Modelling the stellar halo with RR-Lyrae stars

Abstract

A seven-parameter distribution function (DF) is fitted to $20000$ RR-Lyrae stars for which only astrometric data are available. The observational data are predicted by the DF in conjunction with the gravitational potential of a self-consistent model Galaxy defined by DFs for the dark halo, the bulge and a four-component disc. Tests of the technique developed to deal with missing line-of-sight velocities show that adding such velocities tightens constraints on the DF only slightly. The recovered model of the RR-Lyrae population confirms that the population is flattened and has a strongly radially biased velocity distribution. At large radii its density profile tends to $\rho \sim r^{-4.5}$ but no power law provides a good fit inside the solar sphere. The model is shown to provide an excellent fit to the data for stars brighter than $r=16.5$ but at certain longitudes it predicts too few faint stars at Galactocentric radii $\sim20\mbox{kpc}$, possibly signalling that the halo is not axisymmetric. The DF is used to predict the velocity distribution of BHB stars for which space velocities are available. The $z$ components are predicted successfully but too much anisotropy in the $v_R{v}_{\varphi }$ plane is expected.

arXiv comment19 pages, 16 figures. Accepted by MNRAS

References in corpus (48)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• emcee: The MCMC Hammer
• Gaia Data Release 2. Summary of the contents and survey properties
• The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package
• The Galaxy in Context: Structural, Kinematic and Integrated Properties
• The merger that led to the formation of the Milky Way's inner stellar halo and thick disk
• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: I. Morphology of the Sagittarius Core and Tidal Arms
• Co-formation of the Galactic disc and the stellar halo
• AGAMA: Action-based galaxy modelling architecture
• Evidence for Two Early Accretion Events That Built the Milky Way Stellar Halo
• Structure and Kinematics of the Stellar Halos and Thick Disks of the Milky Way Based on Calibration Stars from SDSS DR7
• The accretion origin of the Milky Way's stellar halo
• The Present and Future Mass of the Milky Way Halo
• Galactic Rotation and Solar Motion from Stellar Kinematics
• The Milky Way stellar halo out to 40 kpc : Squashed, broken but smooth
• The Biggest Splash
• Proper motions and dynamics of the Milky Way globular cluster system from Gaia DR2
• Substructure revealed by RR Lyraes in SDSS Stripe 82
• Precession of the Sagittarius stream
• The Shape and Profile of the Milky Way Halo as Seen by the CFHT Legacy Survey
• Quantifying Kinematic Substructure in the Milky Way's Stellar Halo
• Machine-Learned Identification of RR Lyrae Stars from Sparse, Multi-band Data: the PS1 Sample
• The number and size of subhalo-induced gaps in stellar streams
• The total stellar halo mass of the Milky Way
• Piercing the Milky Way: an all-sky view of the Orphan Stream
• The radial profile and flattening of the Milky Way's stellar halo to $80$kpc from the SEGUE K-giant Survey
• Dynamical modeling of tidal streams
• Exploring the Variable Sky with LINEAR. II. Halo Structure and Substructure Traced by RR Lyrae Stars to 30 kpc
• Chemo-kinematics of the $Gaia$ RR Lyrae: the halo and the disc
• The Gravitational Force Field of the Galaxy Measured From the Kinematics of RR Lyrae in Gaia
• The Halo's Ancient Metal-Rich Progenitor Revealed with BHB Stars
• Galactic kinematics and dynamics from RAVE stars
• Action-based distribution functions for spheroidal galaxy components
• The first all-sky view of the Milky Way stellar halo with Gaia+2MASS RR Lyrae
• A centrally heated dark halo for our Galaxy
• Characterising stellar halo populations I: An extended distribution function for halo K giants
• The distribution function of the Galaxy's dark halo
• Anisotropy of the Milky Way's stellar halo using K giants from LAMOST and $Gaia$
• Self-consistent flattened isochrone models
• The Profile of the Galactic Halo from Pan-STARRS1 3$\pi$ RR Lyrae
• Constraints on the assembly history of the Milky Way's smooth, diffuse stellar halo from the metallicity-dependent, radially-dominated velocity anisotropy profiles probed with K giants and BHB stars using LAMOST, SDSS/SEGUE, and Gaia
• The Galactic Thick Disc density profile traced with RR Lyrae stars
• Analysing surveys of our Galaxy -- II. Determining the potential
• A skewer survey of the Galactic halo from deep CFHT and INT images
• Analysing surveys of our Galaxy I: basic astrometric data
• Modelling the Milky Way's globular cluster system
• Identifying Galactic Halo Substructure in 6D Phase-space Using $\sim$13,000 LAMOST K Giants
• Discy dwarf disruption and the shape of the Galactic halo

Cited by in corpus (2)

• Self-consistent models of our Galaxy
• Influence of the Gaia-Sausage-Enceladus on the density shape of the Galactic stellar halo revealed by halo K giants from the LAMOST survey