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The stellar populations of nearby radiogalaxies I. Aretxaga 1 , E. Terlevich 1 , R.J. Terlevich 2;1 , G. Cotter 3 , and A.I. D az 4
 

Summary: The stellar populations of nearby radiogalaxies
I. Aretxaga 1 , E. Terlevich 1 , R.J. Terlevich 2;1 , G. Cotter 3 , and A.I. Daz 4
1 INAOE, Aptdo. Postal 51 y 216, Puebla, Pue., Mexico
2 IoA, Univ. of Cambridge, UK
3 Cavendish Lab., Univ. of Cambridge, UK.
4 Dpto. Fsica Teorica, UAM, Spain.
Abstract. We present results on a sample of 7 nearby luminous radiogalaxies (z <
0:08, P 178MHz >  10 25 W Hz 1 Sr 1 ), which mostly correspond to the FR II class.
In two cases, Hydra A and 3C 285, the Balmer and 4000 break indices constrain
the spectral types and luminosity classes of the stars involved, revealing that the blue
spectra are dominated by blue supergiant and/or giant stars. The ages derived for the
last burst of star formation in Hydra A are between 7 and 40 Myr, and in 3C 285 about
10 Myr. The rest of the narrow-line radiogalaxies (four) have 4000 break and metallic
indices consistent with those of elliptical galaxies. The only broad-line radiogalaxy in
our sample, 3C 382, has a strong featureless blue continuum and broad emission lines
that dilute the underlying blue stellar spectra.
1 Introduction
In recent years direct evidence that star formation plays an important role in Ac-
tive Galactic Nuclei (AGN) has been gathered [9][3][1][4] through the detection
of stellar atmospheric features that indicate that most of the UV-NIR light com-

  

Source: Aretxaga, Itziar - Instituto Nacional de Astrofísica Óptica y Electrónica

 

Collections: Physics