Catalog of spiral arm Tangents (Galactic Longitudes) in the Milky Way, and the Age Gradient based on various arm tangents

TL;DR

This paper provides an updated catalog of 205 spiral arm tangents in the Milky Way, analyzing their separation from dust lanes to determine an age gradient and relative speeds of arm tracers.

Contribution

It presents an expanded catalog of spiral arm tangents and introduces an analysis of age gradients based on arm tracer separations from dust lanes.

Findings

Age gradient of about 11.3 +/- 2 Myr/kpc across spiral arms

Relative speed of arm tracers away from dust lanes is approximately 87 +/- 10 km/s

Addition of 80 new arm tangents since 2016

Abstract

An updated catalog of 205 observed tangents to the spiral arms (in Galactic longitudes) since 1980 is presented. This represents an addition of 80 arm tangents in 6 years (since 2016). Most arm tangents are observed at telescopes in the radio regime. In this study, the separation of each arm tracer from the dust lane is analyzed to obtain the relative speed away from the dust lane (an age gradient). Each arm tracer is observed to be separated from the dust lane, showing an age gradient of about 11.3 +/- 2 Myr/kpc across the spiral arm; this gives a relative speed away from the dust lane of about 87 +/- 10 km/s.