OGHReS: Star formation in the Outer Galaxy II ($\ell = 180^\circ$-$280^\circ$)

TL;DR

This study maps and analyzes over 6000 molecular clumps in the Outer Galaxy, revealing new spiral structures, star formation trends, and velocity discrepancies across surveys, enhancing understanding of galactic star formation regions.

Contribution

It provides a comprehensive catalog of clump velocities and properties in the Outer Galaxy, updates previous data, and uncovers new spiral features and star formation patterns.

Findings

Discovery of a new spiral structure in the Outer Galaxy.

Decreasing $L/M$-ratio indicating less high-mass star formation.

Increased star formation fraction despite lower clump masses.

Abstract

The Outer Galaxy High-Resolution Survey (OGHReS) covers 100 square degrees ($180^\circ < \ell < 280^\circ$) in the (2--1) transitions of three CO-isotopologues. We use the spectra to refine the velocities and physical properties to 6706 \higal\ clumps located in the OGHReS region. In a previous paper, we analysed 3584 clumps between $\ell = 250^\circ$ and $280^\circ$. Here, we cover a further 3122 clumps ($180^\circ < \ell < 250^\circ$) and determine reliable velocities for \withVLSR\ of these, finding good agreement with the previously assigned velocities ($\sim$80 percent within 5 \kms). We update velocities for 288 clumps and provide new values for an additional 411. Combining these with the previous results, we have velocities and physical properties for 6193 clumps (92.3 percent). The \allnonDetections\ non-detections are low surface density clumps or likely contamination by evolved stars and galaxies. Key findings: i) improved correlation between clumps and spiral arm loci, and the discovery of clumps beyond the outer arm supports the existence of a new spiral structure; ii) decreasing trend in the $L/M$-ratio consistent with less high-mass star formation in the outer Galaxy; iii) increase in the star formation fraction (SFF) in the outer Galaxy, suggesting that more clumps are forming stars despite their lower mass; iv) discrepancies in velocity assignments across different surveys that could affect $\sim$10000 clumps, especially in the fourth quadrant.