Astronomy and Astrophysics – Astrophysics
Scientific paper
2001-08-06
Astronomy and Astrophysics
Astrophysics
6 pages, 3 included figures, conference "The Central kpc of Starbursts and AGN" La Palma, 2001
Scientific paper
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 L_FIR/L_CO 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 > 10^4 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.
Aalto Samuli
Huttemeister Susanne
Walter Fabian
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