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) Lyα nebulae associated with three radio galaxies at z ~ 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 <~30°. The total Lyα luminosities are in the range (0.3-3.4) × 1044 erg s-1. The Lyα spectral profile shows strong variation through the nebulae, with full width at half-maximum (FWHM) values in the range ~400-1500 kms-1 and velocity shifts Voffset ~ 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 Lyα nebula associated with MRC 1558-003. It can also explain why Lyα is redshifted relative to other emission lines and the FWHM values of the non-resonant HeII 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 Lyα FWHM values, which might be the consequence of a different mechanism.
We have discovered a giant (~85 kpc) Lyα nebula associated with the radio galaxy MRC 0140-257 at z = 2.64. It shows strikingly relaxed kinematics (FWHM < 300 km s-1 and Voffset <~ 120 km s-1), unique among high-z (>~2) radio galaxies.
Based on observations carried out at the European Southern Observatory, Paranal (Chile). Programs 075.B-0212(A) and 073.B-0189(A).