The First Distance Constraint on the Renegade High Velocity Cloud Complex WD

Abstract

We present medium-resolution, near-ultraviolet VLT/FLAMES observations of the star USNO-A0600-15865535. We adapt a standard method of stellar typing to our measurement of the shape of the Balmer epsilon absorption line to demonstrates that USNO-A0600-15865535 is a blue horizontal branch star, residing in the lower stellar halo at a distance of 4.4 kpc from the Sun. We measure the H & K lines of singly-ionized calcium and find two isolated velocity components, one originating in the disk, and one associated with high-velocity cloud complex WD. This detection demonstrated that complex WD is closer than ~4.4 kpc and is the first distance constraint on the +100 km/s Galactic complex of clouds. We find that Complex WD is not in corotation with the Galactic disk as has been assumed for decades. We examine a number of scenarios, and find that the most likely is that Complex WD was ejected from the solar neighborhood and is only a few kpc from the Sun.

6 pages, 4 figures, submitted to ApJL

References in corpus (6)

• 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
• Distances to Galactic high-velocity clouds. I. Cohen Stream, complex GCP, cloud g1
• Distances to Galactic high-velocity clouds. Complex C
• An Accurate Distance to High-Velocity Cloud Complex C
• Smith's Cloud: A High-velocity Cloud Colliding with the Milky Way
• Reconstructing Deconstruction: High-Velocity Cloud Distance Through Disruption Morphology

Cited by in corpus (4)

• A new all-sky map of Galactic high-velocity clouds from the 21-cm HI4PI survey
• The Circumgalactic Medium of Milky Way-like Galaxies in the TNG50 Simulation -- II: Cold, Dense Gas Clouds and High-Velocity Cloud Analogs
• Zooming in on the Circumgalactic Medium with GIBLE: Tracing the Origin and Evolution of Cold Clouds
• Distance estimation of the high-velocity cloud Anti-Center Shell