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For refcode 1995ApJS...97..141E:
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1995ApJS...97..141E A MULTIPARAMETRIC ANALYSIS OF THE EINSTEIN SAMPLE OF EARLY-TYPE GALAXIES. I. LUMINOSITY AND ISM PARAMETERS PAUL B. ESKRIDGE AND GIUSEPPINA FABBIANO Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138; paul@hera.astr.ua.edu, pepi@cfa.harvard.edu AND DONG-WOO KIM Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138; and Department of Astronomy and Space Science, Chungnam National University, Taejon, 305-764, South Korea; kim@cfa.harvard.edu Received 1994 May 16; accepted 1994 July 28 ABSTRACT We have conducted bivariate and multivariate statistical analysis of data measuring the luminosity and interstellar medium of the Einstein sample of early-type galaxies (presented by Fabbiano, Kim, & Trinchieri 1992). We find a strong nonlinear correlation between L_B_ and L_X_, with a power-law slope of 1.8 +/- 0.1, steepening to 2.0 +/- 0.2 if we do not consider the Local Group dwarf galaxies M32 and NGC 205. Considering only galaxies with log L_X_ <+ 40.5, we instead find a slope of 1.0 +/- 0.2 (with or without the Local Group dwarfs). Although E and S0 galaxies have consistent slopes for their L_B_-L_X_ relationships, the mean values of the distribution functions of both L_X_ and L_X_/L_B_ for the S0 galaxies are lower than those for the E galaxies at the 2.8 {sigma} and 3.5 {sigma} levels, respectively. We find clear evidence for a correlation between L_X_ and the X-ray color C_21_, defined by Kim, Fabbiano, & Trinchieri (1992b), which indicates that X-ray luminosity is correlated with the spectral shape below 1 keV in the sense that low-L_X_ systems have relatively large contributions from a soft component compared with high-L_X_ systems. We find evidence from our analysis of the 12 micron IRAS data for our sample that our S0 sample has excess 12 micron emission compared with the E sample, scaled by their optical luminosities. This may be due to emission from dust heated in star-forming regions in S0 disks. This interpretation is reinforced by the existence of a strong L_12_-L_100_ correlation for our S0 sample that is not found for the E galaxies, and by an analysis of optical-IR colors. We find steep slopes for power-law relationships between radio luminosity and optical, X-ray, and far- IR (FIR) properties. This last point argues that the presence of an FIR-emitting interstellar medium (ISM) in early-type galaxies is coupled to their ability to generate nonthermal radio continuum, as previously argued by, e.g., Walsh et al. (1989). We also find that, for a given L_100_, galaxies with larger L_X_/L_B_ tend to be stronger nonthermal radio sources, as originally suggested by Kim & Fabbiano (1990). We note that, while L_B_ is most strongly correlated with L_6_, the total radio luminosity, both L_X_ and L_X_/L_B_ are more strongly correlated with L_6co_, the core radio luminosity. These points support the argument (proposed by Fabbiano, Gioia, & Trinchieri 1989) that radio cores in early-type galaxies are fueled by the hot ISM. Subject headings: galaxies: elliptical and lenticular, cD - galaxies: general - galaxies: ISM - X-rays: galaxies
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