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[116.05] HST/NICMOS Imaging of the Emission-Line Nebulae and Line-Free Continuum in the \boldmath z=2.3 Radio Galaxy 4C 40.36

E. Egami (Caltech), L. Armus (SIRTF), G. Neugebauer, B.T. Soifer, T.W. Murphy, Jr. (Caltech), A.S. Evans (SUNY)

Using NICMOS on HST, we have imaged the emission-line nebulae and line-free continuum in 4C 40.36, a ultra-steep spectrum FR II radio galaxy at z=2.269. The emission-line nebulae seen in H\alpha+[N~II] and [O~III] show very clumpy structures spreading almost linearly over 16 kpc (q₀=0.5; H₀=50 km s^-1 Mpc^-1). However, this linear structure is clearly misaligned from the radio axis, which may indicate that it is not the expanding jet that is ionizing the gas. The near-IR (i.e., restframe optical) line-free continuum, on the other hand, is extremely compact and symmetric. It has an unresolved core (PSF FWHM = 0\farcs2 = 1.6 kpc) and an almost circularly symmetric halo extending out to at least a radius of ~ 4 kpc. A comparison with the optical (i.e., restframe UV) data shows that the intrinsic SED of the continuum is extremely flat (f_\nu \propto \nu^-0.5) from the restframe UV to optical, suggesting that the continuum source is either a young bursting stellar population or scattered AGN light.