OSSOS. V. Diffusion in the Orbit of a High-perihelion Distant Solar System Object

We report the discovery of the minor planet 2013 SY$_{99}$, on an exceptionally distant, highly eccentric orbit. With a perihelion of 50.0 au, 2013 SY$_{99}$'s orbit has a semi-major axis of $730 \pm 40$ au, the largest known for a high-perihelion trans-Neptunian object (TNO), well beyond those of (90377) Sedna and 2012 VP$_{113}$. Yet, with an aphelion of $1420 \pm 90$ au, 2013 SY$_{99}$'s orbit is interior to the region influenced by Galactic tides. Such TNOs are not thought to be produced in the current known planetary architecture of the Solar System, and they have informed the recent debate on the existence of a distant giant planet. Photometry from the Canada-France-Hawaii Telescope, Gemini North and Subaru indicate 2013 SY$_{99}$ is $\sim 250$ km in diameter and moderately red in colour, similar to other dynamically excited TNOs. Our dynamical simulations show that Neptune's weak influence during 2013 SY$_{99}$'s perihelia encounters drives diffusion in its semi-major axis of hundreds of astronomical units over 4 Gyr. The overall symmetry of random walks in semi-major axis allow diffusion to populate 2013 SY$_{99}$'s orbital parameter space from the 1000-2000 au inner fringe of the Oort cloud. Diffusion affects other known TNOs on orbits with perihelia of 45 to 49 au and semi-major axes beyond 250 au, providing a formation mechanism that implies an extended population, gently cycling into and returning from the inner fringe of the Oort cloud.Comment: First reviewer report comments incorporated. Comments welcom

Fitting the integrated Spectral Energy Distributions of Galaxies

Fitting the spectral energy distributions (SEDs) of galaxies is an almost universally used technique that has matured significantly in the last decade. Model predictions and fitting procedures have improved significantly over this time, attempting to keep up with the vastly increased volume and quality of available data. We review here the field of SED fitting, describing the modelling of ultraviolet to infrared galaxy SEDs, the creation of multiwavelength data sets, and the methods used to fit model SEDs to observed galaxy data sets. We touch upon the achievements and challenges in the major ingredients of SED fitting, with a special emphasis on describing the interplay between the quality of the available data, the quality of the available models, and the best fitting technique to use in order to obtain a realistic measurement as well as realistic uncertainties. We conclude that SED fitting can be used effectively to derive a range of physical properties of galaxies, such as redshift, stellar masses, star formation rates, dust masses, and metallicities, with care taken not to over-interpret the available data. Yet there still exist many issues such as estimating the age of the oldest stars in a galaxy, finer details ofdust properties and dust-star geometry, and the influences of poorly understood, luminous stellar types and phases. The challenge for the coming years will be to improve both the models and the observational data sets to resolve these uncertainties. The present review will be made available on an interactive, moderated web page (sedfitting.org), where the community can access and change the text. The intention is to expand the text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics & Space Scienc

The geology and geophysics of Kuiper Belt object (486958) Arrokoth

The Cold Classical Kuiper Belt, a class of small bodies in undisturbed orbits beyond Neptune, are primitive objects preserving information about Solar System formation. The New Horizons spacecraft flew past one of these objects, the 36 km long contact binary (486958) Arrokoth (2014 MU69), in January 2019. Images from the flyby show that Arrokoth has no detectable rings, and no satellites (larger than 180 meters diameter) within a radius of 8000 km, and has a lightly-cratered smooth surface with complex geological features, unlike those on previously visited Solar System bodies. The density of impact craters indicates the surface dates from the formation of the Solar System. The two lobes of the contact binary have closely aligned poles and equators, constraining their accretion mechanism

OSSOS. XXVI. On the Lack of Catastrophic Collisions in the Present Kuiper Belt

We investigate different conditions, including the orbital and size-frequency distribution (SFD) of the early Kuiper Belt, that can trigger catastrophic planetesimal destruction. The goal of this study is to test if there is evidence for collisional grinding in the Kuiper Belt that has occurred since its formation. This analysis has important implications for whether the present-day SFD of the cold classical trans-Neptunian objects (TNOs) is a result of collisional equilibrium or if it reflects the primordial stage of planetesimal accretion. As an input to our modeling, we use the most up-to-date debiased OSSOS++ ensemble sample of the TNO population and orbital model based on the present-day architecture of the Kuiper Belt. We calculate the specific impact energies between impactor-target pairs from different TNO groups and compare our computed energies to catastrophic disruption results from smoothed particle hydrodynamics simulations. We explore different scenarios by considering different total primordial Kuiper Belt masses and power slopes of the SFD and allowing collisions to take place over different timescales. The collisional evolution of the Kuiper Belt is a strong function of the unknown initial mass in the trans-Neptunian region, where collisional grinding of planetesimals requires a total primordial Kuiper Belt mass of M > 5 M ⊕, collision speeds as high as 3 km s−1, and collisions over at least 0.5 Gyr. We conclude that presently, most of the collisions in the trans-Neptunian region are in the cratering rather than disruption regime. Given the low collision rates among the cold classical Kuiper Belt objects, their SFD most likely represents the primordial planetesimal accretion. © 2022. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

OSSOS. XVII. An upper limit on the number of distant planetary objects in the Solar System

International audienceBeyond the giant planets there is a collection of bodies left over from the epoch of planet formation. The objects that are just beyond Neptune are more easily detected than those that journey hundreds of au away; all such highly eccentric objects have been observed inside 150 au. We are interested here in a population of Pluto to Mars-sized planets that were almost certainly present in the early Solar System, some of which may now be stranded in the distant Solar System. Using data from the Outer Solar System Origins Survey (OSSOS), which covers ~167 square degrees down to r ~25, we searched for objects beyond 300 au using a rarely used search technique. To find such objects we created catalogues of all the sources that were stationary (to the level of the astronomical seeing) in three images taken over 2 h. We then searched for which such 'stationary' objects were not present days/weeks/months before and after. Although other astronomical phenomena (e.g. supernovae) were discovered, no slow moving Solar System object was found. From the null detection and using a survey simulator, we obtain a model-dependent 95% upper limit of ~1000 on the number of 'planetary' objects (with absolute magnitudes, H r , <2) in the distant Solar System. To our knowledge this is the first published limit for objects of this scale beyond 300 au. We show that if there are a small number of Mars-scale objects still in the distant Solar System, despite being brighter they may have escaped detection in other surveys due to their slow rates of motion

OSSOS. XIX. Testing Early Solar System Dynamical Models Using OSSOS Centaur Detections

International audienc

Col-ossos: The distinct color distribution of single and binary cold classical kbos

The cold classical Kuiper Belt Objects (KBOs) possess a high,gsim;30% binary fraction. Widely separated and dynamically fragile, these binary systems have been useful in tracing the origins of KBOs. A new class of binaries was recently identified by their colors. The so-called blue binaries are unanimously members of the less red compositional class, and exhibit a 100% binary fraction. They appear to be push-out survivors, emplaced in the classical region during Neptune's phases of outward migration. The presence of these binary systems implies that the majority of objects that formed near the cold classical region formed as binaries. Here we present new optical color measurements of cold classical KBOs from the Colors of the Outer Solar System Origins Survey, including colors of a blue binary discovered by the Solar System Origins Legacy Survey-2015 RJ277. The increased size of the colors sample has resulted in order-of-magnitude decrease in the probability that the binaries and singles sample share the same color distribution. From the Anderson-Darling statistic, this probability is only a 0.3%, while it is only 0.002% when utilizing the difference of means statistic. We find a hint that the blue binaries have inflated free inclinations compared to their red counterparts, consistent with the push-out origin for these bodies. © 2021 The Author(s).Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Observing the stellar halo of Andromeda in cosmological simulations: the Auriga2PAndAS pipeline

International audienceWe present a direct comparison of the Pan-Andromeda Archaeological Survey (PAndAS) observations of the stellar halo of M31 with the stellar halos of six galaxies from the Auriga simulations. We process the simulated halos through the Auriga2PAndAS pipeline and create PAndAS-like mocks that fold in all observational limitations of the survey data (foreground contamination from the Milky Way stars, incompleteness of the stellar catalogs, photometric uncertainties, etc.). This allows us to study the survey data and the mocks in the same way and generate directly comparable density maps and radial density profiles. We show that the simulations are overall compatible with the observations. Nevertheless, some systematic differences exist, such as a preponderance for metal-rich stars in the mocks. While these differences could suggest that M31 had a different accretion history or has a different mass compared with the simulated systems, it is more likely a consequence of an underquenching of the star formation history of galaxies, related to the resolution of the Auriga simulations. The direct comparison enabled by our approach offers avenues to improve our understanding of galaxy formation as they can help pinpoint the observable differences between observations and simulations. Ideally, this approach will be further developed through an application to other stellar halo simulations. To facilitate this step, we release the pipeline to generate the mocks, along with the six mocks presented and used in this contribution

OSSOS: The eccentricity and inclination distributions of the stable neptunian Trojans

International audienceThe minor planets on orbits that are dynamically stable in Neptune's 1:1 resonance on Gyr timescales were likely em:laced by Neptune's outward migration. We explore the intrinsic libration amplitude, eccentricity, and inclination distribution of Neptune's stable Trojans, using the detections and survey efficiency of the Outer Solar System Origins Survey (OSSOS) and Pan-STARRS1. We find that the libration amplitude of the stable Neptunian Trojan population can be well modeled as a Rayleigh distribution with a libration amplitude width σ A φ of 15 •. When taken as a whole, the Neptune Trojan population can be acceptably modeled with a Rayleigh eccentricity distribution of width σ e of 0.045 and a typical sin(i) × Gaussian inclination distribution with a width σ i of 14 ± 2 • ; however, these distributions are only marginally acceptable. This is likely because, even after accounting for survey detection biases, the known large (H r < 8) and small (H r ≥ 8) Neptune Trojans appear to have markedly different eccentricities and inclinations. We propose that like the classical Kuiper belt, the stable intrinsic Neptunian Trojan population have dynamically 'hot' and dynamically 'cold' components to its eccentricity/inclination distribution, with σ e−cold ∼ 0.02/σ i−cold ∼ 6 • and σ e−hot ∼ 0.05/σ i−hot ∼ 18 •. In this scenario, the 'cold' L4 Neptunian Trojan population lacks the H r ≥ 8.0 members and has 13 +11 −6 'cold' Trojans with H r < 8.0. On the other hand, the 'hot' L4 Neptunian Trojan population has 136 +84 −75 Trojans with H r < 10-a population 2.4 times greater than that of the L4 Jovian Trojans in the same luminosity range