Molecular Gas and Star Formation in the NGC 3077 Tidal Arm

. We report the discovery of extended star formation in the prominent tidal arms near NGC 3077 (member of the M 81 triplet). 36 faint compact star forming regions were identified, covering an area of 4 x 6 kpc 2. HII regions are only found near the southern rim of the tidal HI arm where the HI column density reaches values above 1 x 10 21 em -2. This threshold is very similar to what is found in 'normal' galactic environments. We derive a total star formation rate of 2.6 x 10- 3 M 8 yr- 1 in the tidal feature. We also present the first high-resolution observations of molecular gas in this region. The molecular gas emission can be separated into at least 5 distinct complexes most of which do not coincide with sites of star formation. The reservoir of neutral and molecular gas in the tidal arm is huge (rv 5 X 10 8 M 8 ); star formation may continue at the given rate for a Hubble time. We conclude that wide-spread low-level star formation may be a common phenomenon in tidal HI tails, however it will be difficult to detect in interacting systems that are further away.

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