Correlations among Multi-Wavelength Luminosities of Star-Forming Galaxies

Abstract

It has been known for two decades that a tight correlation exists between far-infrared (FIR) and radio (1.4 and 4.8 GHz) global fluxes/luminosities from galaxies, which may be explained in terms of massive star formation activities in these galaxies. For this very reason, a correlation might also exist between X-ray and FIR/radio global luminosities of galaxies. We analyze data from {\it ROSAT} All-Sky Survey and {\it IRAS} to show that such correlation does indeed exist between FIR (42.5$-122.5\mu$m) and soft X-ray (0.1$-$2.4keV) luminosities in active star-forming galaxies (ASFGs).In order to establish a physical connection between the $L_{\rmX}-L_{\rm FIR}$ correlation and global star formation rate (SFR) in galaxies, we empirically derive both $L_{\rm X}-L_{\rm B}$ and $L_{\rm FIR}-L_{\rm B}$ relations. Futhermore, we propose a relation between soft X-ray luminosity and SFR in star-forming galaxies. To further understand the $L_{\rm X}-L_{\rm FIR}$ relation, we construct an empirical model in which both FIR and X-ray emissions consist of two components with one being closely associated with star formation and the other not.