New multi-band observations of the famous compact group of galaxies Stephan ’ s Quintet ( SQ ) are presented and analyzed .
These include far infrared ( FIR ) images at 60 \mu m and 100 \mu m ( ISOPHOT C-100 camera ) , radio continuum images at 1.4 GHz ( VLA B-array ) and 4.86 GHz ( VLA C-array ) , and long-slit optical spectrographs ( Palomar 200 " telescope ) .
With these new data , we aim to learn more about the X-ray/radio ridge in the middle of the intragroup medium ( IGM ) and the IGM starburst SQ-A , both are likely to be caused by the high speed collision ( \sim 900 
km s ^ { -1 } ) between the intruder galaxy NGC 7318b ( v = 5700 km s ^ { -1 } ) and the IGM ( v = 6600 km s ^ { -1 } ) .
We found that the radio ridge has a steep nonthermal spectral index ( \alpha = 0.93 \pm 0.13 ) and an extremely low FIR-to-radio ratio index ( q < 0.59 ) .
Its IR emission can be explained in terms of collisional heating of dust grains by shocked gas .
The minimum-energy magnetic field strength is H _ { min } \approx 10 \mu G. The long-slit spectra of sources in the ridge have typical emission line ratios of shock-excited gas .
The very broad line widths ( \geq 1000 km s ^ { -1 } ) , and the fact that in some cases more than two velocity systems were detected along the same line of sight , provide further evidence for an ongoing collision along the ridge .
The IGM starburst SQ-A has a radio spectral index \alpha = 0.8 \pm 0.3 
and a FIR-to-radio ratio index q = 2.0 \pm 0.4 , consistent with those of star forming regions .
The optical spectra of two sources in this region , M1 ( v = 6600 km s ^ { -1 } ) and M2 ( v = 6000 km s ^ { -1 } ) , have typical line ratios of HII regions .
Both M1 and M2 have metallicity slightly higher than the solar value .
The star formation rate ( SFR ) estimated from the extinction-corrected H _ { \alpha } luminosity of SQ-A is 1.45 M _ { \odot } yr ^ { -1 } , of which 1.25 M _ { \odot } yr ^ { -1 } is due to the v = 6600 km s ^ { -1 } component and 0.20 M _ { \odot } yr ^ { -1 } to the v = 6000 km s ^ { -1 } component .