A Pristine-UNIONS view on the Galaxy: Kinematics of the distant spur feature of the Sagittarius stream traced by Blue Horizontal Branch stars

Abstract

Providing a detailed picture of the Sagittarius (Sgr) stream offers important constraints on the build-up of the Galactic halo as well as its gravitational potential at large radii. While several attempts have been made to model the structure of the Sgr stream, no model has yet been able to match all the features observed for the stream. Moreover, for several of these features, observational characterisation of their properties is rather limited, particularly at large distances. The aim of this work is to investigate the kinematics of the Sgr stream outermost spur feature using blue horizontal branch (BHB) stars. Candidate BHB stars were selected by combining two approaches; one capitalising on Pan-STARRS1 3$\Pi$ griz and u photometry taken as part of UNIONS, the other using Pristine Survey CaHK and SDSS ugr photometry. Follow-up optical spectra are obtained using ESO/VLT/FORS2 to confirm their BHB nature and obtain line-of-sight (LOS) velocities. Of our 25 candidates, 20 stars can be confirmed as bona fide BHB stars. Their LOS velocities, together with the 3D positions of these stars qualitatively match well with Sgr model predictions and trace the outer apocentre of the trailing arm and its spur feature very nicely. The quantitative offsets that are found between our data and the different models can be used to provide information about the Galactic gravitational potential at large distances. We present a first, tentative, analysis in this direction, showing that the model of Vasiliev et al. (2021) would provide better agreement with our observations if the enclosed mass of the Milky Way within 100 kpc were lowered to $(5.3\pm 0.4)\times 10^{11}$ M${}_{\odot }$ (versus $(5.6\pm 0.4)\times 10^{11}$ M${}_{\odot }$). Our selection of BHB stars provides a new view on the outermost structure in 3D positions and LOS velocities of the Sgr debris.

21 pages, 12 figures, submitted to A&A, abridged abstract

References in corpus (60)

• Array Programming with NumPy
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Gaia Data Release 3: Summary of the content and survey properties
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• The mass distribution and gravitational potential of the Milky Way
• astroquery: An Astronomical Web-Querying Package in Python
• The Milky Way's Circular Velocity Curve to 60 kpc and an Estimate of the Dark Matter Halo Mass from Kinematics of ~2400 SDSS Blue Horizontal Branch Stars
• Euclid. I. Overview of the Euclid mission
• The SEGUE Stellar Parameter Pipeline. I. Description and Initial Validation Tests
• Gaia EDR3 view on Galactic globular clusters
• Gaia Early Data Release 3 -- Catalogue validation
• Evidence from the H3 Survey that the Stellar Halo is Entirely Comprised of Substructure
• Accurate distances to Galactic globular clusters through a combination of Gaia EDR3, HST and literature data
• The SEGUE Stellar Parameter Pipeline. II. Validation with Galactic Globular and Open Clusters
• Tango for three: Sagittarius, LMC, and the Milky Way
• The Eighteenth Data Release of the Sloan Digital Sky Surveys: Targeting and First Spectra from SDSS-V
• Gaia Data Release 3: Analysis of RVS spectra using the General Stellar Parametriser from spectroscopy
• "Skinny Milky Way, Please", says Sagittarius
• Gaia Data Release 3: Astrophysical parameters inference system (Apsis) I -- methods and content overview
• Globular Cluster Streams as Galactic High-Precision Scales - The Poster Child Palomar 5
• The Mass Profile of the Galaxy to 80 kpc
• Overview of the DESI Milky Way Survey
• Quantifying the impact of the Large Magellanic Cloud on the structure of the Milky Way's dark matter halo using Basis Function Expansions
• Detection of the Milky Way reflex motion due to the Large Magellanic Cloud infall
• $S^5$: Probing the Milky Way and Magellanic Clouds potentials with the 6-D map of the Orphan-Chenab stream
• The Canada-France Imaging Survey: First results from the u-band component
• Kinematics of Antlia 2 and Crater 2 from The Southern Stellar Stream Spectroscopic Survey (S5)
• Touching The Void: A Striking Drop in Stellar Halo Density Beyond 50 kpc
• The Circular Velocity Curve of the Milky Way from 5 to 25 kpc using luminous red giant branch star
• The Canada-France Imaging Survey: Reconstructing the Milky Way Star Formation History from its White Dwarf Population
• The $>100$ kpc Distant Spur of the Sagittarius Stream and the Outer Virgo Overdensity, as Seen in PS1 RR Lyrae Stars
• Predicted Extension of the Sagittarius Stream to the Milky Way Virial Radius
• The Geometry of Sagittarius Stream from Pan-STARRS1 3$\pi$ RR Lyrae
• The Rotation Curve, Mass Distribution and Dark Matter Content of the Milky Way from Classical Cepheids
• The effect of the deforming dark matter haloes of the Milky Way and the Large Magellanic Cloud on the Orphan-Chenab stream
• An all-sky proper motion map of the Sagittarius stream using Gaia DR2
• VLT/FORS spectroscopy of faint cataclysmic variables discovered by the Sloan Digital Sky Survey
• Full 5D characterisation of the Sagittarius stream with Gaia DR2 RR Lyrae
• A panoramic landscape of the Sagittarius stream in Gaia DR2 revealed with the STREAMFINDER spyglass
• Bayesian Mass Estimates of the Milky Way II: The dark and light sides of parameter assumptions
• Photometric metallicity and distance estimates for $\sim$ 136,000 RR Lyrae stars from Gaia DR3
• The Pristine survey -- XXIII. Data Release 1 and an all-sky metallicity catalogue based on Gaia DR3 BP/RP spectro-photometry
• Milky Way total Mass derived by Rotation Curve and Globular Cluster kinematics from Gaia EDR3
• Milky Way Mass with K Giants and BHB Stars Using LAMOST, SDSS/SEGUE, and Gaia: 3D Spherical Jeans Equation and Tracer Mass Estimator
• The Sagittarius stream in Gaia eDR3 and the origin of the bifurcations
• Bayesian Mass Estimates of the Milky Way: including measurement uncertainties with hierarchical Bayes
• The hidden past of M92: Detection and characterization of a newly formed 17° long stellar stream using the Canada-France Imaging Survey
• The stellar halo of the Milky Way traced by blue horizontal-branch stars in the Subaru Hyper Suprime-Cam Survey
• Mapping the anisotropic Galactic stellar halo with Blue Horizontal Branch stars
• The Milky Way's circular velocity curve and its constraint on the Galactic mass with RR Lyrae stars
• The Pristine survey -- VII. A cleaner view of the Galactic outer halo using blue horizontal branch stars
• Identification of Sagittarius stream members in Angular Momentum space with Gaussian mixture techniques
• To the Galactic Virial Radius with Hyper Suprime-Cam
• Milky Way archaeology using RR Lyrae and type II Cepheids II. High velocity RR Lyrae stars, and mass of the Milky Way
• A LAMOST BHB Catalog and Kinematics Therein I: Catalog and Halo Properties
• Classifying globular clusters and applying them to estimate the mass of the Milky Way
• Uncovering fossils of the distant Milky Way with UNIONS: NGC 5466 and its stellar stream
• Value-added catalog of M-giant stars in LAMOST DR9
• The SDSS-Gaia View of the Color-Magnitude Relation for Blue Horizontal-branch Stars
• Identifying the possible ex-situ origin of the globular clusters of the Milky Way: A kinematic study

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