Interstellar Krypton Abundances: The Detection of Kiloparsec-scale Differences in Galactic Nucleosynthetic History

TL;DR

This study measures krypton-to-hydrogen ratios across multiple sight lines in the Milky Way, revealing a kiloparsec-scale variation linked to the galaxy's nucleosynthetic history and possibly related to the Gould Belt's formation.

Contribution

It provides the first detailed analysis of interstellar krypton abundances across different galactic regions, highlighting large-scale variations and their potential origins.

Findings

Kr/H ratios are uniform within 5900 pc of the Sun.

An elevated Kr/H ratio is observed in a specific annulus between 600 and 2500 pc.

The annulus shows a decrease in N/O ratio, indicating nucleosynthetic effects.

Abstract

We present an analysis of Kr I 1236 line measurements from 50 sight lines in the Hubble Space Telescope Space Telescope Imaging Spectrograph and Goddard High Resolution Spectrograph data archives that have sufficiently high resolution and signal-to-noise ratio to permit reliable krypton-to-hydrogen abundance ratio determinations. The distribution of Kr/H ratios in this sample is consistent with a single value for the ISM within 5900 pc of the Sun, log(Kr/H) = -9.02+/-0.02, apart from a rough annulus from between about 600 and 2500 pc distant. The Kr/H ratio toward stars within this annulus is elevated by approximately 0.11 dex, similar to previously noted elevations of O/H and Cu/H gas-phase abundances beyond about 800 pc. A significant drop in the gas-phase N/O ratio in the same region suggests that this is an artifact of nucleosynthetic history. Since the physical scale of the annulus' inner edge is comparable to the radius of the Gould Belt and the outer limit of heliocentric distances where the D/H abundance ratio is highly variable, these phenomena may be related to the Gould Belt's origins.