Salvatore Ferrone

Stellar streams are sensitive to perturbations from, for example, giant molecular clouds, bars and spiral arms, infalling dwarf galaxies, or globular clusters which can imprint gaps, clumps, spurs, and asymmetries in tails. In addition to these effects, the impact of a major galactic merger on a population of stellar streams remains to be explored. Here, we focus on the emergence and longevity of asymmetries between the leading and trailing tails of streams caused by such interactions. We ran collisionless N -body simulations of a Milky-Way-like galaxy hosting 36 globular cluster streams and merging with a perturber galaxy. We propose a new asymmetry metric to quantify the structural differences between both tails from their respective cumulative density profiles. We find that the over- and under-densities along streams induced by the merger depend on the orbital characteristics of their progenitors. The non-simultaneity of this effect from stream to stream implies that global asymmetry signatures are less prominent than in individual cases. These population-averaged imprints remain detectable over only 2 Gyr, but asymmetric signatures can persist over much longer periods for individual streams with wide orbits that have been perturbed prior to coalescence. We thus caution that the interpretation of streams’ morphology in the context of dark matter mapping is strongly subject to degeneracies and should be performed considering the merger history of the host.

Context. Thin stellar streams, such as those resulting from the tidal disruption of globular clusters, have long been known and used as probes of the gravitational potential of our Galaxy, both its visible and dark contents. The literature commonly interprets the presence of underdensity regions, or gaps, along these streams as being due to the close passage of dark matter subhalos. Aims. In this work, we investigate the perturbations induced on streams by the passage of dense stellar systems, such as globular clusters themselves, to test the possibility that they may cause the formation of gaps as well. In particular, we focus on the study of the stream generated by a cluster with characteristics (mass, size, and orbit) similar to those of Palomar 5, a well-known globular cluster in the Galactic halo that has particularly long tidal tails. Methods. For this purpose, we used a particle-test code to simulate the formation and evolution of the stream when subjected to the Galaxy’s gravitational field plus its whole system of globular clusters. Results. Our study shows that such a stream can be strongly perturbed by the close passage of other clusters, in particular NGC 2808, NGC 7078, and NGC 104, and that these perturbations induce the formation of gaps in the tails. Conclusions. The results of this work show that globular clusters can induce gaps in cold streams–just as it has been demonstrated in the literature for that other baryonic components, such as giant molecular clouds and the Galactic bar. Therefore, a future work that attempts to infer the dark matter subhalo distribution from stellar stream gaps must include the contributions from globular clusters.

Thin stellar streams, such as those resulting from the tidal disruption of globular clusters, have long been known and used as probes of the gravitational potential of our Galaxy, both its visible and dark contents. In particular, the presence of under-density regions, or gaps, along these streams is commonly interpreted as being due to the close passage of dark matter sub-halos. In this work, we investigate the perturbations induced on streams by the passage of dense stellar systems, such as globular clusters themselves, to test the possibility that they may cause the formation of gaps as well. In particular, we focus on the study of the stream of Palomar 5, a well-known globular cluster in the Galactic halo, which has particularly long tidal tails. For this purpose, we used a particle-test code to simulate Palomar 5's tidal tails when subjected to the Galaxy's gravitational field plus its whole system of globular clusters. Our study shows that the tails of Palomar 5 can be strongly perturbed by the close passage of other clusters, in particular of NGC 2808, NGC 7078, NGC 104, and that these perturbations induce the formation of gaps in the tails. These results show that globular clusters are capable of inducing gaps in streams--as other baryonic components such as giant molecular clouds and the galactic bar have been shown to do in other works. Therefore, when searching to construct the distribution function of dark matter sub halos within the Milky Way, the gap contribution from globular clusters must be included.

Astronomy & Astrophysics (A&A) is an international journal which publishes papers on all aspects of astronomy and astrophysics

We present an atlas and follow-up spectroscopic observations of 87 thin stream-like structures detected with the STREAMFINDER algorithm in Gaia DR3, of which 28 are new discoveries. Here, we focus on using these streams to refine mass models of the Galaxy. Fits with a double-power-law halo with the outer power-law slope set to −β _h = −3 yield an inner power-law slope of − γ h = - ( 0.97 − 0.21 + 0.17 ) , a scale radius of r 0 , h = 14.7 − 1.0 + 4.7 kpc , a halo density flattening q _m,h = 0.75 ± 0.03, and a local dark matter density of ρ _h,⊙ = 0.0114 ± 0.0007 M _⊙ pc⁻³. Freeing β yields β = 2.53 − 0.16 + 0.42 , but this value is heavily influenced by our chosen virial mass limit. The stellar disks are found to have a combined mass of 4.20 − 0.53 + 0.44 × 10 10 M ⊙ , with the thick disk contributing 12.4% ± 0.7% to the local stellar surface density. The scale lengths of the thin and thick disks are 2.17 − 0.08 + 0.18 and 1.62 − 0.13 + 0.72 kpc , respectively, while their scale heights are 0.347 − 0.010 + 0.007 and 0.86 − 0.02 + 0.03 kpc , respectively. The virial mass of the favored model is M 200 = 1.09 − 0.14 + 0.19 × 10 12 M ⊙ , while the mass inside of 50 kpc is M _{R = 0.46 ± 0.03 × 10¹² M ⊙. We introduce the Large Magellanic Cloud (LMC) into the derived potential models, and fit the Orphan stream therein, finding a mass for the LMC that is consistent with recent estimates. Some salient highlights include the nearby trailing arm of ω Cen, and a nearby very metal-poor stream that was once a satellite of the Sagittarius dwarf galaxy. Finally, we unambiguously detect a hot component around the GD-1 stream, consistent with it having been tidally preprocessed within its own dark matter subhalo.}

OSIRIS-REx is a sample return mission to near-Earth Asteroid (101955) Bennu (Lauretta et al. 2017). The asteroid is spectrally classified as a B-type (Clark et al. 2011), and phyllosilicates similar to those found in carbonaceous chondrites have been detected on its surface (Hamilton et al. 2019). Bennu has a relatively flat (and blue) reflectance spectrum in the 0.4 to 3.7 micron spectral range and has a low albedo of ~4.5% (Golish et al. 2020).Bennu has a rough and rocky surface. Imaging data from the OSIRIS-REx Camera Suite (OCAMS; Rizk et al. 2018) reveals that boulders in the size range from 1 to 10 meters dominate the surface (Lauretta et al. 2019; DellaGiustina and Emery et al. 2019). Observed boulder textures range from smooth to hummocky and breccia-like (Walsh et al. 2019; DellaGiustina and Emery et al. 2019). The smoother rocks appear to be smaller, brighter, and more angular, while the rougher rocks appear to be larger, darker, and highly textured. Because spectral variations on Bennu are subtle and associated with albedo (Clark et al. 2019), the question arises: Could the observed color variations be due to texture variations alone, or are space-weathering variations required to explain the observations? To isolate the spectral effects of texture on the spectral properties of Bennu, we first simulate Bennu’s spectrum using a two-component mixture, then we check to see whether texture changes in this analog can account for the observed color and albedo trends. Simulated Bennu Spectral Analog: We synthesized physical mixtures of saponite (SAP105 with ~25 wt.% dolomite) with two forms of carbon:

Context. Recently, a primordial family of moderate-albedo asteroid fragments was discovered in the inner main belt. Its age was estimated to be 4.4 ± 1.7 Gyr. However, there is a lack of compositional characterization, which is important to the study of the earliest collisions in the main belt. Aims. In addition to the previously identified members and the parameters that define the family’s borders (V shape), we expanded the list of family members to include asteroids located within the central region of the V shape. These additional potential members were selected based on their diameter (larger than 7 km) and their geometric visible albedo (greater than or equal to 12%). Subsequently, we conducted a spectroscopic survey to determine the dominant taxonomy and composition of this family. This allowed us to further refine the list of family members by removing interlopers. Methods. From an initial list of 263 asteroids that are considered to be potential members of the aforementioned primordial family, we retrieved their spectra in the visible and near-infrared range from the literature and from the Gala DR3 spectral catalog of Solar System objects. For asteroids with no or poor signal-to-noise ratio spectra in the literature, we carried out new ground-based observations. We obtained new spectra for 33 members of the family using the 1.82 m Asiago Telescope for the visible spectroscopy, while for near-infrared spectroscopy, we used the 3.58 m Telescopio Nazionale Galileo (TNG) and the 4.30 m Lowell Discovery Telescope (LDT). Results. In total, we collected spectra for 261 potential members of the primordial S-type family out of 263. We determined their spectral taxonomy and properties, such as spectral slopes and absorption band parameters, when existing. Using the taxonomical characterization and the orbital space parameters, we identified and removed 71 interlopers from the potential members list. The final list of the primordial S-type family members includes 190 asteroids. The family is dominated by S-complex (~71%) asteroids with a mineralogy similar to ordinary chondrites and pyroxene-rich minerals. The family also contains members classified as L-types and V-types. (~15% and ~9%, respectively). Conclusions. The mean albedo of the family is ~23%, and its largest probable remnant is the asteroid (30) Urania. The estimated size of the family parent body ranges between 110 and 210 km. This size range is compatible with the progenitor of H and L chondrites.

Context. Understanding the conditions that lead to the formation of planetesimals – the building blocks of planets - and their initial size distribution is a central problem of modern planetology. While most of these original planetesimals were accreted onto the terrestrial planets and the cores of the giant planets, some were also stranded in the main belt, where 4.5 Gyr of collisional evolution broke most of them into families of collisional asteroid fragments. However, some planetesimals survived, and are still hidden amongst asteroid fragments in the main belt. Aims. We make use of astronomical data to identify these leftover planetesimals amongst all other asteroids. Our search is based on separating planetesimal survivors from families of asteroids generated by collisions. Namely, we aim to identify and “clean” the main belt of collisional family members: by doing so, we would be left with the surviving members of the original planetesimals. Methods. We focus here on the inner portion of the main belt for asteroids with intermediate to high albedo. It is known that current asteroid family catalogs are not suitable for the aforementioned cleaning; they are conservative and only one-quarter of the known asteroids are associated with the approximately 120 distinct asteroid families. We therefore developed methods to inclusively link asteroids to known collisional families in order to better capture their extent. Namely, we apply a hierarchical clustering method (HCM) on asteroids filtered according to the V-shape of the Yarkovsky drift of each family in order to reassess family membership (V-shape-constrained HCM). The identified families were removed and the remaining background population was searched for previously undetected collisional families. Results. We succeed in using our V-shape-constrained HCM to link family “halos” to their cores. After removing these reassessed families from the asteroid population, our V-shape search reveals a previously unknown collisional family of S-type asteroids in the inner main belt with an age of 4.3 ± 1.7 Gyr and a significance level of 3.4σ. When this ancient collisional family is removed, 34 planetesimals are identified and their size-frequency distribution is presented. Conclusions. The asteroid belt has two components: planetesimals and collisional fragments. The cumulative size-frequency distribution of planetesimals has a steep power-law index for bodies larger than 100 km in diameter and a much smaller power-law index for planetesimals smaller than 100 km.

We present the e-TidalGCs project, aimed at modeling and predicting the extra-tidal features surrounding all Galactic globular clusters for which 6D phase-space information, masses, and sizes are available (currently numbering 159 globular clusters). We focus the analysis and presentation of the results on the distribution of extra-tidal material on the sky, as well as on the different structures found at different heliocentric distances. We emphasize the wide variety of morphologies found: beyond the canonical tidal tails, our models reveal that the extra-tidal features generated by globular clusters take a wide variety of shapes, from thin and elongated shapes to thick and complex halo-like structures. We also compare some of the most well-studied stellar streams found around Galactic globular clusters to our model predictions, namely, those associated with the clusters NGC 3201, NGC 4590, NGC 5466, and Pal 5. Additionally, we investigate how the distribution and extension in the sky of the simulated streams vary with the Galactic potential by making use of three different models, either containing a central spheroid, not containing one, or containing a stellar bar. Overall, our models predict that the mass lost by the current globular cluster population in the field from the last 5 Gyrs is between 0.3 − 2.1 × 10⁷ M_⊙. This amount is comparable to a value between 7–55% of the current mass. Most of this lost mass is found in the inner Galaxy, with the half-mass radius of this population being between 4–6 kpc. The outputs of the simulations will be publicly available, coinciding with the unique opportunity presented by the delivery of the ESA Gaia mission and complementary spectroscopic surveys. Their exquisite data will offer the possibility to carry out novel comparisons with the models discussed in this work.