skip to main content

A Young, Low-density Stellar Stream in the Milky Way Disk: Theia 456
Abstract

Our view of the variety of stellar structures pervading the local Milky Way has been transformed by the application of clustering algorithms to the Gaia catalog. In particular, several stellar streams have been recently discovered that are comprised of hundreds to thousands of stars and span several hundred parsecs. We analyze one such structure, Theia 456, a low-density stellar stream extending nearly 200 pc and 20° across the sky. By supplementing Gaia astrometric data with spectroscopic metallicities from Large Sky Area Multi-Object Fiber Spectroscopic Telescope and photometric rotation periods from the Zwicky Transient Facility and the Transiting Exoplanet Survey Satellite, we establish Theia 456's radial velocity coherence, and we find strong evidence that members of Theia 456 have a common age (≃175 Myr), common dynamical origin, and formed from chemically homogeneous prestellar material ([Fe/H] = −0.07 dex). Unlike well-known stellar streams in the Milky Way, which are in its halo, Theia 456 is firmly part of the thin disk. If our conclusions about Theia 456 can be applied to even a small fraction of the remaining ≃8300 independent structures in the Theia catalog, such low-density stellar streams may be ubiquitous. We comment on the implications this has for the more »

Authors:
; ; ; ; ; ;
Publication Date:
NSF-PAR ID:
10367258
Journal Name:
The Astronomical Journal
Volume:
163
Issue:
6
Page Range or eLocation-ID:
Article No. 275
ISSN:
0004-6256
Publisher:
DOI PREFIX: 10.3847
Sponsoring Org:
National Science Foundation
##### More Like this
1. ABSTRACT

We introduce the southern stellar stream spectroscopy survey (S5), an on-going program to map the kinematics and chemistry of stellar streams in the southern hemisphere. The initial focus of S5 has been spectroscopic observations of recently identified streams within the footprint of the dark energy survey (DES), with the eventual goal of surveying streams across the entire southern sky. Stellar streams are composed of material that has been tidally striped from dwarf galaxies and globular clusters and hence are excellent dynamical probes of the gravitational potential of the Milky Way, as well as providing a detailed snapshot of its accretion history. Observing with the 3.9 m Anglo-Australian Telescope’s 2-degree-Field fibre positioner and AAOmega spectrograph, and combining the precise photometry of DES DR1 with the superb proper motions from Gaia DR2, allows us to conduct an efficient spectroscopic survey to map these stellar streams. So far S5 has mapped nine DES streams and three streams outside of DES; the former are the first spectroscopic observations of these recently discovered streams. In addition to the stream survey, we use spare fibres to undertake a Milky Way halo survey and a low-redshift galaxy survey. This paper presents an overview of the S5 program,more »

2. Abstract

Stellar mass is a fundamental parameter that is key to our understanding of stellar formation and evolution, as well as the characterization of nearby exoplanet companions. Historically, stellar masses have been derived from long-term observations of visual or spectroscopic binary star systems. While advances in high-resolution imaging have enabled observations of systems with shorter orbital periods, measurements of stellar masses remain challenging, and relatively few have been precisely measured. We present a new statistical approach to measuring masses for populations of stars. Using Gaia astrometry, we analyze the relative orbital motion of >3800 wide binary systems comprising low-mass stars to establish a mass–magnitude relation in the GaiaGRPband spanning the absolute magnitude range 14.5 >$MGRP$> 4.0, corresponding to a mass range of 0.08MM≲ 1.0M. This relation is directly applicable to >30 million stars in the Gaia catalog. Based on comparison to existing mass–magnitude relations calibrated forKsmagnitudes from the Two Micron All Sky Survey, we estimate that the internal precision of our mass estimates is ∼10%. We use this relation to estimate masses for a volume-limited sample of ∼18,200 stars within 50 pc of the Sun and the present-day field mass function for stars withM≲ 1.0M, which wemore »

3. Abstract We report the kinematic, orbital, and chemical properties of 12 stellar streams with no evident progenitors using line-of-sight velocities and metallicities from the Southern Stellar Stream Spectroscopic Survey ( S 5 ), proper motions from Gaia EDR3, and distances derived from distance tracers or the literature. This data set provides the largest homogeneously analyzed set of streams with full 6D kinematics and metallicities. All streams have heliocentric distances between ∼10 and 50 kpc. The velocity and metallicity dispersions show that half of the stream progenitors were disrupted dwarf galaxies (DGs), while the other half originated from disrupted globular clusters (GCs), hereafter referred to as DG and GC streams. Based on the mean metallicities of the streams and the mass–metallicity relation, the luminosities of the progenitors of the DG streams range between those of Carina and Ursa Major I (−9.5 ≲ M V ≲ −5.5). Four of the six GC streams have mean metallicities of [Fe/H] < −2, more metal poor than typical Milky Way (MW) GCs at similar distances. Interestingly, the 300S and Jet GC streams are the only streams on retrograde orbits in our dozen-stream sample. Finally, we compare the orbital properties of the streams with known DGsmore »
4. Luminous hot stars ( M K s  ≲ 0 mag and T eff  ≳ 8000 K) dominate the stellar energy input to the interstellar medium throughout cosmological time, are used as laboratories to test theories of stellar evolution and multiplicity, and serve as luminous tracers of star formation in the Milky Way and other galaxies. Massive stars occupy well-defined loci in colour–colour and colour–magnitude spaces, enabling selection based on the combination of Gaia EDR3 astrometry and photometry and 2MASS photometry, even in the presence of substantive dust extinction. In this paper we devise an all-sky sample of such luminous OBA-type stars, which was designed to be complete rather than very pure, providing targets for spectroscopic follow-up with the SDSS-V survey. To estimate the purity and completeness of our catalogue, we derive stellar parameters for the stars in common with LAMOST DR6 and we compare the sample to other O and B-type star catalogues. We estimate ‘astro-kinematic’ distances by combining parallaxes and proper motions with a model for the expected velocity and density distribution of young stars; we show that this adds useful constraints on the distances and therefore luminosities of the stars. With these distances we map the spatial distribution of a moremore »
5. ABSTRACT

We measure the enclosed Milky Way mass profile to Galactocentric distances of ∼70 and ∼50 kpc using the smooth, diffuse stellar halo samples of Bird et al. The samples are Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and Sloan Digital Sky Survey/Sloan Extension for Galactic Understanding and Exploration (SDSS/SEGUE) K giants (KG) and SDSS/SEGUE blue horizontal branch (BHB) stars with accurate metallicities. The 3D kinematics are available through LAMOST and SDSS/SEGUE distances and radial velocities and Gaia DR2 proper motions. Two methods are used to estimate the enclosed mass: 3D spherical Jeans equation and Evans et al. tracer mass estimator (TME). We remove substructure via the Xue et al. method based on integrals of motion. We evaluate the uncertainties on our estimates due to random sampling noise, systematic distance errors, the adopted density profile, and non-virialization and non-spherical effects of the halo. The tracer density profile remains a limiting systematic in our mass estimates, although within these limits we find reasonable agreement across the different samples and the methods applied. Out to ∼70 and ∼50 kpc, the Jeans method yields total enclosed masses of 4.3 ± 0.95 (random) ±0.6 (systematic) × 1011 M⊙ and 4.1 ± 1.2 (random) ±0.6 (systematic) × 1011 M⊙ for the KG and BHB stars, respectively.more »