Dense CO in Mrk 71-A: Superwind Suppressed in a Young Super Star Cluster

TL;DR

This study detects a compact molecular cloud associated with a young super star cluster in NGC 2366, showing that energy-driven superwinds are suppressed, which may influence ionizing radiation escape.

Contribution

It provides the first detailed molecular gas observations of Mrk 71-A, demonstrating suppressed superwind feedback and its implications for star formation and ionizing radiation escape.

Findings

Molecular cloud mass ~10^5 M_sun co-located with SSC

Superwind feedback is momentum-driven, not energy-driven

High-density conditions inhibit energy-driven feedback

Abstract

We report the detection of CO(J=2-1) coincident with the super star cluster (SSC) Mrk 71-A in the nearby Green Pea analog galaxy, NGC 2366. Our NOEMA observations reveal a compact, ~7 pc, molecular cloud whose mass (10^5 M_sun) is similar to that of the SSC, consistent with a high star-formation efficiency, on the order of 0.5. There are two, spatially distinct components separated by 11 km/s. If expanding, these could be due to momentum-driven, stellar wind feedback. Alternatively, we may be seeing the remnant infalling, colliding clouds responsible for triggering the SSC formation. The kinematics are also consistent with a virialized system. These extreme, high-density, star-forming conditions inhibit energy-driven feedback; the co-spatial existence of a massive, molecular cloud with the SSC supports this scenario, and we quantitatively confirm that any wind-driven feedback in Mrk 71-A is momentum-driven, rather than energy-driven. Since Mrk 71-A is a candidate Lyman continuum emitter, this implies that energy-driven superwinds may not be a necessary condition for the escape of ionizing radiation. In addition, the detection of the nebular continuum emission yields an accurate astrometric position for the Mrk 71-A. We also detect four other massive, molecular clouds in this giant star-forming complex.