%APasha, Imad%ALokhorst, Deborah%Avan Dokkum, Pieter%AChen, Seery%AAbraham, Roberto%AGreco, Johnny%ADanieli, Shany%AMiller, Tim%ALippitt, Erin%APolzin, Ava%AShen, Zili%AKeim, Michael%ALiu, Qing%AMerritt, Allison%AZhang, Jielai%BJournal Name: The Astrophysical Journal Letters; Journal Volume: 923; Journal Issue: 2 %D2021%I %JJournal Name: The Astrophysical Journal Letters; Journal Volume: 923; Journal Issue: 2 %K %MOSTI ID: 10320261 %PMedium: X %TA Nascent Tidal Dwarf Galaxy Forming within the Northern H i Streamer of M82 %XAbstract We identify a ∼600 pc wide region of active star formation located within a tidal streamer of M82 via H α emission ( F H α ∼ 6.5 × 10 −14 erg s −1 cm −2 ), using a pathfinder instrument based on the Dragonfly Telephoto Array. The object is kinematically decoupled from the disk of M82 as confirmed via Keck/LRIS spectroscopy and is spatially and kinematically coincident with an overdensity of H i and molecular hydrogen within the “northern H i streamer” induced by the passage of M81 several hundred Myr ago. From H i data, we estimate that ∼5 × 10 7 M ⊙ of gas is present in the specific overdensity coincident with the H α source. The object’s derived metallicity (12+ log ( O / H ) ≃ 8.6 ), position within a gas-rich tidal feature, and morphology (600 pc diameter with multiple star-forming clumps), indicate that it is likely a tidal dwarf galaxy in the earliest stages of formation. %0Journal Article