VIMOS-VLT and Spitzer observations of a radio galaxy at z= 2.5*

Villar-Martín, M.; Sánchez, S. F.; De Breuck, C.;Peletier, R.; Vernet, J.; Rettura, A.; Seymour, N.;Humphrey, A.; Stern, D.; di Serego Alighieri, S.;Fosbury, R.. VIMOS-VLT and Spitzer observations of a radio galaxy at z= 2.5*. Monthly Notices of the Royal Astronomical Society: Letters. 2006, Vol. Volume 366, Issue 1, pp. L1-L5, p. -2006.

We present: (i) a kinematic and morphological study of the giant Lyα nebula associated with the radio galaxy MRC 2104-242 (z= 2.49) based on integral field spectroscopic Visible Multiobject Spectrograph (VIMOS) data from the Very Large Telescope (VLT), and (ii) a photometric study of the host (proto?) galaxy based on Spitzer Space Telescope data. The galaxy appears to be embedded in a giant (>~120 kpc) gas reservoir that surrounds it completely. The kinematic properties of the nebula suggest that it is a rotating structure, which would imply a lower limit to the dynamical mass of ~3 × 1011Msolar. An alternate scenario is that the gas is infalling. Such a process would be able to initiate and sustain significant central starburst activity, although it is likely to contribute with less than 10 per cent of the total stellar mass.
The near- to mid-infrared spectral energy distribution of the radio galaxy suggests the existence of a reddened, E(B-V) = 0.4 +/- 0.1, evolved stellar population of age >~1.8 Gyr and mass (5 +/- 2) × 1011Msolar. The implied formation redshift is zf>~ 6. This stellar mass is similar to the stellar masses found for massive early-type galaxies at z~ 2 in deep, near-infrared surveys.