The Large Synoptic Survey Telescope and Milky Way Science

TL;DR

The LSST will significantly advance Milky Way science by providing deep, precise photometric and astrometric data, enabling detailed mapping of Galactic structures and dark matter interactions, despite initial survey limitations.

Contribution

This paper highlights the potential of LSST for Galactic astronomy, emphasizing its capabilities and advocating for inclusive survey strategies including the Galactic Plane.

Findings

LSST will map halo structures to 450 kpc, nearly half the distance to Andromeda.

Proper motion measurements will reach 0.2 mas/yr at r=21, enabling detailed kinematic studies.

Deep photometry will detect over a billion stars, revealing fine Galactic structure.

Abstract

The Large Synoptic Survey Telescope (LSST) surveys have initially been optimized to omit the inner part of the Milky Way disk/bar from deep and cadence observations. However it is now clear that the LSST will be powerful for Galactic astronomy and may play a crucial role in continuing to extend the Gaia astrometric catalog until a future satellite, either optical or IR, carries on. LSST will provide metallicities and kinematics for the bulge, and will map halo structures to as distant as 450 kpc, nearly half the distance to the Andromeda galaxy. Thanks to the unprecedented calibration effort for its photometric system, and surprisingly good astrometry (transverse velocity measurements of 0.2 mas/yr at r=21; 1 mas/yr at r=24). LSST will provide photometric abundances and distance constraints for a billion or more Milky Way stars to distances of 450 kpc, and kinematics from proper motions to $\sim100$ kpc. Single observation depths reach $\sim 24$ in the $ugrizy$ bands, while depths at end of mission reach $\sim 27$. Although halo structures such as streams and dwarf galaxies are initially identified by the RR Lyrae and giants, their structure will be fleshed out by the 100$\times$ more abundant dwarfs that will be detected to 100 kpc (single observation) and $\sim 300$ kpc by end of mission. More complete mapping of stream structures may constrain the mass distribution of dark matter and perhaps confirm the interaction of dark matter halos and streams. I also describe the Blanco DECam Bulge Survey, a 200 deg$^2$ LSST pathfinder survey of the bulge in $ugrizy$ using the Dark Energy Camera on the Blanco 4m telescope. The purpose of this article is to encourage active workers on the Milky Way and Local Volume to participate in the LSST project, in particular to urge that the Galactic Plane receive the same cadence and depth coverage as the rest of the extragalactic sky.