Astronomy and Astrophysics – Astronomy
Scientific paper
Mar 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apjs...97..141e&link_type=abstract
Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 97, no. 1, p. 141-184
Astronomy and Astrophysics
Astronomy
80
Elliptical Galaxies, Infrared Spectra, Interstellar Matter, Luminosity, Radio Emission, Spiral Galaxies, Statistical Analysis, X Ray Spectra, Astronomical Catalogs, Correlation, Heao 2, Infrared Astronomy, Nonlinearity, Radio Astronomy, Tables (Data), X Ray Astronomy
Scientific paper
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 LB and LX, with a power-law slope of 1.8 +/- 0.1, steepening to 2.0 +/- if we do not consider the Local Group dwarf galaxies M32 and NGC 205. Considering only galaxies with log LX less than or equal to 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 LB-LX relationships, the mean values of the distribution functions of both LX and LX/LB 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 LX and the X-ray color C21, 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-LX systems have relatively large contributions from a soft component compared with high-LX 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 L12-L100 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 L100, galaxies with larger LX/LB tend to be stronger nonthermal radio sources, as originally suggested by Kim & Fabbiano (1990). We note that, while LB is most strongly correlated with L6, the total radio luminosity, both LX and LX/LB are more strongly correlated with L6 CO, 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.
Eskridge Paul B.
Fabbiano Giuseppina
Kim Dong-Woo
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