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Session 77 - Structures of Galaxies.
Display session, Friday, January 09
We present the analysis of a sample of 234 spiral and irregular galaxies - strong AGN excluded - observed in X-rays with the Einstein Observatory. We have complemented X-ray and optical data with H-band magnitudes, and near-, far-infrared, and radio continuum (6cm) flux densities from literature searches. Morphological dependencies were explored by looking separately at S0/a-Sab, Sb- Sbc, and Sc-Irr galaxies. We applied bivariate and multivariate survival analysis techniques that make full use of all the information available in both detections and limits. We find that most pairs of luminosities are correlated when considered individually, and this is not due to a distance bias. Different correlations follow different power-law relations. Both the significances of some correlations and their power-law relations are morphology dependent and can be linked to the effect of the bulge component and in some cases possibly to nuclear emission. We find two fundamentally strong correlations, regardless of galaxy morphology: L_B - L_H and L_12 - L_FIR. The former links stellar emission processes, and points to a basic connection between the initial mass function (IMF) of low-mass and intermediate-to-high-mass stars. The latter may be related to the heating of small and larger size dust grains by the same UV photon field. Other highly significant `fundamental' correlations exist, but are morphology-dependent. In particular, in the late sample (Sb-Sbc) there is an indication of an overall connection of X-ray, mid- and far-IR, and radio-continuum emission, which could be related to the presence of star-forming activity in these galaxies.
Program listing for Friday