(a) Infrared image of NGC 253 (Engelbracht et al. 1998, ApJ, 505, 639-658). The bar at the lower left represents the length of 1000 parsecs, i.e., 3260 light-years. The green square represents the site of Figures b, c, and d.(b) Hydrogen emission line image of the central region of NGC 253. The color scale represents the difference of hydrogen emission fluxes. The truncated cone represents the position of the galactic wind. Arrows in the cone represent the direction in which the galactic wind is blowing. (c) Nitrogen/hydrogen and (d) sulfur/hydrogen line ratio maps of the central region of NGC 253. The color scale represents the difference of ratios. The green crosses at the centers represent the centers of NGC 253, while white bars at the lower right represent the length of 100 parsecs, i.e., 326 light-years.

(PhysOrg.com) — A research group at Kyoto University has discovered that shocks are the primary energy sources that excite the galactic wind region of starburst galaxy NGC 253. Their images of the center of this galaxy, bright with intense star formation, have generated findings that substantially increase our meager knowledge of the physical properties of galactic winds and move us closer to understanding galaxy evolution.

Galactic winds (galaxy-scale outflows) are familiar phenomena in both nearby and faraway galaxies. Stellar winds, supernovae (explosions of stars) or (AGNs) can feed their energy. Astronomers believe that they have a significant impact on galaxy evolution. Some suggest that galactic winds may suppress star formation by removing interstellar gas from host galaxies. Nevertheless, investigations of their physical properties have been limited and insufficient, given their likely significance in .

The challenge of observing galactic winds

Because galactic winds appear as faint, diffuse objects with extremely complex structures, they have been difficult to observe. Since the mid-1990s, the advent of large ground-based telescopes with innovative instrumentation has opened the door for more precise observations of these important but elusive targets. It was during the 28 August 2002 testing of the Kyoto tridimensional spectrograph II (Kyoto 3DII), mounted on the Subaru Telescope in Hawaii, that its Kyoto development team observed the central region of NGC 253. The combination of Subaru's large, 8.2m aperture with the sensitivity of the spectrograph's Fabry-Perot interferometer observation mode to faint emissions produced a complete image of the galactic wind in NGC 253 in one exposure. Although partial spectroscopic observations of its wind have been made in the past, this is the first time that a spectroscopic instrument has captured an image of the entire galactic wind.

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