ON THE FR-I FR-II DICHOTOMY IN POWERFUL RADIO-SOURCES - ANALYSIS OF THEIR EMISSION-LINE AND RADIO LUMINOSITIES

We know from previous work that there are substantial differences betw een powerful FR I and FR II radio galaxies. In this paper we look at t he correlations of line luminosity, radio luminosity, core radio power , and host galaxy optical magnitude independently for FR I and FR II r adio galaxies and compare these correlations with those for an optical ly selected control sample of early-type galaxies. In this, Paper I in a two-paper series, we list the principal results; in Paper II we dis cuss the implications of these results for our understanding of the FR I-FR II dichotomy and the central engines of powerful radio galaxies. Our principal results are the following. Correlating core power to to tal power we find: (1) The difference between the radio core powers of FR I and FR II galaxies is less than the difference between the exten ded radio powers: the median total radio powers of FR II galaxies in o ur sample are about 40 times greater than those of FR I galaxies, whil e the median radio core powers of FR II galaxies in our sample are onl y about 4 times greater than those of FR I galaxies. (2) In agreement with previous work, we find a decrease (with slope -0.38 +/- 0.05) in the ratio of core to lobe radio power, the R-parameter, with increasin g total radio power. However, there is a significant scatter (2 orders of magnitude) in the R-parameter. (3) At a fixed total radio power, F R I and FR II galaxies have the same ratio of core to lobe power and a comparable scatter. We investigate the possibility of systematic effe cts skewing these results but find no evidence for this: (1) The R-par ameter is not affected by redshift selection effects. (2) Orientation and beaming effects are either dominated by the large intrinsic scatte r in the R-parameter, or they themselves produce that scatter. Since t he scatter is the same for FR I and FR II sources, beaming effects mus t be equally important or unimportant in both FR types. We analyze the three-way correlation between redshift, radio power, and emission-lin e luminosity and find that the correlation of radio power with redshif t is stronger than that of emission-line luminosity with redshift. In fact, for the FR I galaxies there is virtually no correlation between line luminosity and redshift. When correlating the total radio power t o the emission-line luminosity for our full sample of radio-loud galax ies, we find that these two parameters are strongly correlated over 8 orders of magnitude in emission-line luminosity and 10 orders of magni tude in total radio power. When we look independently at the correlati ons for FR I and FR II radio galaxies, we find: (1) Each FR type has i ts own independent correlation of radio power and emission-line lumino sity. (2) The functional relationships between emission-line luminosit y (L(line)) ,and radio power (P-408 (MHz)) are different; L(line) = (0 .75 +/- 0.08) x P-408 (MHz) + (14.8 +/- 2.3) for FR II galaxies and L( line) = (0.28 +/- 0.07) x P-408 (MHz) + (26.3 +/- 1.8) for FR I galaxi es. (3) The FR I and FR II radio sources are offset with respect to on e another in the radio-line luminosity plane, which can be described i n two fashions: for the same total radio power as the FR I galaxies, t he FR II galaxies produce consistently about 5-30 times as much emissi on-line luminosity; or, for the same amount of emission-line activity as the FR II galaxies, the FR I galaxies produce about 10-100 times as much total radio power. (4) For FR I sources and optically selected s ources, we find a correlation of line luminosity with host galaxy opti cal magnitude (there is none for FR II galaxies). Removing the depende nce of line luminosity on host galaxy optical magnitude, we find a 2 s igma dependence of line luminosity on radio luminosity for FR I source s. Correlating the core radio powers to the emission-line luminosities , we find: (1) Each FR type has its own correlation between the radio core power and the emission-line luminosity. Both correlations are as good as those between total power and emission-line luminosity. (2) Th e functional relationships for FR I and FR II sources are again differ ent; L(line) (0.62 +/- 0.10) x P-core + (19.9 +/- 2.3) for FR II galax ies and L(line) = (0.30 +/- 0.12) x P-core + (26.3 +/- 2.8) for FR I g alaxies. (3) The two FR types separate out even more clearly in the co re radio power-emission-line luminosity plane than in the total radio power-line luminosity plane. For the same radio core power as the FR I galaxies, the FR II galaxies produce consistently about 10-50 times a s much emission-line luminosity; or, for the same amount of emission-l ine activity as the FR II galaxies, the FR I galaxies produce about 20 0-300 times as much radio core power. The most important result is tha t FR I and FR II radio sources display strong differences in their cor relations of line luminosity, ratio total and core power, and host gal axy optical magnitude. These differences may reflect fundamental diffe rences in the properties of the central engines in these two types of radio galaxies. A detailed discussion of the implications is deferred to Paper II.