Gas properties in the Medusa minor merger - comparing with ULIRGs
Abstract
High resolution observations of CO and 13CO 1--0 in the Medusa (NGC4194) minor merger show the CO/13CO 1--0 intensity ratio (R) increasing from normal values (5-10) in the outer parts of the galaxy to high (>20) values in the central, extended starburst region. Ratios >20 are otherwise typical of more luminous mergers. The Medusa LFIR/LCO ratio rivals that of ultraluminous galaxies (ULIRGs), despite the comparatively modest luminosity, indicating an exceptionally high star formation efficiency (SFE). We present models of the high pressure ISM in a ULIRG and the relatively low pressure ISM of the Medusa. We discuss how these models may explain large R in both types of distributions. Since the HCN emission is faint towards the Medusa, we suggest that the SFE is not primarily controlled by the mass fraction of dense (n > 104 cm-3) gas, but is probably strongly dependent on dynamics. The bright HCN emission towards ULIRGs is not necessarily evidence that the IR emission there is always powered by starbursts.
Turn this paper into a full lesson
ArcXiv compiles a staged curriculum from this paper: 8-12 lessons across beginner → advanced, synthesised section guides, visuals, flashcards, a quiz, exercises, and on-demand deep dives per section. Grounded in the abstract, never invented.