A redline starburst: CO(2-1) observations of an Eddington-limited galaxy reveal star formation at its most extreme

TL;DR

This paper presents CO(2-1) observations of a compact, high-luminosity starburst galaxy at z=0.6, revealing star formation near the theoretical maximum regulated by stellar feedback, indicative of a feedback-limited merger-driven growth phase.

Contribution

It provides detailed observations of a galaxy at the extreme end of star formation rates, illustrating a feedback-limited starburst during spheroid formation in a major merger.

Findings

Galaxy forming stars near the Eddington limit for stellar feedback.

High infrared luminosity with low gas fraction and short depletion time.

Evidence of a feedback-limited, merger-driven starburst episode.

Abstract

We report observations of the CO(2-1) emission of SDSSJ1506+54, a compact (r_e~135pc) starburst galaxy at z=0.6. SDSSJ1506+54 appears to be forming stars close to the limit allowed by stellar radiation pressure feedback models: the measured L_IR/L'_CO 1500 is one of the highest measured for any galaxy. With its compact optical morphology but extended low surface brightness envelope, post-starburst spectral features, high infrared luminosity (L_IR>10^12.5 L_Sun), low gas fraction (M_H2/M_stars~15%), and short gas depletion time (tens of Myr), we speculate that this is a feedback- limited central starburst episode at the conclusion of a major merger. Taken as such, SDSSJ1504+54 epitomizes the brief closing stage of a classic model of galaxy growth: we are witnessing a key component of spheroid formation during what we term a 'redline' starburst.