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NGC 253 is a spectacular, nearly edge-on (inclination of approximately 70° to our line of sight), starburst spiral. It is 3 Mpc distant in the South Polar Group or Sculptor Group. NGC 253 is rapidly forming stars, at rates of one to two orders of magnitude greater than more normal spirals. It is ~20% as massive as the Galaxy or NGC 224/M 31.
Itoh et al. (2002) detected TeV gamma-ray emission greater than 0.5 TeV with the CANGAROO-II 10 m imaging atmospheric Cerenkov telescope.
Pietsch (1994) and Vogler and Pietsch (1999) show ROSAT PSPC images. The (0.1–2.4 keV) X-ray image shows discrete sources (probably low- and high-mass X-ray binary systems), with a high concentration near the nucleus, as well as faint diffuse emission. The soft (0.1–0.4 keV) image shows spectacular diffuse emission extending above the plane of the galaxy. This emission is 105–6 K gas being energized and ejected from the plane by SN explosions. Weaver et al. (2002) present CXO ACIS data and detect a heavily absorbed source (>1039 ergs s-1) of hard X-rays embedded within the nuclear starburst region.
OVRO CO observations (Canzian, Mundy and Scoville 1988) detect a large amount of molecular gas in the form of a central bar. The mass is ~5 × 108 M⊙ and displays rigid body rotation suggesting the existence of a large mass in the center of the galaxy. High-resolution VLA radio continuum images (Ulvestad and Antonucci 1997) show numerous compact sources in the inner 200 pc.