SMHASH: Anatomy of the Orphan Stream using RR Lyrae stars

Abstract

Stellar tidal streams provide an opportunity to study the motion and structure of the disrupting galaxy as well as the gravitational potential of its host. Streams around the Milky Way are especially promising as phase space positions of individual stars will be measured by ongoing or upcoming surveys. Nevertheless, it remains a challenge to accurately assess distances to stars farther than 10 kpc from the Sun, where we have the poorest knowledge of the Galaxy's mass distribution. To address this we present observations of 32 candidate RR Lyrae stars in the Orphan tidal stream taken as part of the Spitzer Merger History and Shape of the Galactic Halo (SMHASH) program. The extremely tight correlation between the periods, luminosities, and metallicities of RR Lyrae variable stars in the Spitzer IRAC $3.6\mu \mathrm{m}$ band allows the determination of precise distances to individual stars; the median statistical distance uncertainty to each RR Lyrae star is $2.5\%$. By fitting orbits in an example potential we obtain an upper limit on the mass of the Milky Way interior to 60 kpc of $5.6_{-1.1}^{+1.2}\times 10^{11}{\mathrm{M}}_{\odot }$, bringing estimates based on the Orphan Stream in line with those using other tracers. The SMHASH data also resolve the stream in line--of--sight depth, allowing a new perspective on the internal structure of the disrupted dwarf galaxy. Comparing with N--body models we find that the progenitor had an initial dark halo mass of approximately $3.2\times 10^9{\mathrm{M}}_{\odot }$, placing the Orphan Stream's progenitor amongst the classical dwarf spheroidals.

18 pages, 10 figures. Submitted to MNRAS; comments welcome

References in corpus (25)

• The Gaia mission
• 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
• The Milky Way's circular velocity curve between 4 and 14 kpc from APOGEE data
• Tracing Galaxy Formation with Stellar Halos II: Relating Substructure in Phase- and Abundance-Space to Accretion Histories
• An Orphan in the "Field of Streams"
• "Skinny Milky Way, Please", says Sagittarius
• Detection of a 60 Degree-Long Dwarf Galaxy Debris Stream
• The Galaxy and its stellar halo: insights on their formation from a hybrid cosmological approach
• Globular Cluster Streams as Galactic High-Precision Scales - The Poster Child Palomar 5
• The Cold Dark Matter Halos of Local Group Dwarf Spheroidals
• The shape of the inner Milky Way halo from observations of the Pal 5 and GD-1 stellar streams
• The mechanics of tidal streams
• On the distance of the globular cluster M4 (NGC 6121) using RR Lyrae stars: I. optical and near-infrared Period-Luminosity and Period-Wesenheit relations
• The dependence of convective core overshooting on stellar mass: semi-empirical determination using the diffusive approach with two different element mixtures
• A Tail of Two Populations: Chemo-dynamics of the Sagittarius Stream and Implications for its Original Mass
• Weak Galactic halo--dwarf spheroidal connection from RR Lyrae stars
• On feathers, bifurcations and shells: the dynamics of tidal streams across the mass scale
• Revealing Substructure in the Galactic Halo - The SEKBO RR Lyrae Survey
• The VMC survey - XXVI. Structure of the Small Magellanic Cloud from RR Lyrae stars
• The $>100$ kpc Distant Spur of the Sagittarius Stream and the Outer Virgo Overdensity, as Seen in PS1 RR Lyrae Stars
• The Geometry of Sagittarius Stream from Pan-STARRS1 3$\pi$ RR Lyrae
• Action-space clustering of tidal streams to infer the Galactic potential
• The cold dark matter content of Galactic dwarf spheroidals: no cores, no failures, no problem
• The Outer Halo of the Milky Way as Probed by RR Lyr Variables from the Palomar Transient Facility
• Hubble Space Telescope Proper Motions of Individual Stars in Stellar Streams: Orphan, Sagittarius, Lethe, and the New "Parallel" Stream

Cited by in corpus (14)

• The total mass of the Large Magellanic Cloud from its perturbation on the Orphan stream
• The mass of our Milky Way
• Piercing the Milky Way: an all-sky view of the Orphan Stream
• $S^5$: Probing the Milky Way and Magellanic Clouds potentials with the 6-D map of the Orphan-Chenab stream
• Old-Aged Stellar Population Distance Indicators
• Modelling the Tucana III stream - a close passage with the LMC
• Discovery of distant RR Lyrae stars in the Milky Way using DECam
• The Carnegie RR Lyrae Program: Mid-infrared Period-Luminosity relations of RR Lyrae stars in Reticulum
• The course of the Orphan Stream in the Northern Galactic Hemisphere traced with Gaia DR2
• Milky Way archaeology using RR Lyrae and type II Cepheids I. The Orphan stream in 7D using RR Lyrae stars
• SMHASH: A new mid-infrared RR Lyrae distance determination for the Local Group dwarf spheroidal galaxy Sculptor
• Estimate of the Mass and Radial Profile of the Orphan-Chenab Stream's Dwarf Galaxy Progenitor Using MilkyWay@home
• One Stream or Two -- Exploring Andromeda's North West Stream
• rrlfe: Software for Generating and Applying Metallicity Calibrations for RR Lyrae Variable Stars Across a Wide Range of Phases and Temperatures