THE DISPLACED DUSTY INTERSTELLAR MEDIUM OF NGC 3077: TIDAL STRIPPING IN THE M 81 TRIPLET

We present the detection of extended (∼30 kpc2) dust emission in the tidal H i arm near NGC 3077 (member of the M 81 triplet) using SPIRE on board Herschel. Dust emission in the tidal arm is typically detected where the H i column densities are >1021 cm−2. The SPIRE band ratios show that the dust in the tidal arm is significantly colder (∼13 K) than in NGC 3077 itself (∼31 K), consistent with the lower radiation field in the tidal arm. The total dust mass in the tidal arm is ∼1.8 × 106 M☉ (assuming β = 2), i.e., substantially larger than the dust mass associated with NGC 3077 (∼2 × 105 M☉). Where dust is detected, the dust-to-gas ratio is (6 ± 3) × 10−3, consistent within the uncertainties with what is found in NGC 3077 and nearby spiral galaxies with Galactic metallicities. The faint H ii regions in the tidal arm cannot be responsible for the detected enriched material and are not the main source of the dust heating in the tidal arm. We conclude that the interstellar medium (atomic H i, molecules, and dust) in this tidal feature was pre-enriched and stripped off NGC 3077 during its recent interaction (∼3 × 108 yr ago) with M 82 and M 81. This implies that interaction can efficiently remove heavy elements and enriched material (dust and molecular gas) from galaxies. As interactions were more frequent at large look-back times, it is conceivable that they could substantially contribute (along with galactic outflows) to the enrichment of the intergalactic medium.