The Discovery of a Molecular Complex in the Tidal Arms near NGC 3077

We present the discovery of a giant molecular complex ( r ≈ 350 pc, M vir ≈ 10 7 M ☉ ) in the tidal arms southeast of NGC 3077, a member of the M81 triplet. The complex is clearly detected in the 12 CO ( J = 1 → 0) transition at five independent positions. The position relative to NGC 3077, the systemic velocity ( v hel ≈ 14 km s -1 ), and the cloud-averaged line width (Δ v ≈ 15 km s -1 ) indicate that the object is not related to Galactic cirrus, but is extragalactic. The tidal H I arm in which the molecular complex is located has a total H I mass of M vir ≈ 3 × 10 8 M ☉ . This tidal material was presumably stripped off the outer parts of NGC 3077 during the closest encounter with M81, about 3 × 10 8 yr ago. After the complex detected along a torn-out spiral arm of M81 by Brouillet et al., it is the second of its kind reported so far. Based on published optical observations, we have no evidence for ongoing star formation in the newly detected molecular complex. Since the system has all the ingredients to form stars in the future, we speculate that it might eventually resemble the young dwarf galaxies in the M81 group.