VIMOS-VLT spectroscopy of the giant Lyα nebulae associated with three z∼ 2.5 radio galaxies

The morphological and spectroscopic properties of the giant (> 60 kpc) Ly alpha nebulae associated with three radio galaxies at z similar to 2.5 (MRC 1558-003, 2025-218 and 0140-257) have been investigated using integral field spectroscopic data obtained with the Visible Multi-Object Spectrograph (VIMOS) on VLT. The morphologies are varied. The nebula of one source has a centrally peaked, rounded appearance. In the other two objects, it consists of two spatial components. The three nebulae are aligned with the radio axis within less than or similar to 30 degrees. The total Ly alpha luminosities are in the range (0.3-3.4) x 10(44) erg s(-1). The Ly alpha spectral profile shows strong variation through the nebulae, with full width at half-maximum (FWHM) values in the range similar to 400-1500 km s(-1) and velocity shifts V-offset similar to 120-600 km s(-1). We present an infall model that can successfully explain the morphology, size, surface brightness distribution and the velocity field of the Ly alpha nebula associated with MRC 1558-003. It can also explain why Ly alpha is redshifted relative to other emission lines and the FWHM values of the non-resonant He II line. This adds further support to our previous conclusion that the quiescent giant nebulae associated with this and other high-redshift powerful radio galaxies are in infall. A problem for this model is the difficulty to reproduce the large Ly alpha FWHM values, which might be the consequence of a different mechanism. We have discovered a giant (similar to 85 kpc) Ly alpha nebula associated with the radio galaxy MRC 0140-257 at z = 2.64. It shows strikingly relaxed kinematics (FWHM < 300 km s(-1) and V-offset less than or similar to 120 km s(-1)), unique among high-z (greater than or similar to 2) radio galaxies.