Giant H$\alpha$ nebula surrounding the starburst merger NGC 6240

Abstract

We revealed the detailed structure of a vastly extended H$\alpha$-emitting nebula ("H$\alpha$ nebula") surrounding the starburst/merging galaxy NGC 6240 by deep narrow-band imaging observations with the Subaru Suprime-Cam. The extent of the nebula is $\sim$90 kpc in diameter and the total H$\alpha$ luminosity amounts to $\approx 1.6\times 10^{42}$ erg s${}^{-1}$. The volume filling factor and the mass of the warm ionized gas are $\sim$10${}^{-4}$--10${}^{-5}$ and $\sim$$5\times 10^8$ $M_{\odot }$, respectively. The nebula has a complicated structure, which includes numerous filaments, loops, bubbles, and knots. We found that there is a tight spatial correlation between the H$\alpha$ nebula and the extended soft X-ray-emitting gas, both in large and small scales. The overall morphology of the nebula is dominated by filamentary structures radially extending from the center of the galaxy. A large-scale bi-polar bubble extends along the minor axis of the main stellar disk. The morphology strongly suggests that the nebula was formed by intense outflows - superwinds - driven by starbursts. We also found three bright knots embedded in a looped filament of ionized gas that show head-tail morphologies in both emission-line and continuum, suggesting close interactions between the outflows and star forming regions. Based on the morphology and surface brightness distribution of the H$\alpha$ nebula, we propose the scenario that three major episodes of starburst/superwind activities which were initiated $\sim$10${}^2$ Myr ago formed the extended ionized gas nebula of NGC 6240.

17 pages, 12 figures. Accepted by ApJ

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• The Anisotropic Circumgalactic Medium of Massive Early-Type Galaxies
• The TELPERION Survey for Distant [O III] Clouds around Luminous and Hibernating AGN
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• An Empirical Determination of the Dependence of the Circumgalactic Mass Cooling Rate and Feedback Mass Loading Factor on Galactic Stellar Mass
• Observing the Effects of Galaxy Interactions on the Circumgalactic Medium
• Dissecting the Extended X-ray Emission in the Merging Pair NGC 6240
• Outflowing shocked gas dominates the NIR H${}_2$ emission from the dual AGN NGC6240
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