arXiv subjects

Jean-Marc Hure

Publications and source records attributed to Jean-Marc Hure.

9 recordsLinked to original sources

arXiv2016

Mapping CO Gas in the GG Tauri A Triple System with 50 AU Spatial Resolution

We aim to unveil the observational imprint of physical mechanisms that govern planetary formation in the young, multiple system GG Tau A. We present ALMA observations of $^{12}$CO and $^{13}$CO 3-2 and 0.9 mm continuum emission with 0.35" resolution. The $^{12}$CO 3-2 emission, found within the cavity of the circumternary dust ring (at radius $< 180$ AU) where no $^{13}$CO emission is detected, confirms the presence of CO gas near the circumstellar disk of GG Tau Aa. The outer disk and the recently detected hot spot lying at the outer edge of the dust ring are mapped both in $^{12}$CO and $^{13}$CO. The gas emission in the outer disk can be radially decomposed as a series of slightly overlapping Gaussian rings, suggesting the presence of unresolved gaps or dips. The dip closest to the disk center lies at a radius very close to the hot spot location at $\sim250-260$~AU. The CO excitation conditions indicate that the outer disk remains in the shadow of the ring. The hot spot probably results from local heating processes. The two latter points reinforce the hypothesis that the hot spot is created by an embedded proto-planet shepherding the outer disk.

astro-ph.GA↗

arXiv2016

Asymmetric mass models of disk galaxies - I. Messier 99

Mass models of galactic disks traditionally rely on axisymmetric density and rotation curves, paradoxically acting as if their most remarkable asymmetric features, such as lopsidedness or spiral arms, were not important. In this article, we relax the axisymmetry approximation and introduce a methodology that derives 3D gravitational potentials of disk-like objects and robustly estimates the impacts of asymmetries on circular velocities in the disk midplane. Mass distribution models can then be directly fitted to asymmetric line-of-sight velocity fields. Applied to the grand-design spiral M99, the new strategy shows that circular velocities are highly nonuniform, particularly in the inner disk of the galaxy, as a natural response to the perturbed gravitational potential of luminous matter. A cuspy inner density profile of dark matter is found in M99, in the usual case where luminous and dark matter share the same center. The impact of the velocity nonuniformity is to make the inner profile less steep, although the density remains cuspy. On another hand, a model where the halo is core dominated and shifted by 2.2-2.5 kpc from the luminous mass center is more appropriate to explain most of the kinematical lopsidedness evidenced in the velocity field of M99. However, the gravitational potential of luminous baryons is not asymmetric enough to explain the kinematical lopsidedness of the innermost regions, irrespective of the density shape of dark matter. This discrepancy points out the necessity of an additional dynamical process in these regions: possibly a lopsided distribution of dark matter.

astro-ph.GA↗

arXiv2005

How does disk gravity really influence type-I migration ?

We report an analytical expression for the locations of Lindblad resonances induced by a perturbing protoplanet, including the effect of disk gravity. Inner, outer and differential torques are found to be enhanced compared to situations where a keplerian velocity field for the dynamics of both the disk and the planet is assumed. Inward migration is strongly accelerated when the disk gravity is only accounted for in the planet orbital motion. The addition of disk self-gravity slows down the planet drift but not enough to stop it.

astro-ph↗

arXiv2005

Accurate numerical potential and field in razor-thin axisymmetric discs

We demonstrate the high accuracy of the density splitting method to compute the gravitational potential and field in the plane of razor-thin, axially symmetric discs, as preliminarily outlined in Pierens & Hure (2004). Because residual kernels in Poisson integrals are not C^infinity-class functions, we use a dynamical space mapping in order to increase the efficiency of advanced quadrature schemes. In terms of accuracy, results are better by orders of magnitude than for the classical FFT-methods.

astro-ph↗

arXiv2002

Self-gravitating discs: what can we learn from the dynamics of maser spots ?

For a few nearby active nuclei, the disc orbiting the black hole is traced by water maser emission. By combining a simple model together with observed velocity profiles, we show that it is possible to put constraints on the black hole mass and on the distribution of matter (shape, density, size) in the outer disc. We then report possible parameters for the non-keplerian disc and for the black hole in NGC 1068, and mention an uncertainty of at least 25% on the central mass in NGC 4258.

astro-ph↗

arXiv2002

Origin of non-keplerian motions of masers in NGC 1068

We demonstrate that the ``sub-keplerian'' rotation curve of maser spots in NGC 1068 can be explained by the gravitational attraction of the disc orbiting the central black hole. Possible parameters matching observations are: black hole mass of 12 million solar masses, disc outer edge > 1.3 pc, aspect ratio in the range 0.003 to 0.3, surface density varying approximately as 1/R, and disc mass of about 9.4 million solar masses. The physical conditions required for the excitation of masers are fulfilled, and the outer disc would stand in a gravitationally marginally stable state.

astro-ph↗

arXiv2001

Size-Mass-luminosity relations in AGN and the role of the accretion disc

We address the question of the relations between the black hole's mass, the accretion rate, the bolometric luminosity, the optical luminosity and the size of the Broad Line Region (BLR) in Active Galactic Nuclei, using recent observational data obtained from monitoring campaigns. We show that a standard accretion disc cannot account for the observed optical luminosity, unless it radiates at super-Eddington rates. This implies the existence of another, dominant emission mechanism in the optical range, or a non standard disc (non stationary, ADAF and/or strong outflows). Narrow Line Seyfert 1 galaxies (NLS1s) are most extreme in this context: they have larger bolometric to Eddington luminosity ratios than Broad Line Seyfert 1 (BLS1s), and most likely a larger "non disc" component in the optical range. From realistic simulations of self-gravitating $α$-discs, we have systematically localized the gravitationally unstable disc and shown that, given uncertainties on both the model and observations, it coincides quite well with the size of the BLR. We therefore suggest that the gravitationally unstable disc is the source which releases BLR clouds in the medium. However the influence of the ionization parameter is also required to explain the correlation found between the size of the BLR and the luminosity. In this picture the size of the BLR in NLS1s (relative to the black hole size) is larger (and the emission line width smaller) than in BLS1s simply because their Eddington ratio is larger.

astro-ph↗

arXiv2000

On the transition to self-gravity in low mass AGN and YSO accretion discs

The equations governing the vertical structure of a stationary keplerian accretion disc are presented. The model is based on the alpha-viscosity, includes self-gravity, convective transport and turbulent pressure. A few properties of the model are discussed for circumstellar and AGN discs. We show the strong sensitivity of the disc structure to the viscous energy deposition towards the vertical axis, specially when entering inside the self-gravitating part of the disc. The local version of the alpha-prescription leads to a "singular" behavior which is also predicted by the vertically averaged model. With respect, a much softer transition is observed with the "alpha-P" formalism. Turbulent pressure is important only for alpha > 0.1. It lowers vertical density gradients, significantly thickens the disc, tends to wash out density inversions and pushes the self-gravitating region to slightly larger radii. Curves localizing the inner edge of the self-gravitating disc as functions of the viscosity parameter and accretion rate are given. The lower alpha, the closer to the center the self-gravitating regime, and the sensitivity to the accretion rate is generally weak, except for alpha < 0.1. This study suggests that models aiming to describe T-Tauri discs beyond about a few to a few tens astronomical units from the central protostar using the alpha-theory should consider vertical self-gravity. The Primitive Solar Nebula was probably a bit (if not strongly) self-gravitating at the actual orbit of giant planets. Alpha-discs hosted by active galaxies are self-gravitating beyond about a thousand Schwarzchild radii. The inferred surface density remains too high to lower the accretion time scale. More efficient mechanisms driving accretion are required.

astro-ph↗

arXiv1998

Accretion disc outbursts: a new version of an old model

We have developed 1D time-dependent numerical models of accretion discs, using an adaptive grid technique and an implicit numerical scheme, in which the disc size is allowed to vary with time. The code fully resolves the cooling and heating fronts propagating in the disc. We show that models in which the radius of the outer edge of the disc is fixed produce incorrect results, from which probably incorrect conclusions about the viscosity law have been inferred. In particular we show that outside-in outbursts are possible when a standard bimodal behaviour of the Shakura-Sunyaev viscosity parameter alpha is used. We also discuss to what extent insufficient grid resolutions have limited the predictive power of previous models. We find that the global properties (magnitudes, etc. ...) of transient discs can be addressed by codes using a high, but reasonable, number of fixed grid points. However, the study of the detailed physical properties of the transition fronts generally requires resolutions which are out of reach of fixed grid codes. It appears that most time-dependent models of accretion discs published in the literature have been limited by resolution effects, improper outer boundary conditions, or both.

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