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We use the photometric metallicities provided by the panoramic Pristine survey to study the veracity and derive the metallicities of the numerous stellar streams found by the application of the STREAMFINDER algorithm to the Gaia Early Data Release 3 data. All 26 streams present in Pristine show a clear metallicity distribution function, which provides an independent check of the reality of these structures, supporting the reliability of STREAMFINDER in finding streams and the power of Pristine to measure precise metallicities. We further present six candidate structures with coherent phase-space and metallicity signals that are very likely streams. The majority of studied streams are very metal-poor (14 structures with [Fe/H] < −2.0) and include three systems with [Fe/H] < −2.9 (C-11, C-19, and C-20). These streams could be the closest debris of low-luminosity dwarf galaxies or may have originated from globular clusters of significantly lower metallicity than any known current Milky Way globular cluster. Our study shows that the promise of the Gaia data for Galactic Archeology studies can be substantially strengthened by quality photometric metallicities, allowing us to peer back into the earliest epochs of the formation of our Galaxy and its stellar halo constituents. [ABSTRACT FROM AUTHOR]

The C-19 stream is the most metal-poor stellar system ever discovered, with a mean metallicity [Fe/H] = −3.38 ± 0.06. Its low metallicity dispersion (σ[Fe/H] < 0.18 at the 95 per cent confidence level) and variations in sodium abundances strongly suggest a globular cluster origin. In this work, we use Very Large Telescope (VLT)/UV–Visual Echelle Spectrograph (UVES) spectra of seven C-19 stars to derive more precise velocity measurements for member stars, and to identify two new members with radial velocities and metallicities consistent with the stream's properties. One of these new member stars is located 30° away from the previously identified body of C-19, implying that the stream is significantly more extended than previously known and that more members likely await discovery. In the main part of C-19, we measure a radial velocity dispersion σ v = 6.2 |$^{+2.0}_{-1.4}{\rm \, km\, s^{-1}}$| from nine members, and a stream width of 0.56° ± 0.08°, equivalent to ∼158 pc at a heliocentric distance of 18 kpc. These confirm that C-19 is comparatively hotter, dynamically, than other known globular cluster streams and shares the properties of faint dwarf galaxy streams. On the other hand, the variations in the Na abundances of the three newly observed bright member stars, the variations in Mg and Al for two of them, and the normal Ba abundance of the one star where it can be measured provide further evidence for a globular cluster origin. The tension between the dynamical and chemical properties of C-19 suggests that its progenitor experienced a complex birth environment or disruption history. [ABSTRACT FROM AUTHOR]

We present a suite of three-dimensional, high-resolution hydrodynamic simulations that follow the evolution of a massive (107 M⊙) pressure-confined, star-forming neutral gas cloud moving through a hot intracluster medium (ICM). The main goal of the analysis is to get theoretical insight into the lifetimes and evolution of stellar systems like the recently discovered star-forming cloud SECCO 1 in the Virgo cluster of galaxies, but it may be of general interest for the study of the star-forming gas clumps that are observed in the tails of ram pressure stripped galaxies. Building up on a previous, simple simulation, we explored the effect of different relative velocity of the cloud and larger temperature of the ICM, as well as the effect of the cloud self-gravity. Moreover, we performed a simulation including star formation and stellar feedback, allowing for a first time a direct comparison with the observed properties of the stars in the system. The survivability of the cold gas in the simulated clouds is granted on time-scales of the order of 1 Gyr, with final cold gas fractions generally >0.75. In all cases, the simulated systems end up, after 1 Gyr of evolution, as symmetric clouds in pressure equilibrium with the external hot gas. We also confirm that gravity played a negligible role at the largest scales on the evolution of the clouds. In our simulation with star formation, star formation begins immediately, it peaks at the earliest times, and decreases monotonically with time. Inhomogeneous supernova explosions are the cause of an asymmetric shape of the gas cloud, facilitating the development of instabilities and the decrease of the cold gas fraction. [ABSTRACT FROM AUTHOR]

We present radial velocities for five member stars of the recently discovered young (age ≃ 100−150 Myr) stellar system Price-Whelan 1 (PW 1), which is located far away in the Galactic Halo (D≃ 29 kpc, Z≃ 15 kpc), and that is probably associated with the leading arm (LA) of the Magellanic Stream. We measure the systemic radial velocity of PW 1, V r = 275 ± 10 km s−1, significantly larger than the velocity of the LA gas in the same direction. We re-discuss the main properties and the origin of this system in the light of these new observations, computing the orbit of the system and comparing its velocity with that of the H  i in its surroundings. We show that the bulk of the gas at the velocity of the stars is more than 10 deg (5 kpc) away from PW 1 and the velocity difference between the gas and the stars becomes larger as gas closer to the stars is considered. We discuss the possibilities that (1) the parent gas cloud was dissolved by the interaction with the Galactic gas, and (2) that the parent cloud is the high-velocity cloud (HVC) 287.5+22.5 + 240, lagging behind the stellar system by ≃ 25 km s−1 and ≃10 deg ≃ 5 kpc. This HVC, which is part of the LA, has metallicity similar to PW 1, displays a strong magnetic field that should help to stabilize the cloud against ram pressure, and shows traces of molecular hydrogen. We also show that the system is constituted of three distinct pieces that do not differ only by position in the sky but also by stellar content. [ABSTRACT FROM AUTHOR]

The Large Magellanic Cloud (LMC) hosts a large number of candidate stellar cluster pairs. Binary stellar clusters provide important clues about cluster formation processes and the evolutionary history of the host galaxy. However, to properly extract and interpret this information, it is crucial to fully constrain the fraction of real binary systems and their physical properties. Here we present a detailed photometric analysis based on ESO-FORS2 images of three candidate cluster multiplets in the LMC, namely SL349-SL353, SL385-SL387--NGC 1922 and NGC 1836--BRHT4b--NGC 1839. For each cluster, we derived ages, structural parameters and morphological properties.We have also estimated the degree of filling of their Roche lobe, as an approximate tool to measure the strength of the tidal perturbations induced by the LMC. We find that themembers of the possible pairs SL349--SL353 and BRHT4b--NGC 1839 have a similar age (t = 1.00 ± 0.12 Gyr and t = 140 ± 15 Myr, respectively), thus possibly hinting at a common origin of their member systems. We also find that all candidate pairs in our sample show evidence of intracluster overdensities that can be a possible indication of real binarity. Particularly interesting is the case of SL349--SL353. In fact, SL353 is relatively close to the condition of critical filling, thus suggesting that these systems might actually constitute an energetically bound pair. It is therefore key to pursue a detailed kinematic screening of such clusters, without which, at present, we do not dare making a conclusive statement about the true nature of this putative pair. [ABSTRACT FROM AUTHOR]

We present different chemical evolution models for the ultrafaint dwarf galaxy Boötes I. We either assume that the galaxy accretes its mass through smooth infall of gas of primordial chemical composition (classical models) or adopt mass accretion histories derived from the combination of merger trees with semi-analytical modelling (cosmologically-motivated models). Furthermore, we consider models with and without taking into account inhomogeneous mixing in the interstellar medium within the galaxy, i.e. homogeneous versus inhomogeneous models. The theoretical predictions are then compared to each other and to the body of the available data. From this analysis, we confirm previous findings that Boötes I has formed stars with very low efficiency but, at variance with previous studies, we do not find a clear-cut indication that supernova explosions have sustained long-lasting galactic-scale outflows in this galaxy. Therefore, we suggest that external mechanisms such as ram pressure stripping and tidal stripping are needed to explain the absence of neutral gas in Boötes I today. [ABSTRACT FROM AUTHOR]

This paper concludes a systematic search for evidence of the Monoceros Ring and Canis Major dwarf galaxy around the Galactic plane. Presented here are the results for the Galactic longitude range of l= (280–025)°. Testing the claim that the Monoceros Ring encircles the entire Galaxy, this survey attempts to document the position of the Monoceros Ring with increasing Galactic longitude. Additionally, with the discovery of the purported Canis Major dwarf galaxy, searching for more evidence of its interaction is imperative for tracing its path through the Galaxy and understanding its role in the evolution of the Milky Way. Two new detections of the Monoceros Ring have been found at and (300, +10)°. Interestingly, in general, there seem to be more detections above the plane than below it; in this survey, around 2/3 of the firm Monoceros Ring detections are in the north. This coincides with the northern detections appearing to be qualitatively denser and broader than their southern counterparts. The maximum of the Galactic warp in the south is also probed in this survey. It is found that these fields do not resemble those in the Canis Major region suggesting that the warp does not change the shape of the colour–magnitude diagram as is witnessed around Canis Major. The origins and morphology of the Monoceros Ring are still elusive primarily due to its enormous extent on the sky. Continued probing of the Galactic Outer Disc is needed before a consensus can be reached on its nature. [ABSTRACT FROM AUTHOR]

We present the results of an Anglo-Australian Telescope (AAT) wide field camera survey of the stars in the Monoceros Ring (MRi) and purported Canis Major (CMa) overdensity in the Galactic longitudes of . Current numerical simulations suggest that both of these structures are the result of a single on-going accretion event, although an alternative solution is that the warped and flared disc of the Galaxy can explain the origin of both of these structures. Our results show that, with regards the MRi, the warped and flared disc is unable to reproduce the locations and strengths of the detections observed around the Galaxy. This supports a non-Galactic origin for this structure. We report eight new detections and two tentative detections of the MRi in this survey. The exact nature of the CMa overdensity is still unresolved, although this survey provides evidence that invoking the Galactic warp is not a sufficient solution when compared with observation. Several fields in this survey are highly inconsistent with the current Galactic disc models that include a warp and flare, to such an extent that explaining their origins with these structures is problematic. We also report that the blue plume stars previously invoked to support the dwarf galaxy hypothesis are unfounded, and associating them with an outer spiral arm is equally problematic. Standard Galactic models are unable to accommodate all the observations of these new structures, leading away from a warped/flared disc explanation for their origins and more toward a non-Galactic source. Additionally, evidence is presented in favour of a detection of the CMa dwarf stream away from the CMa region. As the outer reaches of the Galactic disc continue to be probed, the fascinating structures that are the MRi and CMa overdensity will no doubt continue to inform us of the unique structure and formation of the Milky Way. [ABSTRACT FROM AUTHOR]

Chemical evolution models are presented for the anomalous globular cluster ω Centauri. After demonstrating that the chemical features of ω Cen cannot be reproduced in the framework of the closed-box self-enrichment scenario, we discuss a model in which this cluster is the remnant of a dwarf spheroidal galaxy evolved in isolation and then swallowed by the Milky Way. Both infall of primordial matter and metal-enriched gas outflows have to be considered in order to reproduce the stellar metallicity distribution function, the age–metallicity relation and several abundance ratios. Yet, as long as an ordinary stellar mass function and standard stellar yields are assumed, we fail by far to get the enormous helium enhancement required to explain the blue main sequence (and, perhaps, the extreme horizontal branch) stellar data. Rotating models of massive stars producing stellar winds with large helium excesses at low metallicities have been put forward as promising candidates to solve the ‘helium enigma’ of ω Cen. However, we show that for any reasonable choice of the initial mass function the helium-to-metal enrichment of the integrated stellar population is unavoidably much lower than 70 and conclude that the issue of the helium enhancement in ω Cen still waits for a satisfactory explanation. We briefly speculate upon possible solutions. [ABSTRACT FROM AUTHOR]

An AAT/2dF Spectrograph Survey of low Galactic latitudes targeting the putative Canis Major dwarf galaxy and the (possibly) associated tidal debris of stars known as the Monoceros Ring, covering Galactic coordinates and , has revealed the presence of the Monoceros Ring in the background of the Canis Major dwarf galaxy. This detection resides at a Galactocentric distance of (13.5 ± 0.3 kpc heliocentric), exhibiting a velocity of with a dispersion of , both of these comparable to previous measurements of the Monoceros Ring in nearby fields. This detection highlights the increasing complexity of structure being revealed in recent surveys of the Milky Way thick disc and halo. [ABSTRACT FROM AUTHOR]

I briefly explore some relevant connections and differences between the evolutionary paths of dwarf galaxies and globular clusters. [ABSTRACT FROM PUBLISHER]