A comprehensive X-ray and multiwavelength study of the colliding galaxy pair NGC 2207/IC 2163

Abstract

We present a comprehensive study of the total X-ray emission from the colliding galaxy pair NGC 2207/IC 2163, based on Chandra, Spitzer, and GALEX data. We detect 28 ultraluminous X-ray sources (ULXs), 7 of which were not detected previously because of X-ray variability. Twelve sources show significant long-term variability, with no correlated spectral changes. Seven sources are transient candidates. One ULX coincides with an extremely blue star cluster (B - V = -0.7). We confirm that the global relation between the number and luminosity of ULXs and the integrated star-formation rate (SFR) of the host galaxy also holds on local scales.We investigate the effects of dust extinction and age on the X-ray binary (XRB) population on subgalactic scales. The distributions of NX and LX are peaked at LIR/LNUV ∼ 1, which may be associated with an age of ∼ 10 Myr for the underlying stellar population. We find that approximately one-third of the XRBs are located in close proximity to young star complexes. The luminosity function of the XRBs is consistent with that typical for high-mass XRBs and appears unaffected by variability.We disentangle and compare the X-ray diffuse spectrum with that of the bright XRBs. The hot interstellar medium dominates the diffuse X-ray emission at E ≲ 1 keV and has a temperature kT = 0.28-0.04+0.05 keVand intrinsic 0.5-2 keV luminosity of 7.9 × 1040 erg s-1, a factor of ∼2.3 higher than the average thermal luminosity produced per unit SFR in local star-forming galaxies. The total X-ray output of NGC 2207/IC 2163 is 1.5 × 1041 erg s-1, and the corresponding total integrated SFR is 23.7M⊙ yr-1.