ALMA Reveals an Eccentricity Gradient in the Fomalhaut Debris Disk

Abstract

We present evidence of a negative eccentricity gradient in the debris disk of the nearby A-type main sequence star, Fomalhaut. Fitting to the high-resolution, archival ALMA 1.32 mm continuum data for Fomalhaut (with a synthesised angular resolution of $0.76\times 0.55^{\prime \prime }$; 4-6\,au), we present a model that describes the bulk properties of the disk (semi-major axis, width, and geometry) and its asymmetric morphology. The best-fit model incorporates a forced eccentricity gradient that varies with semi-major axis, $e_f\propto a^{n_{\mathrm{pow}}}$, a generalized form of the parametric models of Lynch & Lovell 2022, with $n_{\mathrm{pow}}=-1.75\pm 0.16$. We show that this model is statistically preferred to models with constant forced and free eccentricities. In comparison to disk models with constant forced eccentricities, negative eccentricity gradient models broaden disk widths at pericenter versus apocenter, and increase disk surface densities at apocenter versus pericenter, both of which are seen in the Fomalhaut disk, and which we collectively term Eccentric Velocity Divergence. We propose single-planet architectures consistent with the model and investigate the stability of the disk over 440 Myr to planet-disk interactions via N-body modeling. We find that Fomalhaut's ring eccentricity plausibly formed during the protoplanetary disk stage, with subsequent planet-disk interactions responsible for carving the disk morphology.

Accepted for publication in ApJ; 22 pages, 10 figures, 3 tables

References in corpus (23)

• Optical Images of an Exosolar Planet 25 Light Years from Earth
• Detection of exocometary CO within the 440 Myr-old Fomalhaut belt: a similar CO+CO${}_2$ ice abundance in exocomets and Solar System comets
• Herschel images of Fomalhaut. An extrasolar Kuiper Belt at the height of its dynamical activity
• A Complete ALMA Map of the Fomalhaut Debris Disk
• CO mass upper limits in the Fomalhaut ring - the importance of NLTE excitation in debris discs and future prospects with ALMA
• Planetary chaotic zone clearing: destinations and timescales
• Solution to the debris disc mass problem: planetesimals are born small?
• Discovery of an Extremely Short Duration Flare from Proxima Centauri Using Millimeter through FUV Observations
• Apocenter glow in eccentric debris disks: implications for Fomalhaut and epsilon Eridani
• Spatially resolved imaging of the inner Fomalhaut disk using JWST/MIRI
• New HST data and modeling reveal a massive planetesimal collision around Fomalhaut
• High resolution ALMA and HST images of q${}^1$ Eri: an asymmetric debris disc with an eccentric Jupiter
• The unexpected narrowness of eccentric debris rings: a sign of eccentricity during the protoplanetary disc phase
• ALMA 870 $\mu$m continuum observations of HD 100546. Evidence of a giant planet on a wide orbit
• Circumbinary and circumstellar discs around the eccentric binary IRAS 04158+2805 -- a testbed for binary-disc interaction
• Fomalhaut b could be massive and sculpting the narrow, eccentric debris disc, if in mean-motion resonance with it
• Eccentric Dust Ring in the IRS 48 Transition Disk
• Eccentric debris disc morphologies I: exploring the origin of apocentre and pericentre glows in face-on debris discs
• Submillimeter Observations of the Young Low-Mass Object IRAS 04158+2805
• Debris Disks in Multi-Planet Systems: Are Our Inferences Compromised by Unseen Planets?
• Resolving the outer ring of HD 38206 using ALMA and constraining limits on planets in the system
• High resolution ALMA and HST imaging of $\kappa$CrB: a broad debris disc around a post-main sequence star with low-mass companions
• High Resolution ALMA Data of the Fomalhaut Debris Disk Confirms Apsidal Width Variation

Cited by in corpus (2)

• The ALMA survey to Resolve exoKuiper belt Substructures (ARKS): VI. Asymmetries and offsets
• High Resolution ALMA Data of the Fomalhaut Debris Disk Confirms Apsidal Width Variation