Molecular Superbubbles and Outflows from the Starburst Galaxy NGC 2146

Abstract

We present results from a deep (1σ = 5.7 mJy beam −1 per 20.8 km s −1 velocity channel) 12 CO(1-0) interferometric observation of the central 60 ′′ region of the nearby edge-on starburst galaxy NGC 2146 observed with the Nobeyama Millimeter Array (NMA). Two diffuse expanding molecular superbubbles and one molecular outflow are successfully detected. One molecular superbubble, with a size of ∼ 1 kpc and an expansion velocity of ∼ 50 km s −1 , is located below the galactic disk; a second molecular superbubble, this time with a size of ∼ 700 pc and an expansion velocity of ∼ 35 km s −1 , is also seen in the position-velocity diagram; the molecular outflow is located above the galactic disk with an extent ∼ 2 kpc, expanding with a velocity of up to ∼ 200 km s −1 . The molecular outflow has an arc-like structure, and is located at the front edge of the soft X-ray outflow. In addition, the kinetic energy (∼ 3×10 55 erg) and the pressure (∼ 1 × 10 −12±1 dyne cm −2 ) of the molecular outflow is comparable to or smaller than that of the hot thermal plasma, suggesting that the hot plasma pushes the molecular gas out from the galactic disk. Inside the ∼ 1 kpc size molecular superbubble, diffuse soft X-ray emission seems to exist. But since the superbubble 1 lies behind the inclined galactic disk, it is largely absorbed by the molecular gas.

Evidence for a chemically differentiated outflow in Mrk 231

“…Many galactic winds and outflows drive out large amounts of molecular gas (see e.g. Nakai et al 1987;Walter et al 2002;Sakamoto et al 2006;Tsai et al 2009;Alatalo et al 2011;Sturm et al 2011;Aalto et al 2012b;Bolatto et al 2013) and the ultimate fate of the expelled cold gas is not understood. It is also not clear if the molecular gas is formed in the outflow itself, or if it is carried out from the disc in molecular form.…”

A Review of Recent Observations of Galactic Winds Driven by Star Formation

“…Recent interferometric measurements of CO transitions have uncovered outflowing cold molecular gas in approximately 11 nearby LIRGs and ULIRGs whose energy output is dominated by star formation [72][73][74][75][76][77][78][79]. Molecular outflows in four very nearby star-forming galaxies with lower SFR have also been studied in detail: NGC 3628, M82, NGC 253 ( Figure 3), and NGC 1808 [80][81][82][83].…”

Astrochemistry and star formation in nearby galaxies: from galaxy disks to hot nuclei

“…Many galactic winds and outflows carry large amounts of molecular gas and dust with them and there is a growing list of examples of molecular gas in outflows in nearby galaxies (e.g. Nakai et al, 1987;García-Burillo et al, 2000, 2001Walter et al, 2002;Sakamoto et al, 2006;Tsai et al, 2009;Fischer et al, 2010;Feruglio et al, 2010;Alatalo et al, 2011;Sturm et al, 2011;Aalto et al, 2012a,b;Bolatto et al, 2013;Sakamoto et al, 2014;Veilleux et al, 2013;Cicone et al, 2014;García-Burillo et al, 2014;Matsushita et al, 2015;Aalto et al, 2015c). Studying the physical and chemical conditions of the outflowing molecular gas will help us understand the driving mechanism, origin of the gas and its fate in the wind.…”