NGC 2276: a remarkable galaxy with a large number of ultraluminous X-ray sources

The starbusting, nearby (D = 32.9 Mpc) spiral (Sc) galaxy NGC 2276 belongs to the sparse group dominated by the elliptical galaxy NGC 2300. NGC 2276 is a remarkable galaxy, as it displays a disturbed morphology at many wavelengths. This is possibly due to gravitational interaction with the central elliptical galaxy of the group. Previous ROSAT and XMM-Newton observations resulted in the detection of extended hot gas emission and of a single very bright (̃10<SUP>41</SUP> erg s<SUP>-1</SUP>) ultraluminous X-ray source (ULX) candidate. Here, we report on a study of the X-ray sources of NGC 2276 based on Chandra data taken in 2004. Chandra was able to resolve 16 sources, 8 of which are ULXs, and to reveal that the previous ULX candidate is actually composed of a few distinct objects. We construct the luminosity function of NGC 2276, which can be interpreted as dominated by high-mass X-ray binaries, and estimate the star formation rate (SFR) to be ̃5-15 M<SUB>☉</SUB> yr<SUP>-1</SUP>, consistent with the values derived from optical and infrared observations. By means of numerical simulations, we show that both ram pressure and viscous transfer effects are necessary to produce the distorted morphology and the high SFR observed in NGC 2276, while tidal interaction have a marginal effect.