Deep SAURON Spectral-Imaging of the diffuse Lyman-alpha halo LAB1 in SSA22

We have used the SAURON panoramic integral field spectrograph to study the structure of the Ly-α emission-line halo, LAB1, surrounding the sub-millimeter galaxy SMM J221726+0013. This emission-line halo was discovered during a narrow-band imaging survey of the z = 3.1 large-scale structure in the SSA22 region. Our observations trace the emission halo out to almost 100 kpc from the sub-millimeter source and identify two distinct Ly-α “mini-haloes” around the nearby Lyman-break galaxies. The main emission region has a broad line profile, with variations in the line profile seeming chaotic and lacking evidence for a coherent velocity structure. The data also suggests that Ly-α emission is suppressed around the sub-mm source. Interpretation of the line structure needs care because Ly-α may be resonantly scattered, leading to complex radiative transfer effects, and we suggest that the suppression in this region arises because of such effects. We compare the structure of the central emission-line halo with local counter-parts, and find that the emission line halo around NGC 1275 in the Perseus cluster may be a good local analogue, although the high redshift halo is factor of ∼100 more luminous and appears to have higher velocity broadening. Around the Lyman-break galaxy C15, the emission line is narrower, and a clear shear in the emission wavelength is seen. A plausible explanation for the line profile is that the emission gas is expelled from C15 in a bipolar outflow, similar to that seen in M82.