Chemical tagging can work: Identification of stellar phase-space structures purely by chemical-abundance similarity

TL;DR

This study demonstrates that chemical tagging using high-precision abundance measurements can effectively identify stellar structures in phase space without positional data, confirming the viability of chemical tagging for galactic archaeology.

Contribution

It is the first survey-scale project to identify phase-space structures solely through chemical-abundance similarity, validating the precision of The Cannon's measurements.

Findings

Clusters in chemical space correspond to phase-space clusters.

Successfully recovered known stellar groups.

Identified new potential stellar structures.

Abstract

Chemical tagging promises to use detailed abundance measurements to identify spatially separated stars that were in fact born together (in the same molecular cloud), long ago. This idea has not yielded much practical success, presumably because of the noise and incompleteness in chemical-abundance measurements. We have succeeded in substantially improving spectroscopic measurements with The Cannon, which has now delivered 15 individual abundances for ~100,000 stars observed as part of the APOGEE spectroscopic survey, with precisions around 0.04 dex. We test the chemical-tagging hypothesis by looking at clusters in abundance space and confirming that they are clustered in phase space. We identify (by the k-means algorithm) overdensities of stars in the 15-dimensional chemical-abundance space delivered by The Cannon, and plot the associated stars in phase space. We use only abundance-space information (no positional information) to identify stellar groups. We find that clusters in abundance space are indeed clusters in phase space. We recover some known phase-space clusters and find other interesting structures. This is the first-ever project to identify phase-space structures at survey-scale by blind search purely in abundance space; it verifies the precision of the abundance measurements delivered by The Cannon; the prospects for future data sets appear very good.