A MULTI-WAVELENGTH VIEW


This figure shows the SARA broadband optical image (color), combined with the HI intensity map (blue contours), the radio continuum map (white contours), and a ROSAT PSPC X-ray map (yellow contours, from Tschoeke et al. 1999). The contour levels on the X-ray maps are 3-sigma, 4-sigma, 7-sigma, 12-sigma, 19-sigma, etc, above the background, where the noise level is 3 X 10-3 counts arcsec-2.

The difference between the HI and X-ray morphologies of NGC 4410A+B is remarkable. In the X-ray map, a faint elongation extending 2 arcmin (56 kpc) to the east of the NGC 4410 nucleus is apparent. This lies along the stellar bridge connecting NGC 4410A+B with NGC 4410C. In contrast, the extended HI is found mainly along the southeastern stellar tail of NGC 4410A+B, rather than the bridge.

It is not clear at present whether the X-ray emission from the bridge is due to shocked gas in the tidal bridge (as suggested for gas near Fornax A; Mackie and Fabbiano 1998). Alternatively, it may be intragroup gas that is coincidently superposed on the stellar bridge, or background or foreground sources. If the X-ray emitting gas along the bridge is indeed associated with the group, it has an X-ray luminosity of 4 X 1040 erg/s, 10 percent of the total X-ray luminosity of NGC 4410A. Using standard X-ray cooling functions and assuming a face-on flattened cylinder with an axial ratio between 0.1 and 1, the mass of X-ray emitting gas in this extension is 3 - 8 X 108 M(sun), similar to the HI mass in the southeastern tail.