single, simple law that can be inferred from the definition of the star formation rate and basic algebra. The resulting equation, $\SFR = \eff\ \Mcollapsing/\tauff$, although it has been presented elsewhere, is interpreted in terms of clouds undergoing collapse { rather than being turbulence-supported, an idea that different groups have pursued this century}. Under such assumption, one can explain the constancy of $\eff$, the different intra-cloud correlations observed in Milky Way's molecular clouds, as well as the resolved and unresolved extragalactic relationships between SFR and a measurement of the mass in CO, HCN, and CO+HI. We also explain why the slope of the correlation changes when the orbital time $\tauorb$ is considered instead of the free-fall time, and why estimations of the free-fall time from extragalactic observations skew the correlation, providing a false sublinear correlation. We furthermore show that the apparent nearly linear correlation between the star formation rate and the dynamical equilibrium pressure in the midplane of the galaxies, $\PDE$, is just a consequence of $\PDE$ values being dominated by the variation of the column density of molecular gas. All in all, we argue that the star formation law is driven by the collapse of cold, dense gas, which happens to be primarily molecular in the present Universe, and that the role of stellar feedback is just to shut down the star formation process, not to shape the star formation law.

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arXiv2023

The kinetic and magnetic energy budget of hub-filament systems during the gravitational fragmentation of molecular clouds

We present a numerical study of the balance between the gravitational (Eg), kinetic (Ek), and magnetic (Em) energies of structures within a hub-filament system in a simulation of the formation and global hierarchical collapse (GHC) of a giant molecular cloud. For structures defined by various density thresholds, and at different evolutionary stages, we investigate the scaling of the virial parameter, $α$, with mass $M$, and of the Larson ratio, ${\cal{L}}\equivσ_v/R^{1/2}$, with column density $Σ$, where $σ_v$ is the 1D velocity dispersion, and $R$ is an effective radius. We also investigate these scalings for the corresponding magnetic parameters $α_m$ and ${\cal{L}}_m$. Finally, we compare our numerical results with an observational sample of massive clumps. We find that: 1) $α_m$ and ${\cal{L}}_m$ follow similar scalings as their kinetic counterparts, although the ratio Em/Ek decreases as |Eg| increases. 2) The largest objects, defined by the lowest thresholds, tend to appear gravitationally bound (and magnetically supercritical), while their internal substructures tend to appear unbound (and subcritical). This suggests that the latter are being compressed by the infall of their parent structures, and supports earlier suggestions that the measured mass-to-magnetic flux ratio $μ$ decreases inwards in a centrally-peaked cloud under ideal MHD. 3)~The scatter in the $α$-$M$ and ${\cal{L}}$-$Σ$ plots is reduced when Ek and Em are plotted directly against Eg, suggesting that the scatter is due to an ambiguity between mass and size. 4) The clumps in our GHC simulation follow the same trends as the observational sample of massive clumps in the $α$-$M$ and ${\cal{L}}$-$Σ$ diagrams. We conclude that the main controlling parameter of the energy budget in the structures is Eg, with the kinetic and magnetic energies being derived from it.

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arXiv2023

Simulated observations of star formation regions: infrared evolution of globally collapsing clouds

The direct comparison between hydrodynamical simulations and observations is needed to improve the physics included in the former and test biases in the latter. Post-processing radiative transfer and synthetic observations are now the standard way to do this. We report on the first application of the \texttt{SKIRT} radiative transfer code to simulations of a star-forming cloud. The synthetic observations are then analyzed following traditional observational workflows. We find that in the early stages of the simulation, stellar radiation is inefficient in heating dust to the temperatures observed in Galactic clouds, thus the addition of an interstellar radiation field is necessary. The spectral energy distribution of the cloud settles rather quickly after $\sim3$ Myr of evolution from the onset of star formation, but its morphology continues to evolve for $\sim8$ Myr due to the expansion of \textsc{Hii} regions and the respective creation of cavities, filaments, and ridges. Modeling synthetic \textit{Herschel} fluxes with 1- or 2-component modified black bodies underestimates total dust masses by a factor of $\sim2$. Spatially-resolved fitting recovers up to about $70\%$ of the intrinsic value. This ``missing mass'' is located in a very cold dust component with temperatures below $10$ K, which does not contribute appreciably to the far-infrared flux. This effect could bias real observations if such dust exists in large amounts. Finally, we tested observational calibrations of the SFR based on infrared fluxes and concluded that they are in agreement when compared to the intrinsic SFR of the simulation averaged over $\sim100$ Myr.

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arXiv2022

A resolution criterion based on characteristic timescales for MHD simulations of molecular clouds

We investigate the effect of numerical magnetic diffusion in magnetohydrodynamic simulations of magnetically supported molecular clouds. To this end, we have performed numerical studies on adaptive mesh isothermal simulations of marginally sub-critical molecular clouds. We find that simulations with low and intermediate resolutions collapse, contrary to what is theoretically expected. However, the simulation with the highest numerical resolution oscillates around an equilibrium state without collapsing. In order to quantify the numerical diffusion of the magnetic field, we ran a second suit of current-sheet simulations in which the numerical magnetic diffusion coefficient can be directly measured, and computed the corresponding diffusion times at various numerical resolutions. On this basis, we propose a criterion for the resolution of magnetic fields in MHD simulations based on requiring that the diffusion time to be larger than the characteristic timescale of the physical process responsible for the dynamic evolution of the structure.

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arXiv2020

Simultaneous evolution of the virial parameter and star formation rate in molecular clumps undergoing global hierarchical collapse

We compare dense clumps and cores in a numerical simulation of molecular clouds (MCs) undergoing global hierarchical collapse (GHC) to observations in two MCs at different evolutionary stages, the Pipe and the G14.225 clouds, to test the ability of the GHC scenario to follow the early evolution of the energy budget and star formation activity of these structures. In the simulation, we select a region that contains cores of sizes and densities similar to the Pipe cores, and find that it evolves through accretion, developing substructure similar to that of G14.225 cloud after $\sim 1.6$ Myr. Within this region, we follow the evolution of the Larson ratio $\mathcal{L} \equiv σ_{\rm v}/R^{1/2}$, where $σ_{\rm v}$ is the velocity dispersion and $R$ is the size, the virial parameter $α$, and the star formation activity of the cores/clumps. In the simulation, we find that as the region evolves: $i)$ its clumps have $\mathcal{L}$ and $α$ values first consistent with those of the Pipe substructures and later with those of G14.225; $ii)$ the individual cores first exhibit a decrease in $α$ followed by an increase when star formation begins; $iii)$ collectively, the ensemble of cores/clumps reproduces the observed trend of lower $α$ for higher-mass objects, and $iv)$ the star formation rate and star formation efficiency increase monotonically. We suggest that this evolution is due to the simultaneous loss of externally-driven compressive kinetic energy and increase of the self-gravity-driven motions. We conclude that the GHC scenario provides a realistic description of the evolution of the energy budget of the clouds' substructure at early times, which occurs simultaneously with an evolution of the star formation activity.

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arXiv2019

Global Hierarchical Collapse In Molecular Clouds. Towards a Comprehensive Scenario

We present a unified description of the scenario of Global Hierarchical Collapse and fragmentation (GHC) in molecular clouds (MCs), owing to the continuous decrease of the average Jeans mass in the contracting cloud. GHC constitutes a regime of collapses within collapses, in which small-scale collapses begin at later times, but occur on shorter timescales than large-scale ones. The difference in timescales allows for most of the clouds' mass to be dispersed by feedback from the first massive stars, maintaining the global star formation rate low. All scales accrete from their parent structures. The main features of GHC are: star-forming MCs are in an essentially pressureless regime, which produces filaments that accrete onto clumps and cores ("hubs"). The filaments constitute the collapse flow from cloud to hub scales and may approach a quasi-stationary state; the molecular and dense mass fractions of the clouds increase over time; the first (low-mass) stars appear several Myr after global contraction began; more massive stars appear after a few Myr in massive hubs resulting from the collapse of larger scales; the minimum fragment mass may extend well into the brown-dwarf regime; Bondi-Hoyle-Lyttleton accretion occurs at the protostellar and core scales, accounting for a near-Salpeter IMF; the extreme anisotropy of the filamentary network explains the difficulty in detecting large-scale infall signatures; the balance between inertial and gravitationally-driven motions in clumps evolves during the contraction; prestellar cores adopt Bonnor-Ebert-like profiles, but are contracting ever since early times when they may appear to be unbound and to require pressure confinement; stellar clusters develop radial age and mass segregation gradients. Finally, we discuss the incompatibility between supersonic turbulence and the observed scalings in the molecular hierarchy.

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arXiv2019

What is the physics behind the Larson mass-size relation?

Different studies have reported a power-law mass-size relation $M \propto R^q$ for ensembles of molecular clouds. In the case of nearby clouds, the index of the power-law $q$ is close to 2. However, for clouds spread all over the Galaxy, indexes larger than 2 are reported. We show that indexes larger than 2 could be the result of line-of-sight superposition of emission that does not belong to the cloud itself. We found that a random factor of gas contamination, between 0.001\%\ and 10\%\ of the line-of-sight, allows to reproduce the mass-size relation with $q \sim 2.2-2.3$ observed in Galactic CO surveys. Furthermore, for dense cores within a single cloud, or molecular clouds within a single galaxy, we argue that, even in these cases, there is observational and theoretical evidence that some degree of superposition may be occurring. However, additional effects may be present in each case, and are briefly discussed. We also argue that defining the fractal dimension of clouds via the mass-size relation is not adequate, since the mass is not {necessarily} a proxy to the area, and the size reported in $M-R$ relations is typically obtained from the square root of the area, rather than from an estimation of the size independent from the area. Finally, we argue that the statistical analysis of finding clouds satisfying the Larson's relations does not mean that each individual cloud is in virial equilibrium.

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arXiv2019

Molecular Cloud Evolution VI. Measuring cloud ages

In previous contributions, we have presented an analytical model describing the evolution of molecular clouds (MCs) undergoing hierarchical gravitational contraction. The cloud's evolution is characterized by an initial increase in its mass, density, and star formation rate (SFR) and efficiency (SFE) as it contracts, followed by a decrease of these quantities as newly formed massive stars begin to disrupt the cloud. The main parameter of the model is the maximum mass reached by the cloud during its evolution. Thus, specifying the instantaneous mass and some other variable completely determines the cloud's evolutionary stage. We apply the model to interpret the observed scatter in SFEs of the cloud sample compiled by Lada et al.\ as an evolutionary effect so that, although clouds such as California and Orion A have similar masses, they are in very different evolutionary stages, causing their very different observed SFRs and SFEs. The model predicts that the California cloud will eventually reach a significantly larger total mass than the Orion A cloud. Next, we apply the model to derive estimated ages of the clouds since the time when approximately 25\% of their mass had become molecular. We find ages from $\sim 1.5$ to 27 Myr, with the most inactive clouds being the youngest. Further predictions of the model are that clouds with very low SFEs should have massive atomic envelopes constituting the majority of their gravitational mass, and that low-mass clouds ($M \sim 10^3$-$10^4 \, M_\odot$) end their lives with a mini-burst of star formation, reaching SFRs $\sim 300$-$500\, M_\odot$ Myr$^{-1}$. By this time, they have contracted to become compact ($\sim 1$ pc) massive star-forming clumps, in general embedded within larger GMCs.

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arXiv2019

Flipping-up the field: gravitational feedback as a mechanism for young clusters dispersal

Recent analyses of Gaia data have provided direct evidence that most young stellar clusters are in a state of expansion, with velocities of the order of ~0.5 km/s. Traditionally, expanding young clusters have been pictured as entities that became unbound due to the lack of gravitational binding once the gas from the parental cloud that formed the cluster has been expelled by the stellar radiation of the massive stars in the cluster. In the present contribution, we used radiation-magnetohydrodynamic numerical simulations of molecular cloud formation and evolution to understand how stellar clusters form and disperse. We found that the ionising feedback from the newborn massive stars expels the gas from the collapse centre, flipping-up the gravitational potential as a consequence of the mass removal from the inside-out. Since neither the parental clouds nor the formed shells are distributed symmetrically around the HII region, net forces pulling out the stars are present, accelerating them towards the edges of the cavity. We call this mechanism ``gravitational feedback", in which the gravity from the expelled gas appears to be the crucial mechanism producing unbound clusters that expand away from their formation centre in an accelerated way in young stellar clusters. This mechanism naturally explains the "Hubble flow-like" expansion observed in several young clusters.

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arXiv2019

Structure and Expansion Law of HII Regions in structured Molecular Clouds

We present radiation-magnetohydrodynamic simulations aimed at studying evolutionary properties of H\,{\normalsize II} regions in turbulent, magnetised, and collapsing molecular clouds formed by converging flows in the warm neutral medium. We focus on the structure, dynamics and expansion laws of these regions. Once a massive star forms in our highly structured clouds, its ionising radiation eventually stops the accretion (through filaments) toward the massive star-forming regions. The new over-pressured H\,{\normalsize II} regions push away the dense gas, thus disrupting the more massive collapse centres. Also, because of the complex density structure in the cloud, the H\,{\normalsize II} regions expand in a hybrid manner: they virtually do not expand toward the densest regions (cores), while they expand according to the classical analytical result towards the rest of the cloud, and in an accelerated way, as a blister region, towards the diffuse medium. Thus, the ionised regions grow anisotropically, and the ionising stars generally appear off-centre of the regions. Finally, we find that the hypotheses assumed in standard H\,{\normalsize II}-region expansion models (fully embedded region, blister-type, or expansion in a density gradient) apply simultaneously in different parts of our simulated H\,{\normalsize II} regions, producing a net expansion law ($R \propto t^α$, with $α$ in the range of 0.93-1.47 and a mean value of $1.2 \pm 0.17$) that differs from any of those of the standard models.

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arXiv2017

Are fibres in molecular cloud filaments real objects?

We analyse the morphology and kinematics of dense filamentary structures produced in a numerical simulation of a star--forming cloud of $1.4 \times 10^4 \, \Msun$ evolving under their own self--gravity in a magnetized medium. This study is motivated by recent observations of velocity--coherent substructures ("fibres") in star-forming filaments. We find such "fibres" ubiquitously in our simulated filament. We found that a fibre in one projection is not necessarily a fibre in another projection, and thus, caution should be taken into account when considering them as real objects. We found that only the densest parts of the filament ($\sim$30\% of the densest volume, which contains $\sim$70\% of the mass) belong to fibres in 2 projections. Moreover, it is quite common that they are formed by separated density enhancements superposed along the line of sight. Observations of fibres can yield insight into the level of turbulent substructure driven by gravity, but care should be taken in interpreting the results given the problem of line of sight superposition. We also studied the morphology and kinematics of the 3D skeleton (spine), finding that subfilaments accrete structured material mainly along the magnetic field lines, which are preferentially perpendicular to the skeleton. The magnetic field is at the same time dragged by the velocity field due to the gravitational collapse.

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arXiv2017

Magnetized converging flows towards the hot core in the intermediate/high-mass star-forming region NGC 6334 V

We present Submillimeter Array (SMA) observations at 345 GHz towards the intermediate/high-mass cluster-forming region NGC 6334 V. From the dust emission we spatially resolve three dense condensations, the brightest one presenting the typical chemistry of a hot core. The magnetic field (derived from the dust polarized emission) shows a bimodal converging pattern towards the hot core. The molecular emission traces two filamentary structures at two different velocities, separated by 2 km/s, converging to the hot core and following the magnetic field distribution. We compare the velocity field and the magnetic field derived from the SMA observations with MHD simulations of star-forming regions dominated by gravity. This comparison allows us to show how the gas falls in from the larger-scale extended dense core (~0.1 pc) of NGC 6334 V towards the higher-density hot core region (~0.02 pc) through two distinctive converging flows dragging the magnetic field, whose strength seems to have been overcome by gravity.

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