http://arxiv.org/abs/2001.03699
Context: Lyman $\alpha$ blobs (LABs) are large-scale radio-quiet Lyman $\alpha$ (Ly$\alpha$) nebula at high-$z$ that occur predominantly in overdense proto-cluster regions. Especially the prototypical SSA22a-LAB1 at $z=3.1$ has become an observational reference for LABs across the electromagnetic spectrum.
Aims: We want to understand the powering mechanisms that drive the LAB to gain empirical insights into galaxy formation processes within a rare dense environment at high-$z$.
Methods: LAB 1 was observed for 17.5h with the VLT/MUSE integral-field spectrograph. We produced optimally extracted narrow band images in Ly$\alpha$ $\lambda1216$, HeII $\lambda1640$, and we tried to detect CIV $\lambda1549$ emission. By using a moment based analysis we mapped the kinematics of the blob.
Results: We detect Ly$\alpha$ emission to surface-brightness limits of $10^{-19}$erg s$^{-1}$cm$^{-2}$arcsec$^{-2}$. At this depth we reveal a bridge between LAB 1 and its northern neighbour LAB 8, as well as a shell-like filament towards the south of LAB 1. We find a coherent large scale east-west $\sim$1000 km s$^{-1}$ velocity gradient that is aligned perpendicular to the major axis of the blob. We detect HeII emission in three distinct regions, but we can only provide upper limits for CIV.
Conclusions: Various gas excitation mechanisms are at play in LAB 1: Ionising radiation and feedback effects dominate near the embedded galaxies, while Ly$\alpha$ scattering is contributing at larger distances. The HeII/Ly$\alpha$ ratios combined with the upper limits on CIV/Ly$\alpha$ ratios favour shock models over photo-ionisation. The alignment of the angular momentum vector parallel to the morphological principal axis appears odds with the predicted norm for high-mass halos, but likely reflects that LAB\,1 resides at a node of multiple intersecting filaments of the cosmic web.
(Abridged)
E. Herenz, M. Hayes and C. Scarlata
Tue, 14 Jan 20
16/72
Comments: 24 pages, 14 figures. Submitted to A&A, comments welcome