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Another set of surprises come from the presence of "unsuspected" large scale shocks, not seen/foreseen from the optical data. How many are we missing because we are not looking at the right wavelength?

5.1. IC1262

This galaxy, brightest in a small poor group, became interesting because of its high Lx / Lb ratio as seen in the ROSAT All Sky Survey. X-ray emission was later measured to be very extended (>400 kpc), suggesting a large contribution from the group's potential [Trinchieri & Pietsch, 2000]. However, more interesting, the HRI saw an "arc" on leq arcmin scales, that was interpreted as the signature of a shock.

New Chandra data have now shown a quite dramatic view of the system (Fig. 8): a sharp discontinuity east of the central galaxy, with steep drops and a relatively narrow feature along a possible shock front, plus an arc to the NNW, are all indicative of a turmoil in the high energy component, possibly a trace of shocked material caused either by peculiar motions in the system or by a recent merger process. Although a better sampling of the velocity field is needed, neither the optical classification of the galaxy as a cD nor the small velocity dispersion for the group (300 km s-1, [Wegner et al. 1999]) could have suggested anomalous motions of this nature. A proper assessment of the X-ray properties in this and similar systems might be crucial for a more complete understanding of the dynamical and evolutionary properties of small galaxy systems.

Figure 8

Figure 8. The full Chandra field of IC1262 (LEFT). The oval indicates the optical position of the galxy. A turmoil at the center of the more diffuse emission and a sharp discontinuity in surface brightness are evident even in the raw data, in cuts across the narrow features visible.

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