Giant Biconical Dust Filaments in the Starburst Galaxy NGC 1808

Abstract

We present the results from an analysis of multiwavelength archival data on the multiphase outflow in the starburst galaxy NGC 1808. We report the detection at 70 and 100 μ m of dust filaments that extend up to ∼13 kpc from the galactic midplane and trace an edge-brightened biconical structure along the minor axis of the galaxy. The inner filaments are roughly cospatial with previously identified optical dust filaments, extraplanar polycyclic aromatic hydrocarbon emission, and neutral and ionized gaseous outflows. The 70/160 μ m flux ratio, a proxy for the dust temperature, is elevated along the edges of the cones, indicating that the dusty medium has been driven out of the central regions of these cones and is possibly shock-heated by a large-scale outflow. We establish lower limits on the extraplanar dust mass and mean height above the stellar disk of $\mathrm{log}({M}_{d}/{M}_{\odot })\,=\,6.48$ and ∣ z ∣ ∼ 5 kpc. The energy requirement of (5.1–9.6) × 10 ^56 erg needed to lift the dusty material, assuming a Milky Way–like dust-to-gas ratio, can be supplied by the current starburst, with a measured star formation rate of 3.5–5.4 M _⊙ yr ^−1 over a timescale of (4–26) ξ ^−1 Myr, where ξ is the efficiency of energy transfer. We conclude that a starburst-driven outflow is the most likely mechanism by which the dust features were formed.

Keywords

• Galactic winds
• Stellar feedback
• Starburst galaxies
• Circumgalactic medium
• Dust physics
• Shocks