New ULX in the collisional ring galaxy NGC 922
Abstract
We present a new Chandra observation of the nearby collisional ring galaxy NGC 922. NGC 922 is undergoing a violent burst of star formation as density waves are driven through the disk as a result of the collision. It is similar to the famous Cartwheel galaxy, except that the metallicity is somewhat higher and star formation rate lower. Our primary science goal is to determine whether a low metallicty environment is required to form the most luminous X-ray sources (L_x>10^{40} ergs s^{-1}). We find a total of 14 bright X-ray sources, 7 of which are ULX (L_x>10^{39} ergs s^{-1}). One source has L_x∼ 10^{40} ergs s^{-1}. The X-ray sources are associated with the H-alpha ring. However, they are NOT associated with the brightest H-alpha patches, suggesting that the ULX phase starts >1×10^{7} years after the starburst. Like the Cartwheel, the X-ray luminosity function of NGC 922 has a slope close to that of the ``cannonical'' HMXB slope of Gilfanov et al 2004. We conclude that NGC 922 is forming ULX as efficiently as the Cartwheel (after allowing for the difference in the star formation rate). We do not see a strong metallicity effect.
- Publication:
-
Chandra's First Decade of Discovery
- Pub Date:
- September 2009
- Bibcode:
- 2009cfdd.confE.182P
- Keywords:
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- Compact Objects