Mapping the Northern Galactic Disk Warp with Classical Cepheids

TL;DR

This study provides an updated 3D map of the Milky Way's northern Galactic disk warp using classical Cepheids, revealing a prominent warp with larger amplitude and associated vertical motions, enhancing understanding of Galactic structure.

Contribution

It introduces new Cepheid data covering the northern warp, refines the warp's parameters, and maps vertical velocities, offering detailed insights into Galactic disk dynamics.

Findings

Northern warp is more prominent with ~10% larger amplitude.

Cepheids in the warp show vertical velocities of 10-20 km/s.

Large-scale vertical motions correlate with warp structure.

Abstract

We present an updated three dimensional map of the Milky Way based on a sample of 2431 classical Cepheid variable stars, supplemented with about 200 newly detected classical Cepheids from the OGLE survey. The new objects were discovered as a result of a dedicated observing campaign of the ~280 square degree extension of the OGLE footprint of the Galactic disk during 2018-2019 observing seasons. These regions cover the main part of the northern Galactic warp that has been deficient in Cepheids so far. We use direct distances to the sample of over 2390 classical Cepheids to model the distribution of the young stellar population in the Milky Way and recalculate the parameters of the Galactic disk warp. Our data show that its northern part is very prominent and its amplitude is ~10% larger than that of the southern part. By combining Gaia astrometric data with the Galactic rotation curve and distances to Cepheids from our sample, we construct a map of the vertical component of the velocity vector for all Cepheids in the Milky Way disk. We find large-scale vertical motions with amplitudes of 10-20 km/s, such that Cepheids located in the northern warp exhibit large positive vertical velocity (toward the north Galactic pole), whereas those in the southern warp - negative vertical velocity (toward the south Galactic pole).