arXiv subjects

Anaëlle Maury

Publications and source records attributed to Anaëlle Maury.

11 recordsLinked to original sources

arXiv2026

Magnetic threads and gravity: ALMA Observations of IRDC G14.225-0.506

During the star formation process, the interplay between gravity, turbulence, and B-fields is significant, with B-fields apparently serving a regulatory function. However, the extent to which B-fields are decisive relative to turbulence and gravity remains uncertain. This study aims to ascertain the role of B-fields in the fragmentation of molecular clouds. We examine the B-field observed with ALMA at core scales towards the infrared dark cloud G14.225-0.506, focusing on 3 regions with shared physical conditions, and juxtapose it with prior observations at the Hub-filament system scale. Our findings indicate a similar B-field strength and fragmentation level between the 2 hubs. However, distinct B-field morphologies are identified across the 3 regions where polarized emission is detected. In the region N, the large-scale B-field, which is perpendicular to the filamentary structure, persists at smaller scales in the southern half but becomes distorted near the more massive condensations in the northern half. Notably, these condensations exhibit signs of impending collapse, as evidenced by supercritical mass-to-flux values. In the region S, the B-field is considerably inhomogeneous among the detected condensations, and we do not observe a direct correlation between the field morphology and the condensation density. Lastly, in an isolated dust clump located within a southern filament of the northern hub, the B-field aligns parallel to the elongated emission, suggesting a transition in the field geometry. The B-field shows a clear evolution with spatial scales. We propose that the most massive condensations detected in the northern Hub are undergoing gravitational collapse, as revealed by the relative significance of the magnetic field and gravitational potential and mass-to-flux ratio. The distortion of the B-field could be a response to the flow of material due to the collapse.

astro-ph.GA↗

arXiv2026

On the 3D time evolution of the dust size distribution in protostellar envelopes

Dust plays a fundamental role during protostellar collapse, disk and planet formation. Recent observations suggest that efficient dust growth may begin early, in the protostellar envelopes, potentially even before the formation of the disk. Three-dimensional models of protostellar evolution, addressing multi-size dust growth, gas and dust dynamics and magnetohydrodynamics, are required to characterize the dust evolution in the embedded stages of star formation. We aim to establish a new framework for dust evolution models, following in 3D the dust size distribution both in time and space, in MHD models describing the formation and evolution of star-disk systems, at low numerical cost. We present our work coupling the COALA dust evolution module into the code RAMSES, performing the first 3D MHD simulation of protostellar collapse including simultaneously polydisperse dust growth modeled by the Smoluchowski equation as well as dust dynamics in the terminal velocity approximation. Ice-coated micron-sized grains can rapidly grow in the envelope and survive by not entering the fragmentation regime. The evolution of the dust size distribution is highly anisotropic due to the turbulent nature of the collapse and the development of favorable locations such as outflow cavity walls, which enhance locally the dust-to-gas ratio. We analyzed the first 3D non-ideal MHD simulations that self-consistently account for the dust dynamics and growth during the protostellar stage. Very early in the lifetime of a young embedded protostar, micron-sized grains can grow, and locally the dust size distribution deviates significantly from the MRN initial shape. This new numerical method opens the perspective to treat simultaneously gas/dust dynamics and dust growth in 3D simulations at a low numerical cost for several astrophysical environments.

astro-ph.SR↗

arXiv2026

Dissecting the dust distribution and polarization around two B213 young stellar objects with ALMA

The earliest stages of disk formation and dust evolution during the protostellar phase remain poorly constrained. Millimeter dust emission and its polarization provide key insights into the physical processes and material distribution at the envelope-disk interface. We present ALMA polarimetric observations at 1.4 mm and 3 mm of two young stellar objects in Taurus, IRAS 04166+2706 (K04166) and IRAS 04169+2702 (K04169), probing scales from 25 au to 3000 au. We model the Stokes I emission to separate disk and envelope contributions and analyze the polarization properties to identify the dominant polarization mechanisms. K04166 shows extended Stokes I and polarized emission tracing a tentative hourglass magnetic field morphology in its envelope. In the inner envelope and disk (< 100 au), the properties of the polarized emission change, suggesting either a toroidal magnetic field or the presence of large grains. In contrast, K04169 exhibits compact Stokes I and polarized emission consistent with self-scattering from the disk. Both disks are extremely compact, but only K04166 retains a substantial envelope. Our multiscale ALMA polarimetric observations reveal a transition from magnetically aligned grains in envelopes to self-scattering in disks within the transition region of 20-50 au. These results provide important clues on dust grain growth and magnetic field morphology at the disk-envelope scales. Despite being embedded in the same filament, the two sources display striking differences, indicating that K04166 is a young embedded object with a substantial envelope threaded by relatively organized magnetic fields. Meanwhile, K04169 is more evolved, likely to be a young T-Tauri star. However, in both disks, the presence of large grains already suggests a scenario of early dust evolution in disks of the Class 0 stage.

astro-ph.SR↗

arXiv2024

Accuracy of ALMA estimates of young disk radii and masses. Predicted observations from numerical simulations

Protoplanetary disks, which are the natural consequence of the gravitational collapse of the dense molecular cloud cores, host the formation of the known planetary systems in our universe. Substantial efforts have been dedicated to investigating the properties of these disks in the more mature Class II stage, either via numerical simulations of disk evolution from a limited range of initial conditions or observations of their dust continuum and line emission from specific molecular tracers. The results coming from these two standpoints have been used to draw comparisons. However, few studies have investigated the main limitations at work when measuring the embedded Class 0/I disk properties from observations, especially in a statistical fashion. In this study, we provide a first attempt to compare the accuracy of some critical disk parameters in Class 0/I systems, as derived on real ALMA observational data, with the corresponding physical parameters that can be directly defined by theoreticians and modellers in numerical simulations. The approach we follow here is to provide full post-processing of the numerical simulations and apply it to the synthetic observations the same techniques used by observers to derive the physical parameters. We performed 3D Monte Carlo radiative transfer and mock interferometric observations of the disk populations formed in a magnetohydrodynamic (MHD) simulation model of disk formation through the collapse of massive clumps with the tools \textsc{Radmc-3d} and \textsc{Casa}, respectively, to obtain their synthetic observations. With these observations, we re-employed the techniques commonly used in disk modelling from their continuum emissions to infer the properties that would most likely be obtained with real interferometers. We then demonstrated how these properties may vary with respect to the gas kinematics analyses and dust continuum modelling.

astro-ph.EP↗

arXiv2022

The role of magnetic fields in the formation of protostars, disks, and outflows

We present our current understanding of the formation and early evolution of protostars, protoplanetary disks, and the driving of outflows as dictated by the interplay of magnetic fields and partially ionized gas in molecular cloud cores. In recent years, the field has witnessed enormous development through sub-millimeter observations which in turn have constrained models of protostar formation. As a result of these observations % that the observations provided, the state-of-the-art theoretical understanding of the formation and evolution of young stellar objects is described. In particular, we emphasize the importance of the coupling, decoupling, and re-coupling between weakly ionized gas and the magnetic field on appropriate scales. This highlights the complex and intimate relationship between gravitational collapse and magnetic fields in young protostars.

astro-ph.SR↗

arXiv2022

Is the mm/submm dust polarization a robust tracer of the magnetic field topology in protostellar envelopes? A model exploration

High resolution (sub-)millimeter polarization observations have opened a new era in the understanding of how B-fields are organized in star forming regions, unveiling an intricate interplay between the B-fields and the gas in protostellar cores. However, to assess the role of the B-field in the process of solar-type star formation, it is key to be able to understand to what extent these polarized dust emissions are good tracers of the B-field in the youngest protostellar objects. We present a thorough investigation of the fidelity and limitations of using dust polarized emission to map the B-field topologies in low-mass protostars. To assess the importance of these effects, we performed the analysis of B-field properties in 27 realizations of MHD models of star-forming cores. Assuming a uniform population of dust grains whose sizes follow the standard MRN, we analyze the synthetic polarized dust emission maps produced if these grains align with the local B-field thanks to B-RATs. We find that (sub-)millimeter polarized dust emission is a robust tracer of the B-field topologies in inner protostellar envelopes and is successful at capturing the details of the B-field spatial distribution down to radii ~100 au. Measurements of the los averaged B-field orientation using the polarized dust emission are precise to < 15° in about 75 - 95% of the independent lines of sight peering through protostellar envelopes. Large discrepancies between the integrated B-field mean orientation and the orientation reconstructed from the polarized dust emission are mostly observed in (i) lines of sight where the B-field is highly disorganized and (ii) lines of sight probing large column densities. Our analysis shows that high opacity of the thermal dust emission and low polarization fractions could be used to avoid utilizing the small fraction of measurements affected by large errors.

astro-ph.GA↗

arXiv2022

Recent progress with observations and models to characterize the magnetic fields from star-forming cores to protostellar disks

In this review paper, we aim at providing a global outlook on the progresses made in the recent years to characterize the role of magnetic fields during the embedded phases of the star formation process. Thanks to the development of observational capabilities and the parallel progress in numerical models capturing most of the important physics at work during star formation, it has recently become possible to confront detailed predictions of magnetized models to observational properties of the youngest protostars. We provide an overview of the most important consequences when adding magnetic fields to state-of-the-art models of protostellar formation, emphasizing their role to shape the resulting star(s) and their disk(s). We discuss the importance of magnetic field coupling to set the efficiency of magnetic processes, and provide a review of observational works putting constraints on the two main agents responsible for the coupling in star-forming cores: dust grains and ionized gas. We recall the physical processes and observational methods allowing to trace the magnetic field topology and its intensity in embedded protostars, and review the main steps, success and limitations in comparing real observations to synthetic observations from the non-ideal MHD models. Finally, we discuss the main threads of observational evidence that suggest a key role of magnetic fields for star and disk formation, and propose a scenario solving the angular momentum for star formation, also highlighting the remaining tensions that exist between models and observations.

astro-ph.GA↗

arXiv2021

Protoplanetary disk birth in massive star forming clumps: the essential role of the magnetic field

Protoplanetary disks form through angular momentum conservation in collapsing dense cores. In this work, we perform the first simulations with a maximal resolution down to the astronomical unit (au) of protoplanetary disk formation, through the collapse of 1000 solar mass clumps, treating self-consistently both non-ideal magnetohydrodynamics with ambipolar diffusion as well as radiative transfer in the flux-limited diffusion approximation including stellar feedback. Using the adaptive mesh-refinement code RAMSES, we investigate the influence of the magnetic field on the disks properties with three models. We show that, without magnetic fields, a population dominated by large disks is formed, which is not consistent with Class 0 disk properties as estimated from observations. The inclusion of magnetic field leads, through magnetic braking, to a very different evolution. When it is included, small < 50 au disks represent about half the population. In addition, about ~ 70% of the stars have no disk in this case which suggests that our resolution is still insufficient to preserve the smaller disks. With ambipolar diffusion, the proportion of small disks is also prominent and we report a flat mass distribution around 0.01-0.1 solar mass and a typical disk-to-star mass ratios of ~0.01-0.1. This work shows that the magnetic field and its evolution plays a prominent role in setting the initial properties of disk populations.

astro-ph.SR↗

arXiv2021

Structured velocity field in the inner envelope of B335: ALMA observations of rare CO isotopologues

Studying Class 0 objects is very important, as it allows to characterize dynamical processes at the onset of the star formation process, and to determine the physical mechanisms responsible for the outcome of the collapse. Observations of dense gas tracers allow the characterization of key kinematics of the gas directly involved in the star-formation process, such as infall, outflow or rotation. This work aims at investigating the molecular line velocity profiles of the Class 0 protostellar object B335 and attempts to put constraints on the infall motions happening in the circumstellar gas of the object.} Observations of C$^{17}$O (1-0), C$^{18}$O (1-0) and $^{12}CO$ (2-1) transitions are presented and the spectral profiles are analyzed at envelope radii between 100 and 860 au. C$^{17}$O emission presents a double peaked line profile distributed in a complex velocity field. Both peaks present an offset of 0.2 to 1 km s$^{-1}$ from the systemic velocity of the source in the probed area. The optical depth of the C$^{17}$O emission has been estimated and found to be less than 1, suggesting that the two velocity peaks trace two distinct velocity components of the gas in the inner envelope. After discarding possible motions that could produce the complex velocity pattern, such as rotation and outflow, it is concluded that infall is producing the velocity field. Because inside-out symmetric collapse cannot explain those observed profiles, it is suggested that those are produced by non-isotropic accretion from the envelope into the central source along the outflow cavity walls.

astro-ph.GA↗

arXiv2016

Cold, clumpy accretion onto an active supermassive black hole

Supermassive black holes in galaxy centres can grow by the accretion of gas, liberating energy that might regulate star formation on galaxy-wide scales. The nature of the gaseous fuel reservoirs that power black hole growth is nevertheless largely unconstrained by observations, and is instead routinely simplified as a smooth, spherical inflow of very hot gas. Recent theory and simulations instead predict that accretion can be dominated by a stochastic, clumpy distribution of very cold molecular clouds - a departure from the "hot mode" accretion model - although unambiguous observational support for this prediction remains elusive. Here we report observations that reveal a cold, clumpy accretion flow towards a supermassive black hole fuel reservoir in the nucleus of the Abell 2597 Brightest Cluster Galaxy (BCG), a nearby (redshift z=0.0821) giant elliptical galaxy surrounded by a dense halo of hot plasma. Under the right conditions, thermal instabilities can precipitate from this hot gas, producing a rain of cold clouds that fall toward the galaxy's centre, sustaining star formation amid a kiloparsec-scale molecular nebula that inhabits its core. The observations show that these cold clouds also fuel black hole accretion, revealing "shadows" cast by the molecular clouds as they move inward at about 300 kilometres per second towards the active supermassive black hole in the galaxy centre, which serves as a bright backlight. Corroborating evidence from prior observations of warmer atomic gas at extremely high spatial resolution, along with simple arguments based on geometry and probability, indicate that these clouds are within the innermost hundred parsecs of the black hole, and falling closer towards it.

astro-ph.GA↗

arXiv2014

The Earliest Stages of Star and Planet Formation: Core Collapse, and the Formation of Disks and Outflows

(Abridged) In this review we focus on the observations and theory of the formation of early disks and outflows, and their connections with the first phases of planet formation. Large rotationally supported circumstellar disks, although common around more evolved young stellar objects, are rarely detected during the earliest, "Class 0" phase; however, a few excellent candidates have been discovered recently around both low and high mass protostars. In this early phase, prominent outflows are ubiquitously observed; they are expected to be associated with at least small magnetized disks. Disk formation - once thought to be a simple consequence of the conservation of angular momentum during hydrodynamic core collapse - is far more subtle in magnetized gas. In this case, the rotation can be strongly magnetically braked. Indeed, both analytic arguments and numerical simulations have shown that disk formation is suppressed in the strict ideal magnetohydrodynamic (MHD) limit for the observed level of core magnetization. We review what is known about this "magnetic braking catastrophe", possible ways to resolve it, and the current status of early disk observations. Outflows are also intimately linked to disk formation; they are a natural product of magnetic fields and rotation and are important signposts of star formation. We review new developments on early outflow generation since PPV. The properties of early disks and outflows are a key component of planet formation in its early stages and we review these major connections.

astro-ph.SR↗