| 1. |
- Arentsen, A., et al.
(författare)
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The Pristine Inner Galaxy Survey (PIGS) I : tracing the kinematics of metal-poor stars in the Galactic bulge
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966 .- 1745-3925 .- 1745-3933. ; 491:1, s. L11-L16
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Tidskriftsartikel (refereegranskat)abstract
- Our Galaxy is known to contain a central boxy/peanut-shaped bulge, yet the importance of a classical, pressure-supported component within the central part of the Milky Way is still being debated. It should be most visible at low metallicity, a regime that has not yet been studied in detail. Using metallicity-sensitive narrow-band photometry, the Pristine Inner Galaxy Survey (PIGS) has collected a large sample of metal-poor ([Fe/H] < -1.0) stars in the inner Galaxy to address this open question. We use PIGS to trace the metal-poor inner Galaxy kinematics as function of metallicity for the first time. We find that the rotational signal decreases with decreasing [Fe/H], until it becomes negligible for the most metal-poor stars. Additionally, the velocity dispersion increases with decreasing metallicity for -3.0 < [Fe/II] < -0.5, with a gradient of -44 +/- 41un s(-1)dex(-1). These observations may signal a transition between Galactic components of different metallicities and kinematics, a different mapping on to the boxy/peanut-shaped bulge for former disc stars of different metallicities and/or the secular dynamical and gravitational influence of the bar on the pressure-supported component. Our results provide strong constraints on models that attempt to explain the properties of the inner Galaxy.
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| 2. |
- Bellazzini, M., et al.
(författare)
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Globular clusters in the Sagittarius stream Revising members and candidates with Gaia DR2
- 2020
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 636
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Tidskriftsartikel (refereegranskat)abstract
- We reconsider the case for the association of Galactic globular clusters to the tidal stream of the Sagittarius dwarf spheroidal galaxy (Sgr dSph) using Gaia DR2 data. We used RR Lyrae variables to trace the stream in 6D and we selected clusters matching the observed stream in position and velocity. In addition to the clusters residing in the main body of the galaxy (M 54, Ter 8, Ter 7, Arp 2) we confirm the membership of Pal 12 and Whiting 1 to the portion of the trailing arm populated by stars lost during recent perigalactic passages. NGC 2419, NGC 5634, and NGC 4147 are very interesting candidates, possibly associated with more ancient wraps of the Sagittarius stream. With the exception of M 54, which lies within the stellar nucleus of the galaxy, we note that all these clusters are found in the trailing arm of the stream. The selected clusters are fully consistent with the [Fe/H] versus [Mg/Fe], [Ca/Fe] patterns and the age-metallicity relation displayed by field stars in the main body of Sgr dSph.
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| 3. |
- Bellazzini, Michele, et al.
(författare)
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Young stars raining through the galactic halo : the nature and orbit of price-whelan 1
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 490:2, s. 2588-2598
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Tidskriftsartikel (refereegranskat)abstract
- We present radial velocities for five member stars of the recently discovered young (age similar or equal to 100-150 Myr) stellar system Price-Whelan 1 (PW1), which is located far away in the Galactic Halo (D similar or equal to 29 kpc, Z similar or equal to 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 HI 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 similar or equal to 25 km s(-1) and similar or equal to 10 deg similar or equal to 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.
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| 4. |
- de Salas, Pablo Fernández, et al.
(författare)
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On the estimation of the local dark matter density using the rotation curve of the Milky Way
- 2019
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP PUBLISHING LTD. - 1475-7516. ; :10
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Tidskriftsartikel (refereegranskat)abstract
- The rotation curve of the Milky Way is commonly used to estimate the local dark matter density rho(DM,circle dot). However, the estimates are subject to the choice of the distribution of baryons needed in this type of studies. In this work we explore several Galactic mass models that differ in the distribution of baryons and dark matter, in order to determine rho(DM,circle dot). For this purpose we analyze the precise circular velocity curve measurement of the Milky Way up to similar to 25 kpc from the Galactic centre obtained from Gaia DR2 [1]. We find that the estimated value of rho(DM,circle dot) stays robust to reasonable changes in the spherical dark matter halo. However, we show that rho(DM,circle dot) is affected by the choice of the model for the underlying baryonic components. In particular, we find that rho(DM,circle dot) is mostly sensitive to uncertainties in the disk components of the Galaxy. We also show that, when choosing one particular baryonic model, the estimate of rho(DM,circle dot) has an uncertainty of only about 10% of its best-fit value, but this uncertainty gets much bigger when we also consider the variation of the baryonic model. In particular, the rotation curve method does not allow to exclude the presence of an additional very thin component, that can increase rho(DM,circle dot) by more than a factor of 8 (the thin disk could even be made of dark matter). Therefore, we conclude that exclusively using the rotation curve of the Galaxy is not enough to provide a robust estimate of rho(DM,circle dot). For all the models that we study without the presence of an additional thin component, our resulting estimates of the local dark matter density take values in the range rho(DM,circle dot) similar or equal to 0.3-0.4 GeV/cm(3), consistent with many of the estimates in the literature.
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| 5. |
- Fantin, Nicholas J., et al.
(författare)
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The Canada-France Imaging Survey : Reconstructing the Milky Way Star Formation History from Its White Dwarf Population
- 2019
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 887:2
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Tidskriftsartikel (refereegranskat)abstract
- As the remnants of stars with initial masses less than or similar to 8M(circle dot), white dwarfs contain valuable information on the formation histories of stellar populations. In this paper, we use deep, high-quality, u-band photometry from the Canada-France Imaging Survey, griz photometry from Pan-STARRS1, as well as proper motions from Gaia DR2, to select 25,156 white dwarf candidates over similar to 4500 deg(2) using a reduced proper motion diagram. We develop a new white dwarf population synthesis code that returns mock observations of the Galactic field white dwarf population for a given star formation history, while simultaneously taking into account the geometry of the Milky Way (MW), survey parameters, and selection effects. We use this model to derive the star formation histories of the thin disk, thick disk, and stellar halo. Our results show that the MW disk began forming stars (11.3 +/- 0.5) Gyr ago, with a peak rate of (8.8 +/- 1.4) M-circle dot yr(-1) at (9.8 +/- 0.4) Gyr, before a slow decline to a constant rate until the present day-consistent with recent results suggesting a merging event with a satellite galaxy. Studying the residuals between the data and best-fit model shows evidence for a slight increase in star formation over the past 3 Gyr. We fit the local fraction of helium-atmosphere white dwarfs to be (21 +/- 3)%. Incorporating this methodology with data from future wide-field surveys such as the Large Synoptic Survey Telescope, Euclid, The Cosmological Advanced Survey Telescope for Optical and ultraviolet Research, and the Wide Field Infrared Survey Telescope should provide an unprecedented view into the formation of the MW at its earliest epoch through its white dwarfs.
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| 6. |
- Fernández-Alvar, Emma, et al.
(författare)
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The Pristine survey XIII : uncovering the very metal-poor tail of the thin disc
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 508:1, s. 1509-1525
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Tidskriftsartikel (refereegranskat)abstract
- We evaluate the rotational velocity of stars observed by the Pristine survey towards the Galactic anticentre spanning a wide range of metallicities from the extremely metal-poor regime ([Fe/H] < −3) to nearly solar metallicity. In the Galactic anticentre direction, the rotational velocity (Vφ) is similar to the tangential velocity in the galactic longitude direction (V). This allows us to estimate Vφ from Gaia early data release 3 (Gaia EDR3) proper motions for stars without radial velocity measurements. This substantially increases the sample of stars in the outer disc with estimated rotational velocities. Our stellar sample towards the anticentre is dominated by a kinematical thin disc with a mean rotation of ∼−220 km s−1. However, our analysis reveals the presence of more stellar substructures. The most intriguing is a well-populated extension of the kinematical thin disc down to [Fe/H] ∼ −2 . A scarcer fast-rotating population reaching the extremely metal-poor regime down to [Fe/H] ∼ −3.5 is also detected but without statistical significance to unambiguously state whether this is the extremely metal-poor extension of the thin disc or the high-rotating tail of hotter structures (like the thick disc or the halo). In addition, a more slowly rotating kinematical thick disc component is also required to explain the observed V distribution at [Fe/H] > −1.5 . Furthermore, we detect signatures of a ‘heated disc’, the so-called Splash, at metallicities higher than ∼−1.5. Finally, at [Fe/H] < −1.5 our anticentre sample is dominated by a kinematical halo with a net prograde motion.
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| 7. |
- Ibata, Rodrigo A., et al.
(författare)
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Identification of the long stellar stream of the prototypical massive globular cluster ω Centauri
- 2019
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Ingår i: Nature Astronomy. - : Springer Science and Business Media LLC. - 2397-3366. ; 3:7, s. 667-672
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Tidskriftsartikel (refereegranskat)abstract
- Omega Centauri (omega Cen) is the Milky Way's most massive globular cluster, and has long been suspected of being the remnant core of an accreted dwarf galaxy. If this scenario is correct, omega Cen should be tidally limited and tidal debris should be spread along its orbit. Here we use N-body simulations to show that the recently discovered 'Fimbulthul' structure is the long-sought-for tidal stream of omega Cen, extending up to 28 degrees from the cluster. Follow-up high-resolution spectroscopy of five stream stars shows that they are closely grouped in velocity, and have metallicities consistent with having originated in that cluster. Informed by our N-body simulations, we devise a selection filter that we apply to Gaia mission data to also uncover the stream in the highly contaminated and crowded field within 10 degrees of omega Cen. Further modelling of the stream may help to constrain the dynamical history of the dwarf galaxy progenitor of this disrupting system and guide future searches for its remnant stars in the Milky Way.
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| 8. |
- Ibata, Rodrigo, et al.
(författare)
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A Panoramic Landscape of the Sagittarius Stream in Gaia DR2 Revealed with the STREAMFINDER Spyglass
- 2020
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Ingår i: Astrophysical Journal Letters. - : American Astronomical Society. - 2041-8205 .- 2041-8213. ; 891:1
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Tidskriftsartikel (refereegranskat)abstract
- We present the first full six-dimensional panoramic portrait of the Sagittarius stream, obtained by searching for wide stellar streams in the Gaia DR2 data set with the STREAMFINDER algorithm. We use the kinematic behavior of the sample to devise a selection of Gaia RR Lyrae, providing excellent distance measurements along the stream. The proper motion data are complemented with radial velocities from public surveys. We find that the global morphological and kinematic properties of the Sagittarius stream are still reasonably well reproduced by the simple Law & Majewski model (LM10), although the model overestimates the leading arm and trailing arm distances by up to similar to 15%. The sample newly reveals the leading arm of the Sagittarius stream as it passes into very crowded regions of the Galactic disk toward the Galactic anticenter direction. Fortuitously, this part of the stream is almost exactly at the diametrically opposite location from the Galactic center to the progenitor, which should allow an assessment of the influence of dynamical friction and self-gravity in a way that is nearly independent of the underlying Galactic potential model.
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| 9. |
- Ibata, Rodrigo A., et al.
(författare)
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The Streams of the Gaping Abyss : A Population of Entangled Stellar Streams Surrounding the Inner Galaxy
- 2019
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 872:2
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Tidskriftsartikel (refereegranskat)abstract
- We present the discovery of a large population of stellar streams that surround the inner Galaxy, found in the Gaia DR2 catalog using the new STREAMFINDER algorithm. Here we focus on the properties of eight new high-significance structures found at heliocentric distances between 1 and 10 kpc and at Galactic latitudes vertical bar b vertical bar > 20 degrees, named Slidr, Sylgr, Ylgr, Fimbulthul, Svol, Fjorm, Gjoll, and Leiptr. Spectroscopic measurements of seven of the streams confirm the detections, which are based on Gaia astrometry and photometry alone, and show that these streams are predominantly metal-poor. The sample possesses diverse orbital properties, although most of the streams appear to be debris of inner-halo globular clusters. Many more candidate streams are visible in our maps but require follow-up spectroscopy to confirm their nature. We also explain in detail the workings of the algorithm and gauge the incidence of false detections by running the algorithm on a smooth model of the Gaia catalog.
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| 10. |
- Ibata, Rodrigo, et al.
(författare)
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Charting the Galactic Acceleration Field. I. A Search for Stellar Streams with Gaia DR2 and EDR3 with Follow-up from ESPaDOnS and UVES
- 2021
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 914:2
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Tidskriftsartikel (refereegranskat)abstract
- We present maps of the stellar streams detected in the Gaia Data Release 2 (DR2) and Early Data Release 3 (EDR3) catalogs using the STREAMFINDER algorithm. We also report the spectroscopic follow-up of the brighter DR2 stream members obtained with the high-resolution CFHT/ESPaDOnS and VLT/UVES spectrographs as well as with the medium-resolution NTT/EFOSC2 spectrograph. Two new stellar streams that do not have a clear progenitor are detected in DR2 (named Hrid and Gunnthra), and seven are detected in EDR3 (named Gaia-6 to Gaia-12). Several candidate streams are also identified. The software also finds very long tidal tails associated with the 15 globular clusters: NGC 288, NGC 1261, NGC 1851, NGC 2298, NGC 2808, NGC 3201, M68, omega Cen, NGC 5466, Palomar 5, M5, NGC 6101, M92, NGC 6397, and NGC 7089. These stellar streams will be used in subsequent contributions in this series to chart the properties of the Galactic acceleration field on similar to 100 pc to similar to 100 kpc scales.
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